This page last modified 2005 February 20
FAQ for uk.sci.astronomy
C. Astronomical Publications
D. Astronomical Software
Equipment – Choosing and Purchasing
Equipment – Maintenance
G. Astronomical Equipment –
H. Astronomical Equipment – Eyepieces
I. Astronomical Equipment – Accessories
Astronomical Equipment – Telescope Making
Astrophotography – Conventional Film
Astrophotography – Digital Cameras (DigiCams)
Astrophotography – CCD Cameras
N. Astrophotography –
Other Electronic Cameras
O. Visual Observation
P. Light Pollution
Q.Famous UK Astronomers
X. Other Useful Internet
Z. Requests for Other Sections
- Where is this FAQ located?
The primary location is
It is mirrored at
- What is uk.sci.astronomy?
"uk.sci.astronomy is a forum
for amateur and professional astronomers to discuss astronomy within the UK."
(from the newsgroup charter.)
- What is the charter of uk.sci.astronomy?
The charter is a
definitive description of what is and is not permitted on the newsgroup. It is
archived at http://www.usenet.org.uk/uk.sci.astronomy.html.
The full text of the charter is:
uk.sci.astronomy -- Astronomy in the UK
uk.sci.astronomy is a forum for amateur and professional
astronomers to discuss astronomy within the UK. Examples of
suitable topics for uk.sci.astronomy include:
Observing from the UK: Using the naked eye, binoculars,
telescopes, The Moon, Planets, Stars, The Sun, Comets, Meteor
Showers, Deep Sky Objects, Constellations, Aurorae, et. al.
Equipment: Choosing Telescopes/Binoculars. Choosing Accessories
(Finders, Drives, Eyepieces, Filters, Observatories) Building
Telescopes, Backyard Observatories, etc.
Astrophotography: Traditional, CCD, Other detectors, Image
Astronomy Software: Planetarium Programs, Deep Sky Programs,
Observatory Programs, Educational Programs
Relevant Social Events in the UK: Educational seminars, observing
Astronomical events visible from the UK: Lunar and Solar Eclipses,
Meteor activity, supernovae etc.
Tips & Techniques for Amateur Astronomers
Literature covering the topics listed above.
Is forbidden except for short (less than 10 lines) private adverts
for astronomy related items (telescopes, eyepieces, software,
books etc.) and announcements of events relevant to astronomy
in the UK. Blatant off-topic and commercial advertising is
All posts must be made in plain text; HTML and other types of
formatted text are forbidden. Posting URLs of relevant Internet
sites, where appropriate, is encouraged.
With the explicit exception of PGP signatures, all encoded
binaries are forbidden. Forbidden binaries include,
but are not limited to: pictures, sounds, word processor
documents, spreadsheets, executable programs and "business
cards". You are invited to read a guide on the World Wide Web
at http://www.usenet.org.uk/ukpost.html for further information
on how to configure your newsreader to post to uk.* newsgroups.
Anyone posting advertisements, binaries or other material contrary
to this charter may be reported to their ISP or postmaster.
- Can the charter be changed?
Yes, but it involves a non-trivial
process. For information on the procedure for changing charters, please see
- What conventions are there for posting to uk.sci.astronomy?
are the same as those for any uk.* hierarchy newsgroup, and can be found at
where you will also find advice on how to configure your newsreader
appropriately. In brief, these conventions/guidelines are:
- Post in plain text only (i.e.. no HTML, binaries, PDF, etc.)
- Set right margin to about 72 characters
- If layout matters (e.g. tabulation, ASCII-ART) compose (and read!) in
fixed-pitch font with no tabs
- Try to stay on-topic
- Trim quoted material – subscribers will have received the post which
you are following-up, so there is no need to quote it in full
- Do not top-post (i.e. do post your follow-up comments under the piece of
quoted material to which they reply). This enables readers to follow a train of
thought after multiple follow-ups.
- Use '>' to mark quoted lines.
- Use a signature-separator of "-- " (two dashes followed by a
blank space on a separate line). This enables newsreader software to exclude
signature lines from follow-ups.
- Restrict your signature to 4 lines
- Try to avoid cross-posting to multiple newsgroups.
- What is a troll?
A troll is someone who posts something
provocative to a newsgroup or other forum, not for the purposes of starting a
productive discussion but of creating a "stir". They usually
eventually go away if they are ignored.
- How do I deal with trolls and off-charter posting?
If you must
respond, please do so privately and not on the newsgroup..
If you wish to
complain, please do so to the "Complaints-To:" address in the header
of the offending post.
You can also report incidents of net abuse to the
using the appropriate posting format.
- What other astronomy newsgroups and electronic discussion media exist?
Skinner maintains an up-to-datelist of these at:
B. Astronomical Societies
- What national astronomical organisations are there in the UK?
- Where can I find out about local astronomical societies in the UK?
C. Astronomical Publications
- What UK astronomical periodicals are available?
- What other astronomical periodicals are available in the UK?
- What astronomy books are suitable for beginners?
There are very
many books suited to beginners. Those recommended on uk.sci.astronomy and
- Exploring the Night Sky with Binoculars
by Patrick Moore. A lot of useful information for people using modest
- Stars - A Collins Gem Guide by Ridpath and Tirion. Inexpensive
(shirt-)pocket-sized star atlas.
- The Observational Amateur Astronomer
by Patrick Moore (ed.) Good introduction to practical observing.
- Observers Handbook of Astronomy from Town & Suburbs
by Robin Scagell. Good general introduction to astronomy.
- Observing Variable Stars by David Levy
- Stars & Planets by Ridpath and Tirion. Informative at a
- Star Ware by Phil Harrington. A frequently updated guide to
available equipment, including accessories and eyepieces.
- The Oxford Dictionary of Astronomy by Ian Ridpath. A rich general
- The Complete Idiot's Guide to Astronomy by Christopher de Pree and
Alan Axelrod. Taks nothing for granted yet covers a lot of ground.
- Telescopes and Techniques by Chris Kitchin. A good intro to using
kit and understanding the "workings" of the celestial sphere.
- Turn Left at Orion by Consolmagno and Davies. An introduction to
observing the deep sky.
- Unveiling the Universe
by J.E. van Zyl. A good all-round theoretical astronomy book that deserves
to be much, much better known.
- What astronomy books are suitable for intermediate and advanced
There are very many books suited to intermediate and advanced
amateurs. Those recommended on uk.sci.astronomy and elsewhere include:
- Astrophotography for the Amateur by Michael Covington
- Astrophysical Concepts by Harwit
- Fundamental Astronomy by Karttunen et.al.
- Introductory Astronomy and Astrophysics by Zelik and Gregory
- Small Astronomical Observatories by Patrick Moore (ed)
- Stars and Their Spectra by James Kaler
- The Stars: Their Structure and Evolution by R.J. Tayler
- Telescope Optics: Evaluation and Design by Rutten and van Venrooij
D. Astronomical Software
- What planetarium programs are available for the PC?
numerous excellent planetarium programs available for PCs. Those recommended
are more comprehensive lists of astronomical software at:
- What planetarium programs are available for non-Windows platforms?
- What planetarium programs are available for hand-held computers?
the myriad of astronomically related software available for the Palm there are
three planetarium programs that stand out:
2Sky is commercial software. Planetarium and PleiadAtlas are offered as
nagware. Like most Palm software, a small registration fee is required for
continued, full-featured or nagfree use.
