Mars,morning of Oct 18th.

[Quark]

Hi All,
Imaged Mars this this morning, my first attempt for this apparition.
At 4:59 CSST Mars was only 20 degrees above the horizon. My observatory is designed with a shutter at the bottom of the observing slot so that no extraneous light can enter my scope. Normally I don't open it, however to image Mars I had to open it completely to be able to just bring my scope to bear on the target.

The image was very difficult to focus as it was fairly unstable due to the low altitude of Mars. I have posted 1 of the 2 images captured. The radius of the disk of Mars this morning was 3.6 arc sec's.

The North Polar icecap is visible in this image. The CM for this image is long 193.9 degrees. The dark feature protruding up from the North East is the Mare Acidalium region and the smaller dark feature to it's West is the Nilokeras region. The dark feature extending from the North Polar region is Mare Erythraeum.

Thanks for looking
Regards
Trevor

[Rigel003]

Well done, Trevor. I was looking at it in the sky last night at about that time (after an all nighter photography session) and wondering when we'd be seeing some images from down under. 3.6 degrees radius?? You wish!

[Quark]

Thanks Graeme, yes it would be a stunning view if it was 3.6 degrees radius wouldn't it:rofl:. Have rectified the error in my post.

Cheers
Trevor

[Lester]

Hi Trevor, good on ya for getting an early Mars image showing detail as well. Are you sure on its diameter at 3.6", as my Sky 6 program lists its diameter at 7"?

[matt]

Nice image, Trevor.

Although I think you'll find you've understated the apparent diameter of Mars.

Astrocalc is showing it as 7.27" early this morning.

Cheers

[Quark]

Thanks Matt, we are both correct regarding the size of the disk of Mars. You have listed the diameter and I have listed the radius. The ephemeris generator that I use lists the radius of Mars in arc sec's for any UTC input.



Thanks Lester, yes it was an early morning and I had only just hit the sack from processing my Jupiter data from earlier in the evening.

The radius of Mars for this image was 3.624 arc sec's which would make the diameter just over 7.2 arc sec's. In my post I listed the radius.

[Liz]

Lovely to see an image of Mars - thankyou and well done Trevor :thumbsup:

[matt]

Oh.OK....

I'm not used to seeing the radius given as an object's size. I'm used to seeing its (entire) apparent diameter.

Thanks for clearing that up.

Can you explain the value/benefit of listing an object's radius rather than its apparent diameter?

[Quark]

Thanks Liz, I expect there will be many more images of Mars posted as it rises higher.



All of the ephemeris generators that I use for the various planets, list the apparent size of the disk of that planet as the radius. Thinking about this, the major significance would likely be in applying calculations for the gravitational affects that particular body exerts on other objects.

"The gravitational force between two bodies decreases inversely as the square of the distance between them."

To calculate the gravitational force, Eg; between an orbiting space craft and a planet it is the radius of the planet and altitude of the space craft that is used. I think this is why the radius is listed rather than the diameter in the tables that I generate.

[bird]

Nice work Trevor, we've had pea-soup fogs here in the morning lately, good to see you have some clear skies!

Bird

[Quark]

Thanks Anthony, the low altitude of Mars really is a problem combined with having to image it so close to dawn.

I think the only way I will be able to get good enough data for Tim at such a low altitude will be with my new IR filter.