APOD: Antarctic Analemma (2015 Sep 23)

Comments and questions about the APOD on the main view screen.
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neufer
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Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by neufer » Thu Sep 24, 2015 2:13 am

Mikado wrote:
Why is the Sun different sizes? Sep 30 being the smallest.
All of the solar images are overexposed and larger than the sun's actual size.

The smaller suns are probably partially obscured by haze/cloud and thus closer to actual size.
Art Neuendorffer

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Joe Stieber
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Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by Joe Stieber » Thu Sep 24, 2015 2:55 am

Mikado wrote:Why is the Sun different sizes? Sep 30 being the smallest.
The relatively small disc on September 30th in the picture looks like it's due to considerably less exposure, and therefore shows less distortion than most of the other solar images, which look enlarged due to flaring from overexposure. The position of the September 30th sun also looks a little out of place, as do a few of the other dates, so the analemma loop is a bit lumpy.

Otherwise, the earth's orbit is an ellipse, not a circle, so the distance from the earth to the sun varies, and consequently, the apparent diameter of the sun varies. The earth is at aphelion (farthest from the sun) in early July; that's when the sun appears it's smallest as viewed from earth. Conversely, the earth is at perihelion (closest to the sun) in early January; that's when the sun appears it's largest diameter as viewed from earth.

More here: https://en.wikipedia.org/wiki/Earth's_orbit

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Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by phoenix900 » Mon Sep 28, 2015 8:18 pm

Suggest this and all similar posts be written not as the SUN MOVING, but the EARTH moving.

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Nitpicker
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Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by Nitpicker » Tue Sep 29, 2015 12:26 am

phoenix900 wrote:Suggest this and all similar posts be written not as the SUN MOVING, but the EARTH moving.
I find that to be a relatively ignorant suggestion. :P

Adrianos Golemis

Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by Adrianos Golemis » Thu Oct 08, 2015 3:23 pm

HellCat wrote:So why does there seem to be some asymmetry here? Did the camera stand wobble because of global warming?
The asymmetry is because you cannot keep the camera at a steady location outside for the entire year (as you would usually do to shoot a year-long analemma). Since temperature goes down to -80 degrees Celsius, you can only retrieve the camera after each shot and take extra care to place it at exactly the same position next time. However, even the tiniest slip in this, coupled with the wind that is blowing at times when you shoot are responsible for the wobbling that you notice.

Kind regards,

the photographer.

Adrianos Golemis

Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by Adrianos Golemis » Thu Oct 08, 2015 3:25 pm

Nitpicker wrote:Interesting. I guess that the "4 pm" is based on UT+8.
Indeed, 16:00 local time, that is UTC+8 for Concordia Station, without daylight saving (obviously)!

Adrianos Golemis

Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by Adrianos Golemis » Thu Oct 08, 2015 3:29 pm

neufer wrote:
Mikado wrote:
Why is the Sun different sizes? Sep 30 being the smallest.
All of the solar images are overexposed and larger than the sun's actual size.

The smaller suns are probably partially obscured by haze/cloud and thus closer to actual size.
Exactly, September 30 was a particularly cloudy day and thus the solar disc appears smaller. For the rest of the exposures, they were all made with a limited-capability compact digital camera (as my primary DSLR was fried in the cold!), hence the overexposure that could not be corrected at the time of shooting.

Adrianos Golemis

Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by Adrianos Golemis » Thu Oct 08, 2015 3:34 pm

geckzilla wrote:I think it would be easier for most people to understand the image if they saw all the images (or at least a selection of them) that were combined to create the final composite.
Maybe this can help! https://youtu.be/-p1OTqlx7hU .

Adrianos Golemis

Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by Adrianos Golemis » Thu Oct 08, 2015 3:40 pm

BMAONE23 wrote:
dennisma wrote:These shadows look all wrong. It looks like the sun farther right and behind the camera not right in front.
The shadows are in deed pointing to the left of the image indicating that the sun is off to the right at the time the image was taken. This is likely because the sun Was off to the right at the time the final background image was taken.
The reason for this is that the 23 sun images that have been combined to form the analemma were taken when the Sun was pointing at the camera lens, Probably through a filter so as not to over bake the CCD. The 24th image was taken with the Sun out of the field of view and without the filter so that the background could be exposed without an overexposed sun within the field of view.
Precisely! That's exactly the reason; the background picture was made at a different time of the day than the filtered the solar exposures and they were all put together at the end. The reason for shooting the background at a different time of day is, mainly, the solar reflection you would have in the photo which might also set the natural colors off a bit.

Guest

Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by Guest » Thu Oct 08, 2015 3:43 pm

Indigo_Sunrise wrote:
BMAONE23 wrote:What causes the Red Fire patches to the left of the Analemma?
It looks like LMC and SMC or Red Aurorae but ???

I thought they looked like sprites! 8-)
Sorry to disappoint you both, they are neither the aurora nor Mangellan's Clouds (both of which become invisible even in faint sunlight)! What you see here is some internal reflection of sunlight by the solar filter, on the camera CCD. Again, it wasn't the best camera to shoot with, but since my DSLR fell victim to the extreme conditions of Antarctica, it was the only choice!

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BMAONE23
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Re: APOD: Antarctic Analemma (2015 Sep 23)

Post by BMAONE23 » Fri Oct 09, 2015 3:09 am

Guest wrote:
Indigo_Sunrise wrote:
BMAONE23 wrote:What causes the Red Fire patches to the left of the Analemma?
It looks like LMC and SMC or Red Aurorae but ???

I thought they looked like sprites! 8-)
Sorry to disappoint you both, they are neither the aurora nor Mangellan's Clouds (both of which become invisible even in faint sunlight)! What you see here is some internal reflection of sunlight by the solar filter, on the camera CCD. Again, it wasn't the best camera to shoot with, but since my DSLR fell victim to the extreme conditions of Antarctica, it was the only choice!
The YouTube vid you posted clearly shows the red areas as reflections on different days