An evaluation download is available for each except The Sky
There is a comprehensive FAQ on astro software available for hand-held
- What software is available for observation planning?
planetarium programs include this facility. Dedicated observation-planning
- What software is available for telescope making?
for a list of suitable ATM software.
- What software is available for astronomical image processing?
processing software is used to manipulate the data held in a digital image. In
astronomy this is typically applied to digital camera images, ccd-images and
(less common) scanned photographs and slides. There are many different packages
available. In addition to general image-processing software like Adobe
PhotoShop® and Paint Shop Pro®, there is dedicated
astronomical image-processing software. Most CCD cameras come with some
image-processing software. Here is a reasonably extensive list of third-party
- What software is available for spectroscopy?
- Where can I obtain astronomical shareware?
E. Astronomical Equipment – Choosing and Purchasing
- What is the best telescope for a beginner?
The best telescope
is the one that will be used the most! A telescope that is easy to set up, easy
to use, and which has good mechanics and optics will be most likely to meet this
criterion. You should take portability into account if you will need to
transport it to an observing site. Cost is frequently a limitation for
beginners, and there is a cost below which it is advisable to save your money
until a better telescope is available. There is advice on telescopes available
in the UK, broken down into price ranges, at
Beginners are frequently advised to get binoculars instead of a
telescope. This is sound advice – most experienced observers continue to
use binoculars as well as their telescope or telescopes. Binoculars also have a
multitude of applications outside astronomy should the interest in observational
astronomy wane. There is advice on choosing binoculars for astronomy at
- How do I choose a first telescope?
Ideally, you should "try
before you buy". The best way to do this is usually to make contact with
your local astronomical society and attend an observing evening. Experienced
members will be pleased to advise you on your prospective purchase and you will
be able to arrange to try out equipment owned by the society or by members.
If you are unable to attend an astronomical society meeting and want
online advice, this is available at
There is advice on evaluating a telescope prior to purchase at
There is some excellent advice in this US-biased
FAQ. Phil Harrington's excellent book, StarWare, contains
information on a great deal of currently available astronomical equipment.
- What are the advantages of reflecting telescopes?
- The optics are free of chromatic aberration
- Usually give the most aperture per £
- What are the advantages of refracting telescopes?
- No obstruction in the light path to degrade the image
- Less affected by temperature changes than any other type
- The fully-enclosed tube reduces air-currents, leading to steadier images
- The optical components rarely require collimation - an especially important
consideration if the telescope is intended to be portable
- Easier to effectively baffle stray internal reflections that would
otherwise degrade the image
- Smaller optical tube for equivalent image quality
- What are the advantages of catadioptric telescopes?
- The fully-enclosed tube reduces air-currents, leading to steadier images
- In the case of Cassegrain configurations (SCT, MCT), the tube-length is
relatively short, rendering it easier to handle, transport and mount.
- How do I choose binoculars for astronomy?
There is advice on
choosing binoculars for astronomy at
- Where do I purchase new astronomical equipment in the UK?
are a number of reputable retailers in the UK. Most advertise in Astronomy
Now. If you wish to get opinions on a retailer, ask on the newsgroup.
- Where do I purchase used astronomical equipment in the UK?
are a number of options.
- Astronomy-UK is an excellent
and valuable resource that launched in 2005. It is provided free by a group of
UK amateur astronomers. It offers "classifieds" and an auction option.
- Astronomy Now has a "classifieds" page
- Astronomical society members may offer kit for sale at society meetings
- Local newspapers and "Free Ads" often carry adverts for used
- Astronomical kit is often auctioned on Ebay
- How safe is it to buy used astronomical equipment?
As with any
purchase, especially of used equipment, the best advice is caveat emptor.
That said, the majority of vendors of used kit are honest amateur astronomers
and reports on uk.sci.astronomy of someone being "fleeced" by a vendor
of used kit are exceptionally rare. Steps you can take to protect yourself
- Where possible, inspect and try out the kit before you purchase it
- Ask detailed questions about your intended purchase in order to ascertain
that it is what you want and is in the condition that you require
- Find out why the vendor is selling it. If he is upgrading, ask what he felt
were the shortcomings of the kit he is selling
- Before parting with any money, agree with the vendor exactly who pays for
what (e.g. P&P, return P&P) should the item not arrive in the advertised
- If the vendor is a "regular" on UK Astro-Ads, it is likely that
someone on uk.sci.astronomy will have bought from him – ask for opinions –
a reputable vendor will not object to being "checked"
- On Ebay, check the vendors record
- Can I buy directly from abroad?
Yes, but you need to be aware
of the following:
- Some manufacturers operate exclusive dealership regions, so you may not be
able to find a vendor
- Shipping and insurance will be more expensive than local shipping and
- You will need to pay import duty on the purchase price + shipping +
insurance if the item is purchased outside the EEC. The rate of import duty
depends upon the country of origin and the goods being imported. It varies
beteween 0% and 85%, with the vast majority being between 5% and 9% (astro kit
usually falls at the lower end of this bracket). For more information on import
duty see: http://www.sloanefox.freeserve.co.uk/importukduty.htm.
- You will need to pay VAT on the purchase price + shipping + insurance +
import duty if the item is purchased outside the EEC
- The carrier or his agent may (= "almost certainly will") charge
you a fee for clearing the item through customs and, where appropriate, paying
import duty and VAT on your behalf.
- Local agents may not be obliged to honour warranties on goods purchased
abroad, so these may need to be returned to the country of origin for warranty
- What do all the numbers mean?
- If only one number is given, this usually, but not always, refers to the
aperture of the instrument. E.g. an ETX 90 has an aperture of 90mm; a
G 9¼ SCT has an aperture of 9.25". Use common sense to
ascertain whether the aperture is given in inches or millimetres.
- If there are two numbers separated by the letter "f", with the
second number being smaller than the first , the first is the aperture, the
second is the focal ratio (i.e. the factor by which the focal length is greater
than the aperture. E.g. a 150 f 8 has an aperture of 150mm and a focal
ratio of 8; i.e. a focal length of 8 × 150 = 1200mm. This may also be
expressed in other ways, e.g. 150mm f/8 (which, incidentally, is more "correct").
- If there are two numbers, the first preceded by a "D" and the
second by an "F", the first is the aperture, the second is the focal
length. E.g. a D102/F1000 has an aperture of 102mm and a focal length of 1000mm.
- If there is one number, usually large, preceded or succeeded by a "×",
this number is the magnification. This is usually found on "department
store" telescopes which are best avoided. (But note that this caveat
applies only to astronomical telescopes, and does not apply to binoculars, or to
"spotter" telescopes intended for terrestrial use.)
- Where may I obtain manuals for second-hand telescopes?
F. Astronomical Equipment – Maintenance
- How do I clean telescope optics?
The short answer is: "As
infrequently as possible and very carefully." The optical surfaces of
mirrors and lenses are susceptible to damage if they are cleaned improperly, and
they have to be truly filthy before cleaning becomes necessary. If you must
clean the optics, first of all contact the manufacturer/supplier of the
telescope to ensure that any proposed action will not be deleterious to the
telescope or void the warranty, then:
- Small amounts of dust may be removed with a clean photographic puffer
brush. Work radially away from the centre. Only use the brush to remove
particles that cannot be blown off with the puffer
- Use collodion (sold as Opti-Clean®) to clean eyepiece lenses
and the lenses of small refractors, or corrector plates of small catadioptrics.
