as seen through a range of telescope
apertures in the weeks surrounding
closest approach
(Oct-Nov 2005)


A super-sharp image of Mars courtesy of Hubble Space Telescope
Aperture 2.4m (94" 2400 mm)

Below are simulations of how Mars would appear through telescopes
with apertures from 2.4" to 12" under (1) perfect seeing condition and
(2) moderate turbulence (more typical of observing conditions).

If you have persistent problems seeing any detail at all see troubleshooter.

Images prepared by Aberrator V2.53 
refering to Mars at apparent size of about 25 arc seconds

Aperture of Telescope (1) View in Perfect Seeing (2) View in Moderate Seeing
2.4" (60 mm)
3.5" (90 mm)
4" (105 mm)
5" (120 mm)
6" (150 mm)
8" (200 mm)
10" (254 mm)
12" (300 mm)

1. Is the begin with, keep on
g with the above points in mind and you are sure to get a good
night when Mars will deliver! As a rule, with goodptics, under good 
1. Are the optics of your scope good quality. Bad optics will never focus sharply and image contrast will always be poor. In a reflecting telescope if the mirror is homemade, has it been tested so that you know if it can perform well?

2. Collimation, (optical alignment) could be the problem. Visit this site on how to fix this and many other telescope problems.

3. Bad seeing (turbulence). If Mars is low in the sky, atmospheric turbulence can obliterate contrast and detail on the planet. Wait for it to gain altitude say greater than 30 degrees. Sometimes seeing may be bad even when Mars is high. It depends on atmospheric conditions at the time.

4. Speaking of turbulence. Thermal currents inside the telescope tube will have a similar effect if the scope is transported from a warm interior to cold outdoors. Allow the scope 1/2hr to 1hr to reach thermal equilibrium outdoors before beginning to search for planetary detail.

5. Even in an 8" with good optics and good seeing conditions the dusky markings on the planet require some patience and practice to discern especially if you are new to observing. The bright polar cap however should be easily visible.

6. I have been observing Mars regularly with a 3.5" Maksutov. The polar cap is always visible and the most prominent markings (Sinus Sabius, Syrtis  Major, Mare Sirenum, Mare Cimmerium and the dark hood around the ever  shrinking polar cap) are identifiable most of the time. They are better with my homemade 6" newtonian.

7. Sometimes a larger aperture performs worse than a smaller aperture under bad seeing conditions. You may have been caught out by this. It depends on the prevailing general seeing conditions in your locality which may be determined by season, adjacent buildings, bodies of water, vegetation and other such factors. You might like to try a 4" or 6" aperture mask over the top end of the scope to see if this beats the seeing conditions. It might also cure a badly figured homemade mirror if that is the problem.

8. A red or orange filter will help if the seeing is good to begin with. Otherwise it makes little difference. On a recent occasion an orange filter improved the contrast on Mars in the 3.5" Maksutov but made no difference in the 6". A filter however, even if it does nothing else, can reduce the "glariness" of the planet so that it is easier on the eye. 

9. Provided the optics in your scope are good to begin with, keep on persisting with the above points in mind and you are sure to get a good night when Mars will deliver! As a rule, with good optics, under good seeing conditions, a larger aperture will always outperform a smaller one.

Compiled by Martin Lewicki : mlewicki *at* ozemail dot com dot au

Also available : Martin's other astronomy articles