APOD: Moons at Opposition (2014 Oct 10)

Comments and questions about the APOD on the main view screen.
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APOD: Moons at Opposition (2014 Oct 10)

Post by APOD Robot » Fri Oct 10, 2014 4:07 am

Image Moons at Opposition

Explanation: From the early hours of October 8, over the Santa Cruz Mountains near Los Gatos, California, the totally eclipsed Moon shows a range of color across this well-exposed telescopic view of the lunar eclipse. Of course, a lunar eclipse can only occur when the Moon is opposite the Sun in Earth's sky and gliding through the planet's shadow. But also near opposition during this eclipse, and remarkably only half a degree or so from the lunar limb, distant Uranus is faint but easy to spot at the lower right. Fainter still are the ice giant's moons. To find them, slide your cursor over the image (or just follow this link) to check out a longer exposure. While even the darkened surface of our eclipsed Moon will be strongly overexposed, Uranus moons Titania, Oberon, and Umbriel can just be distinguished as faint pinpricks of light.

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Nitpicker » Fri Oct 10, 2014 9:36 am

Very nice APOD. I wonder if anyone in eastern Siberia managed to record the eclipsed Moon occulting Uranus?

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Ray-Optics » Fri Oct 10, 2014 1:43 pm

Notice that Uranus is not circular. It looks to be in gibbous phase, but that cannot be because it's in virtually the same direction as the moon in opposition. No, this is an aberration caused by the optics of the telescope itself, and is of course most prevalent at the edges of the field.

Scarlly

Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Scarlly » Fri Oct 10, 2014 4:11 pm

Ray-Optics wrote:Notice that Uranus is not circular. It looks to be in gibbous phase, but that cannot be because it's in virtually the same direction as the moon in opposition. No, this is an aberration caused by the optics of the telescope itself, and is of course most prevalent at the edges of the field.
It looks like all of the stars and planets (except Luna) in the normally exposed photo are oblate but in the heavily exposed photo they look round. Perhaps an artifact caused by tracking the moon alone?

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Ann » Fri Oct 10, 2014 6:20 pm

I like the colors of the picture. The Moon is suitably red. Uranus, how nice to see it here, is blue-green and possibly somewhat overexposed. To the upper right of Uranus is double star HD 5130. They look like a very blue pair, but they are actually F-type stars with a B-V index of about 0.45. This makes them bluer than the Sun, but much yellower than, say, Sirius, Vega or Rigel. How interesting to see them look so blue here.

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Ron-Astro Pharmacist » Fri Oct 10, 2014 8:43 pm

Ann wrote:I like the colors of the picture. The Moon is suitably red. Uranus, how nice to see it here, is blue-green and possibly somewhat overexposed. To the upper right of Uranus is double star HD 5130. They look like a very blue pair, but they are actually F-type stars with a B-V index of about 0.45. This makes them bluer than the Sun, but much yellower than, say, Sirius, Vega or Rigel. How interesting to see them look so blue here.

Ann
Thanks Ann ! I was curious about them too but didn't want to ask. Appreciate you ID'ing them for us.

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Nitpicker » Fri Oct 10, 2014 9:40 pm

Ray-Optics wrote:Notice that Uranus is not circular. It looks to be in gibbous phase, but that cannot be because it's in virtually the same direction as the moon in opposition. No, this is an aberration caused by the optics of the telescope itself, and is of course most prevalent at the edges of the field.
Due to its brightness relative to its size, Uranus appears in this APOD much bigger than its actual angular size:
uranus_and_moons.PNG
It has effectively been imaged in the APOD as a point source of light, and shows a little lens distortion and diffraction artefacts. But if it were resolved as a disc, it is so far away as to never appear gibbous, no matter the time of year (although it is close to opposition at the moment).
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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Boomer12k » Fri Oct 10, 2014 11:33 pm

Interesting notion.....

I doubt, if the Earth's shadow, spread out that far,...if there would be any noticeable effect on Uranus's brightness,...or would it be too diffuse?

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Nitpicker » Fri Oct 10, 2014 11:57 pm

Boomer12k wrote:Interesting notion.....

I doubt, if the Earth's shadow, spread out that far,...if there would be any noticeable effect on Uranus's brightness,...or would it be too diffuse?

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From Uranus, the Earth and Moon appear much smaller than the Sun. I imagine it would be much harder to detect any reduced brightness of Uranus from Earth (as Uranus passes into the Earth's shadow), than it would to detect the reduced brightness of the Sun from Uranus.

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by LocalColor » Sat Oct 11, 2014 1:14 am

Thanks to the APOD now we know the little blue dot in our eclipse photo is Uranus. Fantastic sky here in central Idaho, got to see nearly the entire eclipse.

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Nitpicker » Sat Oct 11, 2014 2:53 am

Nitpicker wrote:
Boomer12k wrote:Interesting notion.....

I doubt, if the Earth's shadow, spread out that far,...if there would be any noticeable effect on Uranus's brightness,...or would it be too diffuse?

:---[===] *
From Uranus, the Earth and Moon appear much smaller than the Sun. I imagine it would be much harder to detect any reduced brightness of Uranus from Earth (as Uranus passes into the Earth's shadow), than it would to detect the reduced brightness of the Sun from Uranus.
Actually, on further investigation, even though the eclipsed Moon occulted Uranus from around eastern Siberia, neither the Earth nor the Moon transited the Sun from Uranus. Both missed by about 1.5 arcmin (with the Sun about 1.5 arcmin in diameter from Uranus).

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by DavidLeodis » Sat Oct 11, 2014 6:36 pm

As nobody else has asked I assume I am the only registered member that has seen this APOD who does not know. What please is the TYC 18 1196 that is labelled in the annotated version that is brought up on moving a cursor over the APOD image (or using the link in the explanation) :?:

I have tried a search but (unless I crawl through very many pages of results) I have not been able to find what it is. I doubt it is a 'signal lamp front passenger side/driver' for a Chevrolet Van that was the main item found in the search results! :P.

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by Chris Peterson » Sat Oct 11, 2014 6:59 pm

DavidLeodis wrote:As nobody else has asked I assume I am the only registered member that has seen this APOD who does not know. What please is the TYC 18 1196 that is labelled in the annotated version that is brought up on moving a cursor over the APOD image (or using the link in the explanation) :?:
It's a star, given here a somewhat incorrect Tycho catalog designation (should really be TYC 18-1196-1). Details.
Chris

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Re: APOD: Moons at Opposition (2014 Oct 10)

Post by DavidLeodis » Sat Oct 11, 2014 8:32 pm

Thank you Chris for your reply which is appreciated :).