- To clean a mirror, carefully take it out of its cell and rinse it in
running water. If that doesn't remove sufficient muck, fill a basin with water
and a little bit of real soap powder/flakes (i.e. not detergent). Put the mirror
in and swill it around. With the mirror surface still under water, gently (i.e.
absolutely no pressure) swab the surface of the mirror from centre to edge with
lint-free cotton swabs, rolling the swab in the direction of travel, in order to
rotate any grime away from the optical surface. Do a little bit in the centre
first and examine the swabbed area with a magnifier or eyepiece to make sure
that you are not causing any damage. Rinse the mirror under copious amounts of
running tap water. Then rinse the mirror with distilled water, particularly if
you live in a hard water area. Water sold for topping up lead-acid batteries is
good for this purpose. Then leave it on its edge to drain and dry. At all times
take care not to touch the surface, and make sure it is safely supported and
protected whilst drying.
- To clean a refractor objective, remove all dust then make a solution of 6
parts distilled water, 1 part pure isopropyl alcohol, 2 drops mild washing-up
liquid. Dampen a lint-free pure cotton swab in the solution and gently (i.e.
weight of swab alone) swab from centre to edge, rolling the swab in the
direction of travel, in order to rotate any grime away from the optical surface.
Dry the lens by gently blotting it with a dry cotton swab or a piece of lens
- What is collimation?
Collimation is the correct aligning of all
the optical elements of a telescope.
- How do I collimate a Newtonian reflector?
The following web
sites have excellent advice:
- How do I collimate a refractor?
- How do I collimate a Schmidt-Cassegrain?
- How do I replace damaged optics?
manufacturer/supplier of the telescope and solicit help and advice from there.
- How do I repair/replace mechanical items?
manufacturer/supplier of the item and solicit help and advice from there. If you
are unable to get help from there, Barrie Watts of
Beacon Hill Telescopes
is sometimes able to make parts to order. Small parts can sometimes be made to
order by SRB – The Adaptor Factory
- How do I repair electrical/electronic components?
manufacturer/supplier of the device and solicit help and advice from there.
G. Astronomical Equipment – Mounts
- What is an altazimuth mount?
An altazimuth mount has two axes
of rotation. The altitude axis is horizontal, the azimuth axis is vertical.
- What is a Dobsonian mount?
A dobsonian mount is a simple
altazimuth mount that is usually made of wood, has bearings of Teflon®
running on Formica® (or similar substances), and is held together by
gravity. It is usually used for mounting Newtonian reflectors, and offers the
most cost-effective way to own a telescope of reasonable aperture. It is named
after the legendary John Dobson of the San Francisco Sidewalk Astronomers
/, who popularised it.
- What is an equatorial mount?
An equatorial mount has two axes
of rotation. The polar (or right ascension) axis is parallel to the Earth's axis
of rotation. The declination axis is orthogonal (at right angles) to the polar
- What is a fork mount?
The fork mount is an altazimuth or
equatorial mount in which the telescope tube is held between the "prongs"
of a two-pronged fork. The axis about which the telescope rotates is the
altitude or declination axis. The fork itself rotates about the azimuth or polar
axis. It is mostly used in its altazimuth form for refractors and in its
equatorial form for Cassegrain-type catadioptrics. The Dobsonian mount can be
considered to be a variation of an altazimuth fork. Fork mounts are usually the
most compact way of mounting a telescope, but the base of the fork can limit the
position of the observer's head.
- What is a German equatorial mount?
The German (so-called
because it was designed by the Bavarian astronomer, Josef von Fraunhofer)
equatorial mount carries the telescope tube at one end of the declination axis.
Its weight is balanced by counterweights on a shaft on the other end of the
declination axis. It is a very versatile mount, but the telescope has to be "flipped"
if it crosses the meridian.
- What are setting circles?
Setting circles are graduated scales
on the right ascension and declination axes of the telescope. They are an aid to
locating objects in the sky.
- What are digital setting circles?
Digital setting circles
employ optical encoders on the shafts of a mount. These encoders are read either
by a dedicated computer or, via an interface, by a desktop or laptop computer.
They serve the same purpose as ordinary analogue setting circles, but can be
configured to compensate for poor polar alignment (or for no polar alignment at
all) and usually come with catalogues of objects in the computer so that these
objects may be easily located.
- How do I add drives to my mount?
Contact the supplier or
manufacturer to see if there are dedicated drives available. If not, you may be
able to obtain them from JMI in the
- What is GOTO?
GOTO is a computerised system for driving a
telescope mount. A target object is selected, usually on a computerised handpad,
and the computer slews the telescope to the object.
- Can I computerise my telescope?
If the telescope mount can be
driven, it can be computerised. The ease with which this can be achieved depends
upon the mount.
- Dedicated computerised drive systems are available for some mounts. Contact
the manufacturer/supplier to ascertain whether this is the case for yours.
- Third-party drive computers are available for some mounts. See for example,
AWR and the
- There are DIY options available for those who have the necessary
inclination and ability. The most popular of these is
Mel Bartels' system.
- Can I use a planetarium program with my telescope?
upon the mount and the planetarium program, but the better planetarium programs
will work with the more common mount and drive systems. Contact the publisher of
the planetarium program to ascertain whether it can be used with your mount and
H. Astronomical Equipment – Eyepieces
- Why are there so many different eyepieces?
There are eyepieces
to suit almost every purpose and budget.
- What do the letters and numbers mean?
The number on an eyepiece
is its focal length in millimetres.
The most common letters and their
Er – Erfle. An extremely good relatively wide-angle
eyepiece with a flat field. Also used in good quality wide-angle binoculars. Use
at f/6 and greater.
H – Huyghenian. Most commonly provided with budget
telescopes. Use at f/10 and greater.
K – Kellner. A 3-element eyepiece
usually provided with budget telescopes. It is often used in binoculars. Use at
f/7 and greater.
MA – Modified Achromat. A variation on the Kellner.
– Orthoscopic. An excellent eyepiece, with a relatively small field of view
by today's standards. Use at f/6 and greater.
Pl – Plössl. A good
mid-range eyepiece. Currently probably the most common eyepiece. Use at f/5 and
- Which eyepiece is best for me?
The eyepiece is an essential
part of the optical system, so get the best that you can afford. In order,
acquire a medium, low and high power eyepiece:
- A low-power eyepiece is one that gives a magnification of approximately one
quarter of the telescope aperture in millimetres. Its focal length in
millimetres will be about 4 times the focal ratio of the telescope.
- A medium-power eyepiece is one that gives a magnification of approximately
equal to the telescope aperture in millimetres. Its focal length in millimetres
will be about equal to the focal ratio of the telescope.
- A high-power eyepiece is one that gives a magnification of approximately
one and three quarter times the telescope aperture in millimetres. Its focal
length in millimetres will be slightly more than half the focal ratio of the
- Are zoom eyepieces any good?
Modern astronomical zoom eyepieces
are of good optical quality and can replace two or more eyepieces from a set.
