Mars Parallax Night - October 22/23 2005
Purpose
To measure the distance from the Earth to Mars using parallax.
Please check back regularly as project plans may be subject to change!
UPDATE #1
2005-10-21 08:00 UT
The main imaging times will remain as 01:00:00 and 02:00:00 UT but the project will
be extended to cover 00:00:00, 03:00:00 and 04:00:00 UT as well. Imagers are urged to
try for the other times to provide additional backup results and extend the imaging group
further west.
If there are imagers further to the east that would like to join in, please contact me at
pete dot lawrence at gmail dot com and let me know.
UPDATE #2
2005-10-22 09:00 UT
A field test shot is now available (bottom of this page) as an example of the type of image required. Note that when this shot was taken
there were no close stars so the field of view is larger than ideally required. When I come to do the
final image on the morning of the 23rd, I'll 2x Barlow this shot to improve the scale. Note that the result doesn't need
to be beautiful - it's the positional information that's required. The set up I used
managed to capture stars as faint as +13.6 with a 6s exposure (useful as it was blowing a gale).
Don't worry about using longer exposures, this just happens to be appropriate for my set-up.
I should also add that it's important that the time of the exposure is as accurate as possible.
Method
Two CCD/DSLR field shots of Mars taken at a co-ordinated
time (01h00m00s and 02h00m00s UT) are required...
If these times cause problems because you cannot see Mars
or it's altitude will be too low and you would
like to take part in the project,
please let me know at the email address given below. Other imaging times
can be arranged if necessary.
Shot 1: Centered on the specified time, this shot should show Mars and at least two field stars.
Shot 2: Taken immediately after shot 1, this should be exposed to show the limb of Mars. Field stars are not
required in shot 2.
Shot 1 is likely to be several seconds long. As a consequence, Mars will be over-exposed. This is not a problem
as long as shot 2 is taken immediately after 1. Additional accuracy can be had by taking a limb shot (shot 2) before and
after shot 1.
Shot 1 should be time centered on the co-ordinated imaging times (01h00m00s and 02h00m00s UT).
For example, if you need an exposure of 20s (this will vary for different instrument setups) to pick up field stars,
shot 1 should be started 10s before the co-ordinated imaging time. Here's an example:
Agreed co-ordinated imaging time = 01h00m00s UT
Shot sequence (assuming a 20s exposure is required for field stars and 0.1s for the limb shot) will be
[00h59m50s] Shot 1, ends at [01h00m10s], [01h00m30s] Shot 2.
In this example, 20s has been assumed to be the time to change the exposure settings in order to set up for shot 2. Of course
this is down to the individual observer and equipment. Faster is better.
An advanced sequence would be...
[00h59m30s] 0.1s exposure for the limb (extra shot 2)
[00h59m50s] 20s exposure for field stars (shot 1)
[01h00m30s] 0.1s exposure for the limb (shot 2)
Practicalities
Mars needs to be as large as possible in the field while maitaining at least two
reference stars. The charts below show three different field-of-views. The 18' or 9' fovs are desirable. The larger the
field the more accurate the calculation.
The co-ordinated global imaging times are 01h00m00s UT and 02h00m00s UT. If the 01h00m00s
slot fails, then this strategy provides a second chance an hour later.
If you get an image and would like to participate in calculating the distance to Mars on the night of
October 22/23 2005, please let me know at
pete dot lawrence at gmail dot com
Best of luck and clear skies!
