APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

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APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby APOD Robot » Fri Sep 13, 2013 4:09 am

Image Crescent Moon Meets Evening Star

Explanation: On September 8, brilliant planet Venus appearing as the evening star stood near a slender, crescent Moon at sunset. The close celestial pairing or conjunction was a scene enjoyed by skygazers around the world. But from some locations in South America, the Moon actually passed in front of Venus in a lunar occultation. Captured near Las Cañas, Uruguay, this two frame mosaic telescopic view shows the Moon and Venus before and after the occultation. The silvery evening star appears at right just before it winked out behind the dark lunar limb, still in bright twilight skies. About an hour later Venus emerged (left) along the three day old Moon's sunlit edge.

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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby geckzilla » Fri Sep 13, 2013 4:21 am

If a transit is a mini-eclipse, is an occultation a mega-eclipse?
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby Guest » Fri Sep 13, 2013 5:12 am

This picture threw me for a loop - just for a minute! Three day old crescent moon? Forming the shape of a C while it's still waxing? Whatever happened to Luna Mendox?

Luna Mendox is Latin for "The Moon is a Liar": it always forms the shape of a D while it is waxing (Crescens), and it forms the shape of a C while it is waning (Decrescens). And here's the Moon being truthful!

Then I realized - oh, Uruguay. I'd never thought about it, but in the southern hemisphere the C and D shapes would be reversed.

Luna Veracem.

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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby Boomer12k » Fri Sep 13, 2013 8:46 am

Neat....

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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby neufer » Fri Sep 13, 2013 11:38 am

geckzilla wrote:
If a transit is a mini-eclipse, is an occultation a mega-eclipse?

Probably a maxi-eclipse. (Mega is the opposite of micro.)
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby neufer » Fri Sep 13, 2013 11:57 am

Click to play embedded YouTube video.

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Guest wrote:
This picture threw me for a loop - just for a minute! Three day old crescent moon? Forming the shape of a C while it's still waxing? Whatever happened to Luna Mendox?

Luna Mendox is Latin for "The Moon is a Liar": it always forms the shape of a D while it is waxing (Crescens), and it forms the shape of a C while it is waning (Decrescens). And here's the Moon being truthful!

Then I realized - oh, Uruguay. I'd never thought about it, but in the southern hemisphere the C and D shapes would be reversed.

Luna Veracem.
Last edited by neufer on Fri Sep 13, 2013 3:29 pm, edited 2 times in total.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby MadMan » Fri Sep 13, 2013 11:58 am

Thanks Guest! I was stuck on a similar question: why was the Moon moving to the right past Venus instead of to the left? Same answer: southern hemisphere.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby EvilKirk » Fri Sep 13, 2013 1:19 pm

But what of Lazarus? What of Lazarus?
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby jlw » Fri Sep 13, 2013 2:53 pm

Not withstanding the comments and explainations above, I believe this photo is up-side-down. Whether north or south of the equator, the moon still transits the background stars from west to east. Being an evening event, Venus would first be visible in front of (east of) the moon and exit behind (or west) of the moon. This picture would make more sense if inverted.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby walker1001 » Fri Sep 13, 2013 2:57 pm

APOD Robot wrote:Image Crescent Moon Meets Evening Star

Explanation: On September 8, brilliant planet Venus appearing as the evening star stood near a slender, crescent Moon at sunset. The close celestial pairing or conjunction was a scene enjoyed by skygazers around the world. But from some locations in South America, the Moon actually passed in front of Venus in a lunar occultation. Captured near Las Cañas, Uruguay, this two frame mosaic telescopic view shows the Moon and Venus before and after the occultation. The silvery evening star appears at right just before it winked out behind the dark lunar limb, still in bright twilight skies. About an hour later Venus emerged (left) along the three day old Moon's sunlit edge.

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In the picture description right and left are reversed. If they don't get it right we could be left with difficulties in other pictures. Luckily this one is so easy to see that we are left with no doubt how to put things right. :D
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby walker1001 » Fri Sep 13, 2013 3:03 pm

jlw wrote:Not withstanding the comments and explainations above, I believe this photo is up-side-down. Whether north or south of the equator, the moon still transits the background stars from west to east. Being an evening event, Venus would first be visible in front of (east of) the moon and exit behind (or west) of the moon. This picture would make more sense if inverted.


And that way everything would be put right and not left[/i in a mess.[i]Right??
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby geckzilla » Fri Sep 13, 2013 3:05 pm

jlw wrote:Not withstanding the comments and explainations above, I believe this photo is up-side-down. Whether north or south of the equator, the moon still transits the background stars from west to east. Being an evening event, Venus would first be visible in front of (east of) the moon and exit behind (or west) of the moon. This picture would make more sense if inverted.


Would it? Here is a simulated view of the moon, including the horizon, as viewed from Uruguay after Venus has emerged from behind the moon. The red line is the orbital path of Venus.
moonfromuruguay.jpg


walker1001 wrote:In the picture description right and left are reversed. If they don't get it right we could be left with difficulties in other pictures. Luckily this one is so easy to see that we are left with no doubt how to put things right. :D


Are you sure about that? The description seems correct to me.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby geckzilla » Fri Sep 13, 2013 3:15 pm

neufer wrote:
geckzilla wrote:
If a transit is a mini-eclipse, is an occultation a mega-eclipse?

Probably a maxi-eclipse. (Mega is the opposite of micro.)


Mega sounds better, though. Maxi reminds me too much of feminine hygiene products.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby neufer » Fri Sep 13, 2013 3:39 pm

geckzilla wrote:
neufer wrote:
geckzilla wrote:
If a transit is a mini-eclipse, is an occultation a mega-eclipse?