However, they tend to have narrow fields of view at the low magnification end.
- What is a Barlow lens?
A barlow is a negative lens that
increases the effective focal ratio of the telescope.
I. Astronomical Equipment – Accessories
- What are LPR filters?
For more information on applicability
of LPR filters, see Filter
Performance Comparisons for Some Common Nebulae.
- Broad-band Light Pollution Reduction filters are intended to block light
emitted by street lights (usually high- and low-pressure sodium and mercury
vapour). They also block starlight in the same frequencies. Therefore they offer
little or no significant improvement on objects that are comprised of stars
(galaxies, clusters, etc.) or those that reflect starlight (reflection nebulae),
but can improve emission nebulae.
- Narrow-band filters are very good on planetary and emission nebulae.
- Line filters (the common ones are O-III and H-beta) are excellent on most
emission nebulae, but reduce the visibility of of objects whose light is
starlight or reflected starlight.
For a graph of filter
transmission characteristics, see
- What colour filters are useful?
There is a list of colour
filters and their uses at
- What is a "minus violet" filter?
A minus violet
filter removes violet from the light, thus reducing the effects of chromatic
aberration in achromatic refractors.
- What is a star diagonal?
A star diagonal is a prism or mirror
that is placed between the focuser and the eyepiece of a refractor or
Cassegrain-type telescope, and which reflects the light through 90 degrees.
Without a star diagonal, observing near the zenith is extremely uncomfortable
unless the observer is reclining.
- What is a finder?
A finder is a small telescope with low
magnification (typically x8) and wide field (typically 7º) that is
piggy-backed on the main telescope tube, with which it is aligned. It usually
has a cross-web or other reticle in the eyepiece, thus facilitating the centring
of an object in the field of view, and thereby aligning the main telescope to
- What is a unit-power finder?
A unit-power finder is a
no-magnification reflex device that projects the image of a red dot or
concentric circles of known angular diameter onto the night sky and which can be
used as a substitute for, or in addition to, a normal finder. It is valuable as
a finder if the main telescope has a wide-ish field of view. The concentric
circles are an aid in star-hopping.
- Why do I need a red light?
Dim red light has the least effect
on night vision and is therefore preferred by astronomers.
J. Astronomical Equipment – Telescope Making
- Can I make my own telescope?
Yes. It is very common for
amateurs to make their own telescopes.
- Will it be cheaper than buying one?
This depends to what extent
you improvise and on how creative you are. You should not necessarily expect
that a first self-made telescope (usually 6" or 8" aperture reflector,
if you make your own optics) will be significantly cheaper than a commercially
made one; the benefits of a first telescope are usually the sheer pride and
satisfaction of having made one! However, the skills that you will learn can be
applied to more ambitious projects, where there are definite savings to be made.
- Where can I get more information?
There is a page that points
newcomers to telescope making to the required informational and material
resources at: http://www.astunit.com/tonkinsastro/atm/beginner.htm
K. Astrophotography – Conventional Film
- What is Astrophotography?
Astrophotography is the photographing
of astronomical objects. For anything other than photographing bright
solar-system objects, long exposures are required.
- What sort of camera do I need?
The minimum specification for
long-exposure astrophotography is:
Additional desirable specifications include:
- "B" shutter setting
- Manual shutter
- Cable shutter release
- Single lens reflex camera
- Tripod bush
- Interchangeable focus screen
- Where can I get a camera for astrophotography?
New cameras may
be acquired from some suppliers of astronomical equipment.
Some of the favourite cameras for astrophotography are no longer made and
are therefore only available used. Used cameras may be acquired from:
- Used camera shops
- Market stalls
- Car-boot sales
- Classified advertisements
- Internet auction sites
- UK Astro-Ads
- What common film is suitable for astrophotography?
specifications of film emulsions regularly change. A recent (November 2002)
article in Astronomy Now recommended the following:
- Kodak Elite Chrome 200 or E200 (slide)
- Kodak Elite Chrome 100 EC (slide)
- Fuji Provia 100 (slide)
- Fuji Provia 400 (slide)
- Kodak Supra 400 (print)
- Kodak Royal Gold 200 (print)
- Kodak Tech Pan 25 (print). This is a slow, fine-grained, B&W film that
must be hypered.
- How can I prevent star-trailing with a fixed camera?
with a fixed camera can be prevented by ending the exposure before the trailing
exceeds the resolution of the film. The formula for calculating this is T =
1000/(F × cos d), where T is the maximum exposure time in
F is the focal length of the lens in millimetres and d is the
declination of the centre of the star-field being photographed. For a 50mm lens
photographing stars on the celestial equator, this corresponds to a maximum
exposure of 20 seconds.
- How can I take long exposures without getting star-trailing?
can be achieved in several ways:
- What is piggy-back photography?
Piggyback photography is the
mounting of a camera onto a telescope or onto a mount that has a telescope
attached. The telescope may be used for guiding, but is not part of the
photographic optical system. The term is also loosely applied to a camera that
is mounted alone on an equatorial mount.
- What is prime-focus photography?
Strictly speaking it is
photography with the film plane directly at the focus of the primary mirror or
objective lens of the telescope. The telescope then replaces the camera lens.
The term is also used for photography with the camera at the focuser of a
Newtonian (strictly Newtonian focus) or Cassegrain (strictly Cassegrainian
focus) type telescope. The camera is directly attached to the telescope,
usually with a suitable adaptor.
- What is afocal photography?
In afocal photography, the camera
(with lens) replaces the eye at the eyepiece of a telescope. The camera is best
supported by a tripod. It potentially gives a high magnification and is suitable
for bright objects such as the Moon.
- What is eyepiece-projection photography?
photography, the telescope eyepiece projects the image onto the film plane. The
camera is directly attached to the telescope, usually with a suitable adaptor.
It gives a higher magnification than prime-focus photography.
- What other accessories do I need?
For prime-focus and
eyepiece-projection photography you need a camera adaptor that mates the camera
to the telescope tube or focuser, as appropriate. If you cannot get what you
require from your usual supplier, it is likely that
SRB will either have it or be able to
make it for you. For long exposure photography, some form of guiding is
- What is a guidescope?
A guidescope is a smaller-aperture
telescope attached to the main telescope or camera. It is fitted with an
eyepiece with a reticle. Its focal length should be at least that of the
photographic optical system.
- What is an off-axis guider?
An off-axis guider attaches between
the telescope tube and the camera. A small prism "picks off" a small
amount of the light and directs it to a reticle eyepiece. The eyepiece image is
generally less bright than that in a guidescope, but errors due to flexure
between the main scope and the guidescope and due to mirror-shift in the main
telescope are eliminated.
- What is a cold camera?
A phenomenon called reciprocity
failure that reduces the efficiency of the photographic emulsion is reduced
or eliminated at low temperatures. A cold camera uses dry ice (solid carbon
dioxide) to chill the film. They are technically very complicated to use.
- What is hypering?
Hypering is an abbreviation for hypersensitising.
It is a process by which the film is bathed in a gas containing hydrogen
(usually "forming gas", a mixture of hydrogen and nitrogen). This
nearly eliminates reciprocity failure.
- What is field rotation?
Picture a constellation or asterism
rising in the northeast, passing near the zenith, then setting in the northwest.
