by alter-ego » Mon Nov 04, 2019 4:59 am
Chris Peterson wrote: ↑Mon Nov 04, 2019 2:18 am
RocketRon wrote: ↑Mon Nov 04, 2019 1:36 am
I'm not sure what to make of the discussions here of the size of Mars in this APOD photo.
Sure the comet head/nucleus is going to be tiny, but Mars in this telescopic should big enough to be in some detail,
IF THE EXPOSURE TIME HADN'T BEEN STRETCHED OUT to capture the comet
At the view shown, Mars is going to be somewhere in the range of this comparative pic. ???
https://www.agenaastro.com/media/images ... uide_3.jpg
Some of these show the crescent phase of Mars.
While limited by our angle of viewing, it is apparent given the viewing angles sometimes.
https://www.cloudynights.com/uploads/mo ... _thumb.jpg
Again, each pixel in this image spans 7 arcseconds of the sky. Mars spans 6 arcseconds. How do you expect to see anything other than an unresolved point?
The comet, both coma and tail, are much larger than Mars.
To get a better visualization, consider the Hubble image of the 1995, near-opposition Mars case in the first link:
![opo0534f.jpg (28.44 KiB) Viewed 2882 times 700 x 700 pixels](./download/file.php?id=35998&t=1&sid=55a0104f9baefb8ec19fdd5b309e99b7)
- 700 x 700 pixels
It is ~14 arcsec diameter, or 2x larger (rounded up) than Mars' angular size in the APOD. The Hubble image is close to 28 arcsec square equivalent to 4 x 4 pixels in the APOD, but in the (reduced-resolution) Hubble image, Mars has a diameter of 330 pixels!. Now using the same imaging setup as Rolando, a zoomed in view of the 4 x 4 pixels containing an unsaturated, the near-opposition Mars would look like:
![Zoomed-in view](./download/file.php?id=35997&sid=55a0104f9baefb8ec19fdd5b309e99b7)
- Zoomed-in view
- 4x4 Mars.png (16.78 KiB) Viewed 2882 times
You can see, Mars' larger angular size in 1995 doesn't help in Rolando's wider field image, and as Chris stated for the APOD image, only one pixel would be needed to show a well-exposed Mars:
![Zoomed-in view](./download/file.php?id=35996&sid=55a0104f9baefb8ec19fdd5b309e99b7)
- Zoomed-in view
- 3x3 Mars.png (16.67 KiB) Viewed 2882 times
[quote="Chris Peterson" post_id=296721 time=1572833899 user_id=117706]
[quote=RocketRon post_id=296719 time=1572831388]
I'm not sure what to make of the discussions here of the size of Mars in this APOD photo.
Sure the comet head/nucleus is going to be tiny, but Mars in this telescopic should big enough to be in some detail,
IF THE EXPOSURE TIME HADN'T BEEN STRETCHED OUT to capture the comet
At the view shown, Mars is going to be somewhere in the range of this comparative pic. ???
https://www.agenaastro.com/media/images/articles/mars-observing-guide_3.jpg
Some of these show the crescent phase of Mars.
While limited by our angle of viewing, it is apparent given the viewing angles sometimes.
https://www.cloudynights.com/uploads/monthly_04_2018/post-253763-0-42191300-1523864022_thumb.jpg
[/quote]
Again, each pixel in this image spans 7 arcseconds of the sky. Mars spans 6 arcseconds. How do you expect to see anything other than an unresolved point?
The comet, both coma and tail, are much larger than Mars.
[/quote]
To get a better visualization, consider the Hubble image of the 1995, near-opposition Mars case in the first link:
[attachment=0]opo0534f.jpg[/attachment]
It is ~14 arcsec diameter, or 2x larger (rounded up) than Mars' angular size in the APOD. The Hubble image is close to 28 arcsec square equivalent to 4 x 4 pixels in the APOD, but in the (reduced-resolution) Hubble image, Mars has a diameter of 330 pixels!. Now using the same imaging setup as Rolando, a zoomed in view of the 4 x 4 pixels containing an unsaturated, the near-opposition Mars would look like:
[attachment=1]4x4 Mars.png[/attachment]
You can see, Mars' larger angular size in 1995 doesn't help in Rolando's wider field image, and as Chris stated for the APOD image, only one pixel would be needed to show a well-exposed Mars:
[attachment=2]3x3 Mars.png[/attachment]