Probably a maxi-eclipse. (Mega is the opposite of micro.)

Mega sounds better, though. Maxi reminds me too much of feminine hygiene products.

How about a midi-eclipse then :?:
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby luigi » Fri Sep 13, 2013 4:29 pm

Thinking about left and right in different hemispheres can get you dizzy.

Both the Moon and Venus set while moving to the left in the south hemisphere.
But the Moon apparently moves to the right with respect to the background stars.
So Venus seems to move from right to left if you take the Moon as a reference.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby BMAONE23 » Fri Sep 13, 2013 4:39 pm

neufer wrote:
geckzilla wrote:
If a transit is a mini-eclipse, is an occultation a mega-eclipse?

Probably a maxi-eclipse. (Mega is the opposite of micro.)

Not to pick nits but I thought that Macro was the opposite of Micro
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby Beyond » Fri Sep 13, 2013 5:51 pm

The 'Truth' is out there somewhere. It's just covered up by all those damn nits :!:
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby neufer » Fri Sep 13, 2013 6:27 pm

BMAONE23 wrote:
neufer wrote:
geckzilla wrote:
If a transit is a mini-eclipse, is an occultation a mega-eclipse?

Probably a maxi-eclipse. (Mega is the opposite of micro.)

Not to pick nits but I thought that Macro was the opposite of Micro

    Just so long as the nits aren't too big.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby Anthony Barreiro » Fri Sep 13, 2013 6:27 pm

luigi wrote:Thinking about left and right in different hemispheres can get you dizzy.

Yes, it can. But it's fun.

Both the Moon and Venus set while moving to the left in the south hemisphere.
But the Moon apparently moves to the right with respect to the background stars.
So Venus seems to move from right to left if you take the Moon as a reference.

Thanks Luigi, your explanation is clear and helpful to me. It's also a bit dizzying to remember the relative motions of the Earth, Moon, and planets!

The first thing I noticed about this image was that the Moon appears "upside down" compared to how I usually see her in the sky, with Mare Crisium toward the bottom rather than the top. Then I read that the picture was taken in Uruguay and figured out that the northern limb of the Moon is toward the bottom as seen from the southern hemisphere, rather than toward the top as I see her from the northern hemisphere.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby walker1001 » Fri Sep 13, 2013 8:35 pm

walker1001 wrote:In the picture description right and left are reversed. If they don't get it right we could be left with difficulties in other pictures. Luckily this one is so easy to see that we are left with no doubt how to put things right. :D


Are you sure about that? The description seems correct to me.[/quote]

You're quite right!!!

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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby Diana » Fri Sep 13, 2013 10:35 pm

Aaaand if they used a right-angle but had it turned to the right, or left side of the tube, would it the inverted image appear as moving in the wrong direction? I could mess with you some more on this, but no.

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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby DavidLeodis » Sat Sep 14, 2013 12:40 pm

I'm not very good at picturing the change in view between the northern and southern hemispheres so I wonder how the occultation would have looked when seen from the Equator. Which way would Venus seem to move relative to the Moon? I'm :?
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby Chris Peterson » Sat Sep 14, 2013 1:49 pm

DavidLeodis wrote:I'm not very good at picturing the change in view between the northern and southern hemispheres so I wonder how the occultation would have looked when seen from the Equator. Which way would Venus seem to move relative to the Moon? I'm :?

Occultations always move the same way, and they look the same from either hemisphere. The Moon moves eastward with respect to the background stars (and planets)... no matter which hemisphere you are in. The Moon has a north, south, east, and west limb, and they look the same no matter which hemisphere you are in. It is common to be facing south when viewing or photographing the Moon in the northern hemisphere, and north when doing so from the southern hemisphere. But there are common exceptions to that, especially when the Moon is near a horizon.

This is why terms like "left", "right", "above", and "below" are usually very poor choices when viewing astronomical images without referents for these relative concepts.

Regardless of which hemisphere you are in, an occultation when the Moon is near the eastern horizon will appear to reappear "above" the Moon. Near the western horizon, it will reappear "below" the Moon. For higher events, it will reappear "right" of the Moon if you are facing south, and "left" of the Moon if you are facing north. Instead of imagining how it might look while standing in a different hemisphere, imagine it from the perspective of lying on the ground, with your head in the same direction regardless of hemisphere.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby neufer » Sat Sep 14, 2013 2:01 pm

DavidLeodis wrote:
I'm not very good at picturing the change in view between the northern and southern hemispheres so I wonder how the occultation would have looked when seen from the Equator. Which way would Venus seem to move relative to the Moon? I'm :?

Forget left/right for the moment.

The orbiting moon is always moving slowly (monthly) in the opposite direction
from its apparent daily motion (which is why tides come later each day).

Hence, the moon always rises slower than every thing else (including Venus)
and the moon also sets slower than every thing else (including Venus).

In the Northern Hemisphere the ecliptic passes to the South of one's head such that
the apparent daily motion of Sun, Moon and planets is from left to right.

In the Southern Hemisphere the ecliptic passes to the North of one's head such that
the apparent daily motion of Sun, Moon and planets is from right to left.

But the apparent daily motion of Moon is always slower than
the Sun, planets AND STARS regardless of where the Earthly observer is.
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Re: APOD: Crescent Moon Meets Evening Star (2013 Sep 13)

Postby DavidLeodis » Sat Sep 14, 2013 2:04 pm

Thanks Chris and neufer for your help, which is appreciated. :)
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