When it sets, it will appear "upside down" as compared to when it rose
– it has rotated. This rotation quickly becomes apparent in any
long-exposure astrophoto taken with a camera on a mount that is not properly
polar-aligned. Remedies include proper polar alignment or a computerised "field
derotator" that rotates the camera appropriately.
- Where can I get more information?
The acknowledged "bible"
for amateur astrophotography is Michael Covington's excellent Astrophotography
for the Amateur.
L. Astrophotography – Digital Cameras (DigiCams)
- How is a Digicam different from an ordinary camera?
digital camera ('DigiCam') uses a CCD chip in place of film as the image sensor.
It is 'digital' because all the image information is recorded as digital data
and stored electronically. The more expensive examples have larger CCD chips
offering better resolution. The size of the chip is quoted in Mega-Pixels
(millions of pixels), the largest commonly available is approx. 6MPixel.
- Is a Digicam better than a webcam for astro imaging?
webcam uses similar image sensor technology to the digital camera, though with
much lower resolution. The webcam does not possess any built-in recording
capability, nor sophisticated controls of exposure time or colour balance. The
lens is usually very simple, but a big advantage is that it can be removed for
Prime Focus work. Most digicam lenses cannot be removed.
- What features do Digicams offer?
To appeal to the general
public the vast majority of consumer digicams look very like compact 35mm film
cameras. Only a few high-end digicams replicate some of the functions of the
traditional SLR (e.g. interchangeable lenses). Most digicams have a retractable
optical zoom lens of short range with a built-in lens cover. All digicams offer
a 'digital zoom' which simply magnifies the central portion of the image.
Virtually all have a small TFT liquid crystal display which acts as a finder
and also shows the camera settings, and there is usually a small optical finder
too. Image data is stored on a removable memory card of varying capacity, and
there are several different formats in common use. All digicams are designed to
allow the transfer of image data to a personal computer from where the final
image can be printed.
- What are their limitations for Astronomical use?
were not designed with astronomical imaging in mind! However, amateur
astronomers can take advantage of certain special features they offer.
Exposures are limited to a maximum of few tens of seconds, and often less than
5 seconds, which means that faint objects cannot be recorded. With long (i.e.
greater than a few seconds) exposures the major limitation is digital 'noise'
in the image. Some of this noise (but not all) can be removed during image
processing. CCD cameras specifically designed for Astronomy are electronically
cooled to reduce this noise. Additionally, apart from a very few models,
digicams have non-removable lenses which means they cannot be used at the Prime
Focus of a telescope. Eyepiece-projection (Afocal Projection) is therefore the
only option for recording an image through an astronomical telescope.
- What features should I look for when purchasing a digital camera?
Ideally, the camera which generates the lowest noise in the image during long
exposures is the best option. The ease with which the digicam can be mounted
(attached to a telescope) is another feature to look for; adapters can be
obtained from SRB. Cameras with
retracting zoom lenses are difficult to attach solidly to an eyepiece and are
limited to some sort of bracket suspending it in close proximity to the
eyepiece. A great benefit is the option to remove the camera lens entirely, this
not only enables a firm connection to be made but also enables it to be used at
the telescope's prime focus (thus allowing wide-field imaging at lower
magnification). It also avoids vignetting which can be a problem with afocal
projection. Digicams possessing a threaded lens cell for accepting filters can
more easily be connected securely to a telescope.
- Why is the maximum exposure time important?
astronomical targets e.g. the moon, major planets, (and the sun using a suitable
filter) easily fall within the normal exposure range of a digicam. The
equivalent ISO rating (speed) of a digicam may be adjustable up to 800 or even
1600ASA if the camera offers control over its' electronic gain. For astronomy,
most deep-sky targets are so faint that they cannot be recorded within the
maximum exposure of a digicam. However, new and ever more sensitive models are
being produced, and as the technology advances then so more targets come within
range. Recent top-of-the-range models (e.g. Canon D60) extend the maximum
exposure time to a minute or more whilst still retaining low image noise, this
extends their target list to the brighter deep-sky objects (e.g. Nebulae such
as M42, bright globular clusters).
- Why is cooling important for best image quality?
of noise in the image is directly related to the temperature of the CCD sensor,
which is why astro CCD cameras are cooled. A digicam can be artificially cooled
(with a fan) which offers a moderate improvement. The electronics in a digicam
generate considerable heat when it's turned on, so a further improvement will
be seen if it is switched off and allowed to cool for a minute or so between
- Is the type of lens important for a digicam?
Because the only
option with most models is to use afocal projection through an eyepiece it is
worth investing in a digicam with a good-quality lens. Cheaper Digicams have
poor lenses which limit the achievable resolution.
- Should I use the Digital Zoom on my Digicam?
Digital zoom is
a feature of little use to ordinary photography because all it does is expand
the central portion of the image – which is easily be accomplished using a
computer anyway. However, it is of some use for astronomical imaging because it
makes focusing a little easier. Use the fully zoomed-in view to focus the
object, then zoom out again to properly frame the object.
- Is the type of memory chip my Digicam uses important?
type of storage medium or memory chip (e.g. Compact Flash, SmartMedia) is
unimportant, but it is very important that images be saved in 'uncompressed' or
'raw' format. This takes up more memory, and this is why most cameras have the
option to reduce file size by using JPG compression within the camera's
firmware. However, the effect of using compression is to introduce artefacts
which severely limit subsequent image processing. Because raw images are
preferred you need fairly large memory capacity in the camera.
- How do I get the images into my PC to process them?
most common PC interface protocol at time of writing is USB, older cameras used
serial (RS232) communications which is relatively slow. For serial interface
cameras it's usually possible to buy a device which enables the image data to
be read directly from the digicam's memory chip into the computer greatly
speeding up the process.
- Should I buy the digicam offering the highest resolution?
The latest multi-megapixel digicams with the largest chips compare well (but are
still inferior) to 35mm film in terms of raw pixel density (which equates to
image resolution). The difference however is of little concern for the prime
targets for which the digicam can be used. Even a digicam with a 1 Mpixel chip
– which is quite small these days - can produce very detailed images of,
for example, the moon and planets. There are two major types of CCD chip used
in digicams, standard silicon sensors and CMOS sensors. Once thought to be
inferior (lower sensitivity, higher noise), CMOS is the type of chip used in
the new Canon D60. Great advances in the implementation of CMOS technology and
on- camera image processing have resulted in less expensive and higher
- Will my Digicam produce 'True-Colour' images?
the great advantage of one-shot colour imaging which works well for
photographing brighter objects (Jupiter, Saturn etc.). It begins to fail with
longer exposures where colour balance changes with increasing length of
exposure. Post-processing can restore the colour balance to some extent though
much of the correction is guesswork. It is better to use tricolour imaging for
long exposures (that is, taking 3 separate monochrome exposures through red,
green and blue filters). For this method to be successful the colour sensitivity
of the chip has to be calibrated, a process which defines the exposure times
for each colour filter (the colour 'ratio'). Whilst most digicams do offer a
'black and white' mode in fact all that happens is that the chrominance data
(colour) is discarded from a colour image. Digicams have tricolour filters
incorporated into the CCD chips themselves, there is no way of taking a true
- What is the best way of supporting my Digicam for astro imaging?
