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Planet ID help?

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#1 Andy Perrin

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Posted 04 August 2018 - 05:38

Perhaps the astrophotographers can help me. The following object was seen at 195 degrees S, from Boston, Massachusetts at 11:50pm or so. It was pretty far above the horizon (maybe 40 degrees?) by the time I photographed it.

I took two full spectrum photos with different lenses. (WB was whatever I last had it set up for, so basically arbitrary.) Camera was Sony APS-C sensor (23.5mm horizontal size, 6000 pixels across).

Sony E 55-210mm, taken at 210mm, F/6.3 0.008" ISO200
Object width around 43 pixels diameter - these images have not been resized, just cropped.
Attached Image: _DSC9017 ambient fullspec SonyE55-210 F6.3 0.008%22 iso200.jpg

Meyer-Optik Gorlitz Telemegor 200mm 180mm F/11 0.005" ISO100
Object width around 31 pixels diameter
Attached Image: _DSC9015 ambient fullspec MeyerOptikGorlitz F11 0.005%22 iso100.jpg

Reportedly Mars was very bright the past few days, and it is 24.25 arcsec tonight. I am getting the following:

Horizontal FOV for my Sony lens/APS-C sensor would be

HFOV = 2*atan(23.5mm/(2*210mm)) = 0.1117882019 rad

This is divided up among 6000 pixels across the image, so each pixel is (0.1117882019 rad)/(6000 px) = 0.00001863136698 rad/pixel = 3.8429 arcsec/pixel

So if Mars is 24.25 arcsec, that means it would be (24.25 arcsec)/(3.8429 arcsec/pixel) = 6.3 pixels across. But the above image is 43 pixels. No planet is that big. So what is going on here?

Edited by Andy Perrin, 12 August 2018 - 22:24.


#2 OlDoinyo

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Posted 04 August 2018 - 16:58

If it was to the right of the moon, I can think of no other answer than Mars, because that is where Mars has been. It is posdible that you are not resolving the disk cleanly for some reason; blurring could certainly make an object appear larger.

#3 Hornblende

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Posted 06 August 2018 - 02:38

Looks like Mars to me.

#4 Andy Perrin

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Posted 06 August 2018 - 04:33

Thanks, guys. It does appear to be Mars. I also checked an astronomy app on my phone which confirmed it. However, I still don't know if I can trust that surface detail. The app showed Mars looking vaguely like the above, but it may be confirmation bias on my part.

#5 Øivind Tøien

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Posted 08 August 2018 - 21:44

Here is a visible spectrum capture of Mars from August 2 at 420mm on the a D7100 (24 Mpix), cropped and up-res'ed 2x. Posistion was in the south-west, lots of chromatic aberrations from the atmosphere due to the position close to the horizon. It was very bright, 1/10 sec exposure at f/7.1, -1.3 stops compensation in post. I did also spot what I think was Saturn at the same time a bit further to the west, but did not make any captures of it. I am surprised by the details in your full spectrum capture, especially since it likely was out of focus, making it bigger. I found that focusing on Mars was tricky, finally found a small star in the bright night as focus target.


Posted Image


Lots of better images here:
http://spaceweatherg....php?title=mars

Edited by Øivind Tøien, 08 August 2018 - 21:48.

Øivind

#6 Andy Perrin

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Posted 08 August 2018 - 22:17

Yeah, the "details" are either optical artifacts or maybe I got lucky and said artifacts provided additional magnification? Yours looks more like what I was expecting. It really should have been only 6 pixels or so, by the above arithmetic, so I would love to know what is going on.

Edited by Andy Perrin, 08 August 2018 - 22:18.


#7 Andrea B.

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Posted 10 August 2018 - 20:58

There are several possibilities: atmospheric effects, lens aberrations, saturation/contrast settings. Probably other stuff !?


Here's the Mars photo I made. Not much to show though. This is an unedited, unresized crop which is 100 x 100 pixels. So my Mars here is approximately 15 pixels wide?
Attached Image: 500_1192marsAsShot.jpg


Screen shot of 1600% enlargement.
Attached Image: enlarge.jpg


I lifted the black sky just a bit to show how there is a spread around the bright light. Clearly there are some chromatic aberration and atmospheric effects at play here.
Attached Image: 500_1192marsSpread.jpg


This is the original 5000 x 3728 px photo resized to 1000 x 667 px. The lens + teleconverter was 700 mm focal length. No where near enough !
Attached Image: 500_119201.jpg
Andrea G. Blum
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#8 Andy Perrin

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Posted 10 August 2018 - 21:43

Andrea, what camera/sensor are you using?

#9 Andrea B.

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Posted 10 August 2018 - 21:54

That was the Nikon D500 + Nikon 200-500/5.6 VR + 2x Teleconverter.
With the teleconverter, wide-open becomes f/8.

The lens could almost always auto-focus on Mars. Some failures due to the teleconverter. That's normal. Auto-focus was impossible when the atmospheric conditions were "wavy". But when the seeing was good, the lens did well at AF.

Without the teleconverter, the lens is sharper of course. Look at this next photo where the largest pinpoint of light is Jupiter. There are 3 close moons and two dots far away on the left. I thought those were two moons on the left, but now I do not think so. I don't know whether that faint dot inbetween is a star or a moon. These kinds of photos aren't so great, but I make them just to mark that "I saw this on that night". I get a thrill seeing moons of Jupiter!! B)
The crop here was rotated to be horizontal. The "axis" in the sky between the left-hand moons dots and Jupiter was more like 45°. I've been meaning to look up what moons were visible that night to confirm this, but have not yet gotten around to it.

Please click this up to the full 1200 px width to see the faint dot in the middle. Resize and conversion to JPG did some harm.
Attached Image: jupiter_20180704shoreCottageSwhME_1143501.jpg


Map of moons for 05 July 2018 at 01:22 UT. I only captured 3 or the 4 Galilean moons.
Attached Image: jupiterMoon07052018_0122UT.jpg
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#10 Andy Perrin

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Posted 10 August 2018 - 22:05

So if I repeat the above calculations with your camera/lens+teleconverter specs, I get 20 pixels for mars (using 24.25 arcsec -- it varies over time) which is pretty close to your measured 15 pixels. I am definitely concluding that mine was way out of focus.

This reminds me so much of the whole canals of mars story!

Edited by Andy Perrin, 10 August 2018 - 22:09.