Mars - Bright Western Limb

[procky1845]

Hi,

Was out observing Mars on Friday night (7th Aug) and noticed that the West limb was particularly bright, I was wondering if anybody knew the reason for this i.e. is it just the reflection of sunlight or is there some other reason? I haven't noticed this before but the last time I observed Mars was a few months ago in the morning twilight.

I've attached my sketch from the evening (admittedly not the best, sorry) which does show the brightness at the limb.

Thanks,

Lee

[dweller25]

I have seen that too - I think it’s morning mist/dew/fog/frost.

Very good observation and drawing 👍

Edited August 10, 2020 by dweller25

[procky1845]

51 minutes ago, dweller25 said:

I have seen that too - I think it’s morning mist/dew/fog/frost.

Very good observation and drawing 👍

Oh wow, that's quite cool.

I was confused by your statement at first but the terminator we see would be the night time terminator wouldn't it so that does make a lot of sense!

Thanks!

[mikeDnight]

That's a great sketch Lee and you've caught some interesting detail, depicted very subtly within the darker albedo features. I can see in your sketch that you've recorded a perfect outline of Solis Lacus ( the Eye of Mars) right on the central meridian. Along the bright limb you have undoubtedly included the bright cloud around Olympus Mons, shown as a brighter indent at around 2 o'clock, and there are bright regions coming onto the disk that when combined with the morning haze and thin cloud in Mars' atmosphere creates the bright limb. You have a very keen observing eye. Thanks for posting your sketch!

Attached is a 2016 cylidrical grid map of Mars showing the latitude and longitude of Martian features with the same reversed orientation as in your telescope which you may find helpful. You can see some bright regions i mentioned to the right of Solis Lacus, and Olympus Mons at 130° visible close to the limb in your sketch.

[procky1845]

8 minutes ago, mikeDnight said:

That's a great sketch Lee and you've caught some interesting detail, depicted very subtly within the darker albedo features. I can see in your sketch that you've recorded a perfect outline of Solis Lacus ( the Eye of Mars) right on the central meridian. Along the bright limb you have undoubtedly included the bright cloud around Olympus Mons, shown as a brighter indent at around 2 o'clock, and there are bright regions coming onto the disk that when combined with the morning haze and thin cloud in Mars' atmosphere creates the bright limb. You have a very keen observing eye. Thanks for posting your sketch!

Attached is a 2016 cylidrical grid map of Mars showing the latitude and longitude of Martian features with the same reversed orientation as in your telescope which you may find helpful. You can see some bright regions i mentioned to the right of Solis Lacus, and Olympus Mons at 130° visible close to the limb in your sketch.

Thanks for your help, thats really interesting, I hadn't identified those features. (Also thank you for the map, it is difficult constantly having to do the mental flip with the standard maps).

I find it really tricky to identify the features as different maps seem to depict them in different orientations and configurations. For example Mare Erythraeum on the map I was looking at when I tried to label the sketch (first pic below) seems to depict it as a large darker area, where as on the map from the BAA website (second pic below) it seems to be depicted as a smaller horizontal dark region. 

 

 

[mikeDnight]

I agree it is often quite difficult to interpret maps of Mars and relate the markings to the real life view through the telescope. For that reason I decided to make maps of my own based on observations I made at the eyepiece, rather than having to struggle along trying to flip images in my mind. Also, the view at the eyepiece is often far different from that of the maps.  My first map was drawn in 2003 using a 5" refractor.but I didn't use a diagonal so it's south at the top. Mars back then was 25 arc seconds and high in the sky, and I made all my observations using a 7mm Nagler giving 148X. If I remember rightly it took 20 sketches of Mars to enable me to complete it. The southern hemisphere was tilted towards us back then just as it is this year. My 2016 map took 36 observations to complete and shows the northern hemisphere in more detail than the 2003 map. I've also made a number of Mars globe's to help with identifying features as seen through the telescope.

Below is the 2003 map showing south top, followed by one of my Mars globe's from the 2016 apparition showing north top e/w reversed.

Edited August 10, 2020 by mikeDnight

[procky1845]

7 minutes ago, mikeDnight said:

I agree it is often quite difficult to interpret maps of Mars and relate the markings to the real life view through the telescope. For that reason I decided to make maps of my own based on observations I made at the eyepiece, rather than having to struggle along trying to flip images in my mind. Also, the view at the eyepiece is often far different from that of the maps.  My first map was drawn in 2003 using a 5" refractor.but I didn't use a diagonal so it's south at the top. Mars back then was 25 arc seconds and high in the sky, and I made all my observations using a 7mm Nagler giving 148X. If I remember rightly it took 20 sketches of Mars to enable me to complete it. The southern hemisphere was tilted towards us back then just as it is this year. My 2016 map took 36 observations to complete and shows the northern hemisphere in more detail than the 2003 map. I've also made a number of Mars globe's to help with identifying features as seen through the telescope.

Below is the 2003 map showing south top, followed by one of my Mars globe's from the 2016 apparition showing north top e/w reversed.

Wow, the detail on your maps and the globe are amazing. I've never even heard of people making their own globes before, very impressive!