There are three ways you can make use of it: You can use a fixed tripod to
record nice images of the constellations, and also events like Aurora displays
and sunsets. At night you can set the exposure to it's maximum length as star
trailing will probably not be a problem unless it's longer than about 30
seconds. Secondly, it is possible to 'Piggy-back' your digicam on a tracking
platform or driven equatorial telescope mount. However, most digicams do not
offer a sufficiently long exposure to make piggy-back mounting worthwhile. A
few do though – those digicams offering a minute exposure or longer would
benefit from being able to track the movement of the stars. Thirdly, most
amateur astronomers want to photograph what they can see through a telescope,
hopefully in greater detail and in colour. While an acceptable image can
sometimes be obtained holding the camera to the eyepiece, best results are
obtained with the camera firmly attached to the telescope. Two methods are in
common use: a special bracket attached to the Digicam's tripod socket holding
the camera close to the eyepiece, or (better) a threaded adapter connecting the
camera's lens directly to the eyepiece. For afocal projection it's best to use a
low-power, wide-field eyepiece (about 35mm), and then adjust the optical zoom
on the camera to avoid vignetting. Set the camera's focus to infinity and fine
adjust using the telescope's focuser. Although reasonable results can sometimes
be obtained using the digicam's autofocus in my experience this method is not
reliable for objects other than the moon or other high-contrast object.
- What is the best way to power my Digicam for astro imaging?
The digicam will come with a battery pack as standard but this will probably not
last long enough for an imaging session using a telescope. Quite often a long
time is spent fine tuning the focus, which rapidly drains the battery. Further,
cold conditions significantly reduce battery capacity. A better option is to
use an AC supply or a larger lead-acid battery.
- Can I control my Digicam from my computer?
If the digicam can
be firmly mounted to a telescope then remote control software (available for
newer Nikon, Olympus, Canon and some other cameras) allows virtually all
functions of the camera to be operated remotely using a computer. Older cameras
may be restricted to viewing the image and taking an exposure. If full remote
control is available the great advantage is that operating the often tiny
manual controls is avoided (very frustrating on a cold night!).
- What is the best way of focusing my Digicam for use with a telescope?
Accurate focusing is the most critical stage of astronomical imaging and it's
importance cannot be over-stressed. It is difficult to judge correct focus
using the small built-in display so either use an external monitor (a small TV
or PC display helps) or another focusing aid such as a Hartmann or hole-mask.
Use maximum digital zoom whilst focusing so that errors are more easily seen,
then back off the zoom to frame the object normally.
- How do I avoid vibrations spoiling the exposure?
digicam's delayed shutter feature to allow vibrations to stop before the image
is taken. Take several exposures of each object (at least 3, and more if the
'seeing' is less than excellent).
- I took some images, how can I improve the result?
images will benefit from some degree of post-processing using a computer program
designed for the job. This involves reducing spontaneous noise by subtracting
'dark' (or blank) frames, and averaging multiple frames. Most image processing
programs, and all of the astronomy oriented ones, allow multiple images of the
same object to be 'stacked' or averaged. After sorting out and discarding
obviously poor quality examples the remaining images can be compiled in this way
to provide an image possessing lower background noise with more detail. After
that, further enhancement can be achieved by use of sharpening filters and also
correcting the colour balance. The best tool for the job is a specific astro
image processing package (e.g. MaximDL or AstroArt), but if you have a good
working knowledge of Paintshop Pro or Adobe Photoshop most jobs can be done
using these. Astro image processing programs also offer special procedures
called deconvolution to recover blurred detail from images slightly out of focus
or trailed. These programs are also specifically designed to best deal with low
contrast and poor signal-to-noise ratios typical of astronomical images.
- Should I buy an expensive Digicam now or wait a while?
Digicams are currently on the threshold of being a viable tool for the budding
astro-imager. It is unlikely however, that for long exposure work it will be
able to replace the functionality of a dedicated astro CCD camera any time soon.
Nevertheless, amazing results have been achieved by amateur astronomers using
both digital cameras and also webcams, extending their range to capturing
stunning images of the brighter deep-sky objects. These results have been
achieved through both improved CCD technology in the cameras, DIY techniques for
cooling the chip and electronics, and development of image processing techniques
to improve the final image. Progress is a continuous process so digicams
definitely have a promising future.
- Where can I find more information on using a Digicam for astro imaging?
[URLs of Various websites devoted to using digital cameras in astronomy]
Digital camera astro imaging group (Yahoo).
M. Astrophotography – CCD Cameras
This section is currently being written. Until it is available, visit:
N. Astrophotography – Other Electronic Cameras
Until this section is written (offers gratefully received!), you are invited
to visit the QuickCam and
Unconventional Imaging Astronomy Group. If you require an adapter to mate
the camera to teh telescope, try SRB.
O. Visual Observation
- Where can I find out what is happening in the sky?
- How do I record observations?
Notes and drawings can be made
with soft pencil and paper; mini-tape recorders can be used for verbal notes. In
both cases, they can be written up in neat afterwards. Essential information
- Date and Time
- Sky and weather conditions
- Instrument(s) used
- Object(s) observed
- Impressions of object
- How can I see fainter objects?
The following have all been
known to work:
- Averted vision. This is looking to one side of the object so that its light
falls on the more sensitive periphery of the retina.
- Improved observational skills
- Larger aperture
- Trying different magnifications
- Jiggling the telescope
- Hyperventilating (oxygenating the retina)
- Choose a darker night and/or observing site?
- Why can't I see Saturn's rings?
Reasons have included:
- The observed object was not Saturn
- Insufficient magnification (use at least ×30)
- Planet so close to the horizon that rings merely appear as extremely oblate
- You are in the plane of the rings! Wait a few years. (This is not a problem
again until late 2008.)
- How do I know if what I am seeing are Jupiter's moons?
- Compare positions with those in a planetarium program or published in an
astronomical magazine or observing handbook.
- The Jovian moons fall into a nearly straight line that is parallel to the
bands on the planet's surface
- The Jovian Moons move relative to each other and to background stars.
Background stars do not move relative to each other.
- How can I estimate the magnitude of an object?
Compare it to a
'standard star' of known magnitude. The magnitude scale is calibrated by
arbitrarily assigning a magnitude to a star – the magnitudes of other stars
follow by comparison to this standard star. In practice, there are many standard
stars, so distributed that standards of different spectral types are likely to
be reasonably close to any star being observed. One should choose a star of
similar spectral type when estimating a magnitude of another star – the eye
and photometers are differently sensitive to different wavelengths. (See also
- What is limiting magnitude?
This can have different meanings
according to the context.
- When referred to a star atlas, it is the approximate magnitude of the
faintest stars included.
- When referred to the sky, it is the dimmest stars that would be visible at
the zenith. It is sometimes referred to as naked eye limiting magnitude or NELM.
It is usually estimated by counting the visible stars in a clearly defined
region of sky, such as the Square of Pegasus, then referring to a standard
- When referred to an instrument, it is the faintest stars visible with the
instrument under ideal conditions. The theoretical limiting magnitude, Mlim,
of a telescope with an aperture, D, can be calculated by the formula: Mlim
= 6.5 - 5 log d + 5 log D (where d is the pupil diameter of the human eye).
However, the predictions of theory do not always accord with observation and the
observed magnitude limits for different apertures are closer to these values for
These are data for experienced observers in ideal
conditions. Haze, inexperience, and poor equipment can all reduce the value of
the limiting magnitude.
P. Light Pollution
- What is light pollution?
Light pollution is artificial light
that shines where it is not required or where it is detrimental in any way to
the environment. For astronomers the main problems are skyglow (brightening of
the sky by light reflecting off water droplets and particulate matter) and light
- What is light trespass?
Light trespass is artificial light that
shines on your property from sources that you do not control outside your
property. This may be from streetlights, a neighbour's poorly directed security
light, light from a local recreational facility, or any other source.
- How can I get light pollution and light trespass reduced?
can get up-to-date information about what you can do from
The Campaign for Dark Skies
- How can I observe in light-polluted areas?
Aids to observing in
light-polluted areas include:
- LPR filters
- Use a CCD camera (the unwanted light can be removed by software)
- Use larger apertures (effective on point objects)
- Which areas of Britain have the least light- pollution?
guide to how your county compares to other areas, visit
Q.Famous UK Astronomers
- Who are the UK astronomers of note?
Those marked with an
asterisk (*) have held the post of Astronomer Royal
Adams, John Couch -
Born 5th June 1819, died 21st January 1892
Airy, George Biddell* - Born
27th July 1801, died 2nd January 1892
Bell-Burnell, Jocelyn - Born 1943
Bliss, Nathaniel* - Born 28th November 1700, died 2nd September 1764
James* - Born 1693, died 1762
Burbidge, Eleanor Margaret Peachey - Born 12th August 1919
Geoffrey Ronald - Born 24th September 1925
Christie, William H.M.* - Born 1845, died 1922
Dawes, William Rutter - Born 1799, died 1868
Dyson, Frank W.* - Born 8th January 1868, died 25th May 1939
Arthur Stanley - Born 28th December 1882, died 22nd November 1944
Fearon - Born 4th July 1789, died 25th July 1831
Flamsteed, John* - Born
19th August 1646, died 31st December 1719
Graham- Smith, Francis* - Born
Halley, Edmond* - Born 1656, died 1742
Hawking, Stephen William -
Born 8th January 1942
Henderson, Thomas - Born 28th December 1798, died
23rd November 1844
Herschel, Caroline - Born 16th March 1750, died 9th
Herschel, John - Born 7th March 1792, died 11th May 1871
Herschel, (Frederick) William - Born 1738, died 1822 Hewish, Antony - Born
11th May 1924
Hoyle, Fred - Born 24th June 1915, died 20th August 2001
William - Born 7th February 1824, died 12th May 1910
Jeans, James Hopwood
- Born 11th September 1877, died 16th September 1946
Spencer* - Born 29th March 1890, died 3rd November 1960
Lassell, William - Born 18th June 1799, died 1880
Norman - Born 17th May 1836, died 16th August 1920
Lovell, Bernard - Born
Maskelyne, Nevil* - Born 5th October 1732, died 9th February 1811
Moore, Patrick - Born 4th March 1923
Newton, Isaac - Born 1642, died 1727
Payne-Gaposchkin, Cecilia - Born 1900, died 1979
Penrose, Roger - Born 8th August 1931
Pogson, Norman Robert - Born 1829, died 1891
Pond, John* - Born 1767, died 1836
Rees, Martin John* - Born 23rd June 1942 Ryle, Martin* - Born 1918, died
Thom, Alexander - Born 1894, died 1985
Wolfendale, Arnold Whittaker* - Born 1927
Woolley, Richard* - 24th April 1906, died 24th December 1986
- Who are the Astronomers Royal?
Flamsteed, John 1675-1719
Halley, Edmond 1720-1742
Bradley, James 1742-1762
Bliss, Nathaniel 1762-1764
Maskelyne, Nevil 1765-1811
Pond, John 1811-1835
Airy, George Biddell 1835-1881
Christie, William H.M. 1881-1910
Dyson, Frank W. 1910-1933
Jones, Harold Spencer 1933-1955
Woolley, Richard 1956-1971
Ryle, Martin 1972-1982
Graham-Smith, Francis 1982-1990
Wolfendale, Arnold Whittaker 1991-1995
Rees, Martin John 1995-
- Why is the image inverted/reversed?
This is a function of the
optics. Assuming there are no "image erector" lenses or similar in the
optical system of an astronomical telescope, the orientation of the image will
depend upon the number of reflections in the system. It is irrelevant to
astronomy – a star has no "right way up".
- What is magnitude?
The magnitude is the brightness of an
astronomical object. As observers, we are primarily in the apparent
magnitude, which is the magnitude we perceive. There is also absolute
magnitude, which is the magnitude that a star would appear at a distance of
10 parsecs (except for asteroids it is at 1 AU with zero phase angle).
The magnitude scale that we use was derived from Hipparchus, who
informally classified stars into different magnitudes. The first to appear at
dusk were "1st magnitude" and the last to appear were "6th
magnitude". The scale was formalised by Pogson, who formalised it into a
logarithmic scale in which a 1st magnitude object is 100 times as bright as a
6th magnitude object.
The magnitudes assigned to standard stars are such that they are
consistent with each other, and the calibration is based on a star of magnitude
1.0 having an energy of 9.87 × 10-9 W m-2 at the
top of Earth's atmosphere.
There are other types of magnitude relating to specific parts of the
electromagnetic spectrum.Here are the visual magnitudes of some common
[Source: Tonkin, AstroFAQs]
||Venus (at its brightest)|
||Jupiter (at its brightest)|
||Mars (at its brightest)|
||Sirius (brightest naked eye star)|
||The approximate magnitude of Alpha Centauri, Arcturus, Vega, Rigel|
||Saturn (at opposition)|
||The approximate magnitude of Antares, Spica, Pollux|
||The approximate magnitude of Polaris and the stars in Orion's Belt and the
||Approximately the faintest stars visible in brightly-lit urban skies|
||Approximately the faintest stars visible in dark, transparent skies|
- What is gravity?
In general terms, gravity is a force of mutual
attraction amongst all objects. Its importance in astronomy includes the
See John Stockton's
Gravity FAQ for more
- Satellite orbits
- Planetary systems
- Binary and multiple star systems
- Black holes
- The history of the universe
- What is relativity?
This is best answered by
- Why do astronomers believe that the Universe is expanding?
galaxies have redshifted spectra, indicating that they are receding. The greater
the distance the greater the redshift and apparent rate of recession. This is
consistent with an expanding universe.
- What is the Big Bang Theory?
If the Universe is expanding,
common sense suggests that it was smaller in the past. Taken to its extreme,
this suggests that the universe was once a point; prior to that it did not
exist. The theory in which the universe was suddenly created from a "singularity"
is the Big Bang Theory, which is currently the dominant theory of cosmology. The
name was coined in derision by the late Sir Fred Hoyle, who supported a
different theory of the universe.
- What happened before the Big Bang?
If the theory is correct,
time came into existence with the Big Bang, so the conditions that gave rise to
the Big Bang are probably unknowable.
- Will Earth be hit by a "doomsday asteroid"?
is not a matter of "if", but of "when". It may be millions
of years in the future, but we currently have no way of knowing as we only know
the orbits of a small fraction of the NEOs (Near Earth Objects).
- Can I do anything about "doomsday asteroids"?
Tate, Director of Spaceguard UK, writes:
are available at:
There are a number of very efficient NEO detection programmes in the USA
that are out performing amateur searchers by a significant margin, though with
larger telescopes (12" to 16" bracket) and high end CCDs discovery is
still possible. The most valuable contribution that the amateur can make is
performing follow-up observations of NEOs discovered by the professional
programmes. There is an excellent guide to Minor Planet Astrometry available at
valuable contribution that amateurs can give is to pursue those who control the
purse strings, in other words, write to your locally elected officials. The
government began to take the NEO hazard seriously in 2000, but, since then,
there has been an almost total lack of activity.
- Why does the Moon appear larger on the horizon?
This is the "Moon
Illusion". It is an optical illusion, related to the Ponzo illusion,
resulting from a combination of the phenomenon of size constancy and our
perception that the celestial sphere is flattened (i.e. that the zenith is
nearer than the horizon). See the
- How can I combat dew formation on my telescope?
Dew forms when
the temperature of a surface falls below "dew point". Telescopes cool
by radiative cooling, so dew can be counteracted by reducing radiative cooling
of optical surfaces and by reducing the amount of warm moist air (e.g. breath)
that comes into contact with them.
- Dew caps provide the simplest way of shielding object glasses and corrector
plates from the sky, but very few telescopes are provided with sufficiently long
- The existing dew-shield or the air in the vicinity of the optic can be
actively warmed by a proprietary product such as the Kendrick Dew Zapper®,
or by DIY options such as resistance wire or strings of resistors.
- There are two obvious ways of warming eyepieces: a clean inside pocket or
some form of electrical heating. Folding down eye-cups can reduce the rate at
which dew accumulates.
- If dew forms, it can be removed by warm dry air from, e.g. a "traveller's"
- How can I keep warm when observing on cold nights?
- Wear layers of warm clothing, with a wind-proof outer layer. Clothing worn
next to the skin should "wick" water (sweat) away from the skin.
Examples of this include motorcycle and ski garments. There is an excellent
article on layering
- Body-temperature can be regulated with a warm hat, which is easier to
adjust than it is to remove or add layers of clothing.
- Felt-lined snow-boots keep feet toasty-warm.
- Hunter's or fisherman's gloves with "split thumbs" and/or
fold-back finger tips keep the hands warm whilst permitting delicate adjustments
to be made.
- Mild exercise prior to observing can increase metabolism (and thus raise
body temperature) for several hours.
- Drink hot, sweet, non-diuretic drinks, especially just prior to an
observing session. In addition to the warmth from the drink, the body's
extremities cool more rapidly if it becomes even slightly dehydrated.
- Where can I get current weather information?
- How are eclipses caused?
An object is eclipsed when it passes
into the shadow of another. Therefore an eclipse of the Moon occurs when the
Moon passes into Earth's shadow, i.e. when the Moon and Sun are on diametrically
opposite sides of Earth. An eclipse of the Sun is, strictly speaking, an occultation
of the Sun, i.e. the Sun's disc is occulted (hidden) by the Moon for an observer
- What are the causes and effects of tides?
Sea-tides are caused
largely by the gradient, at the Earth, of the Moon's gravitational field; the
Sun is the only other body which makes a significant contribution. Tides tend to
cause the orbits of planets and moons to circularise and synchronise. For more
- How is time related to astronomy?
- How is the calendar related to astronomy?
- What units are used in astronomy?
Astronomy is an international
undertaking and therefore uses Systeme International (SI) units. In addition,
the following units are also used:
- The Ångstrom unit (1 Å = 0.1 nm) is still often used in
- The Astronomical Unit (1 AU = 149 597 870 660 m), the mean
separation of the Earth and Sun, is used to measure distances within the solar
system or other star/planet systems.
- The light year (1 l.y. = 9.4605 × 1012km), the
distance travelled in vacuo by light in one tropical year, is used to measure
distances outside the solar system.
- The parsec (1pc = 3.0857 × 1013 km) (3.2616 l.y.),
the distance at which a star has an annual parallax of one arcsecond, is used to
measure distances outside the solar system. It is the distance at which 1 AU
subtends an angle of 1 arcsecond.
- What co-ordinate systems are used in astronomy?
commonly used are horizontal co-ordinates (altitude and azimuth –
referenced to the plane of the horizon and due north) and equatorial
co-ordinates (right ascension and declination – referenced to the plane
of the equator and the vernal equinox). For more information on these and the
conversion between them, see:
Also encountered are ecliptic co-ordinates (ecliptic latitude and
ecliptic longitude – referenced to the plane of the ecliptic and the vernal
equinox) and galactic co-ordinates (galactic latitude and galactic
longitude – referenced to the galactic plane and the galactic centre).
- Where can I find satellite predictions?
The most popular (to
the extent that it is sometimes inaccessible owing to business) seems to be:
Heavens-Above; have your
latitude and longitude to hand. Other useful sites include:
- Where can I get information about solar system objects?
- What do all the strange new words mean?
There is a hyperlinked
Glossary of Astronomical Terms at
X. Other Useful Internet Resources
These are useful links that don't quite fit anyhere else. They are in
- Who maintains this FAQ?
This FAQ is maintained, on behalf of
the subscribers to uk.sci.astronomy, by
Stephen Tonkin, to whom corrections, updates and suggestions should be emailed (i.e.
don't assume that he will automatically see them on uk.sci.astronomy).
The text version of the FAQ is maintained by David Clapham. Copyright
remains as assigned in the HTML original, which should be regarded as
definitive if any errors, omissions or contradictions between the two documents
- Who contributed to this FAQ?
David Clapham (text version;
proof-reading and HTML checking of original; numerous suggestions and additions)
Pete Lawrence (D3, D6)
Graeme Skinner (A8, Q)
Stockton (W15, W20, W21, numerous links, proof-reading and HTML checking)
- Where did this FAQ originate?
The original FAQ for
uk.sci.astronomy was initiated and written by Dave G Smith. We, the current
authors of the FAQ, acknowledge, with thanks, Dave's initiative.
Z. Requests for Other Sections
There have been requests for sections or subsections, or expansions on the
- Solar System
- Other FAQs
- UK Astronomical Web Sites
If you are able to assist by writing one or more of these, please email the
maintainer of this FAQ with your offer.
This document, as a collection, is © 2002, 2003,
Stephen Tonkin; contributors retain copyright of their contributions.
Permission to use, copy and distribute this unmodified document by any means
and for any purpose except profit purposes is hereby granted, provided that both
the Copyright notice and this permission notice appear in all copies and
part-copies. Reproducing this FAQ by any means, included, but not limited to,
printing, copying existing prints, publishing by electronic or other means,
implies full agreement to the above non-profit-use clause, unless the maintainer
and/or contributor has given prior written permission. This FAQ is provided in
good faith "as is". Any express or implied warranties, including, but
not limited to, any implied warranties of merchantability, accuracy, or fitness
for any particular purpose, are disclaimed. If you use the information in this
document in any way, you do so entirely at your own risk.
Should the maintainer not post to uk.sci.astronomy for a period exceeding 90
days, the copyright of this document, as a collection, may be assigned to a new
maintainer who shall be selected by the other contributors to this FAQ. This
condition of copyright assignment shall also pass to the new maintainer.