APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

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APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by APOD Robot » Thu Apr 14, 2016 4:12 am

Image Full Venus and Crescent Moon Rise

Explanation: Inner planet Venus and a thin crescent Moon are never found far from the Sun in planet Earth's skies. Taken near dawn on April 6, this timelapse composite shows them both rising just before the Sun. The mountaintop Teide Observatory domes on the fortunate island of Tenerife appear in silhouette against the twilight. In fact, the series of telephoto exposures follows the occultation of Venus by the Moon in three frames. Far from Earth in its orbit and in a nearly full phase, Venus was 96 percent illuminated. Near perigee or closest approach to Earth, the Moon's slender crescent represents about 2 percent of the lunar disk in sunlight. Seen in the first two exposures, the brilliant morning star only vanishes in the third as it winks out behind the bright lunar limb. Five minutes of the dramatic occultation at dawn is compressed into 15 seconds in this timelapse video (vimeo).

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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by saturno2 » Thu Apr 14, 2016 5:07 am

very interesting

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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by starsurfer » Thu Apr 14, 2016 11:49 am

I really like the video and find it a great use of modern resources to record an event that has been observed for many thousands of years! :D

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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by wmccrack » Thu Apr 14, 2016 12:02 pm

Is the writeup in error?

How is it possible that the moon is nearly 0% illuminated and Venus is reported as 96% illuminated when they are adjacent in the sky and illuminated by the same sun?

Nix that question !! :oops:

Venus must be on the FAR side of the sun. :o

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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by Asterhole » Thu Apr 14, 2016 2:31 pm

wmccrack wrote:Is the writeup in error?

How is it possible that the moon is nearly 0% illuminated and Venus is reported as 96% illuminated when they are adjacent in the sky and illuminated by the same sun?

Nix that question !! :oops:

Venus must be on the FAR side of the sun. :o
It was stated that Venus was FAR from the Earth and presumably yes, nearly opposite the Sun from us. It would be the only way we'd see a near-full phase of the planet - and we'd probably see it at its brightest.

Odd though, and I'm sure it's due to the photographic exposure setting, but the one in the middle appears that Venus is in front of the Moon.
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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by Chris Peterson » Thu Apr 14, 2016 2:51 pm

Asterhole wrote:Odd though, and I'm sure it's due to the photographic exposure setting, but the one in the middle appears that Venus is in front of the Moon.
Let's hope not!
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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by neufer » Thu Apr 14, 2016 3:28 pm

Asterhole wrote:
Odd though, and I'm sure it's due to the photographic exposure setting,
but the one in the middle appears that Venus is in front of the Moon.
  • You should see the Video.
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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by leon.l7027@gmail.com » Thu Apr 14, 2016 4:11 pm

What the video clearly shows is that when the moon crescent is that thin, it is the shine and/or thin lunar atmosphere that is lit, and occultation does not occur until Venus goes behind the dark. Or perhaps the thin lunar atmosphere lengthens the "settin" of Venus, as Earth's atmosphere does to the sun and moon.

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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by Chris Peterson » Thu Apr 14, 2016 4:26 pm

leon.l7027@gmail.com wrote:What the video clearly shows is that when the moon crescent is that thin, it is the shine and/or thin lunar atmosphere that is lit, and occultation does not occur until Venus goes behind the dark. Or perhaps the thin lunar atmosphere lengthens the "settin" of Venus, as Earth's atmosphere does to the sun and moon.
There is no lunar atmosphere (or to the extent there is, we're not seeing it). Venus is simply so bright we see scattered and diffracted light around it, which overlaps the edge of the Moon. At the image plane, not in reality.
Chris

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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by Asterhole » Thu Apr 14, 2016 4:45 pm

Chris Peterson wrote: There is no lunar atmosphere (or to the extent there is, we're not seeing it). Venus is simply so bright we see scattered and diffracted light around it, which overlaps the edge of the Moon. At the image plane, not in reality.
My thinking as well. Earth's atmosphere also is probably affecting the shot, so probably a naked-eye would see the same thing...(?) Someone who wasn't as astronomy-savvy who saw it would wonder what's happening on the moon.
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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by geckzilla » Thu Apr 14, 2016 9:46 pm

Chris Peterson wrote:
leon.l7027@gmail.com wrote:What the video clearly shows is that when the moon crescent is that thin, it is the shine and/or thin lunar atmosphere that is lit, and occultation does not occur until Venus goes behind the dark. Or perhaps the thin lunar atmosphere lengthens the "settin" of Venus, as Earth's atmosphere does to the sun and moon.
There is no lunar atmosphere (or to the extent there is, we're not seeing it). Venus is simply so bright we see scattered and diffracted light around it, which overlaps the edge of the Moon. At the image plane, not in reality.
Possibly a good way to show visually how a point source or point-like source isn't actually as big as it appears to be. My attempts to show how small a star is in relationship to a single pixel was perhaps not very fun or easy to understand.
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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by Chris Peterson » Thu Apr 14, 2016 9:57 pm

geckzilla wrote:
Chris Peterson wrote:
leon.l7027@gmail.com wrote:What the video clearly shows is that when the moon crescent is that thin, it is the shine and/or thin lunar atmosphere that is lit, and occultation does not occur until Venus goes behind the dark. Or perhaps the thin lunar atmosphere lengthens the "settin" of Venus, as Earth's atmosphere does to the sun and moon.
There is no lunar atmosphere (or to the extent there is, we're not seeing it). Venus is simply so bright we see scattered and diffracted light around it, which overlaps the edge of the Moon. At the image plane, not in reality.
Possibly a good way to show visually how a point source or point-like source isn't actually as big as it appears to be. My attempts to show how small a star is in relationship to a single pixel was perhaps not very fun or easy to understand.
At the resolution of today's image, Venus (angular size 10 arcsec) should cover 1.5 pixels. In actuality, it covers 8. So most of what we're seeing as Venus in this image is light where Venus isn't.
Chris

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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by geckzilla » Thu Apr 14, 2016 10:07 pm

Yeah, Venus is not smaller than a pixel this time. It would be nice to have a video of a visually oversized star or some such disappear completely behind the moon. Problem is that would require a long exposure. I don't suppose it will ever work unless we just so happen to have a nearby supernova that also happens to pass behind the moon at some point.
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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by Boomer12k » Fri Apr 15, 2016 1:54 am

Cool...

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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by neufer » Fri Apr 15, 2016 2:27 pm

Click to play embedded YouTube video.
There is also something of a time delay afterglow a la the
Apollo XI moonwalk video but this time with the dim new
moon playing the role of the faint foreground moving object.
Chris Peterson wrote:
leon.l7027@gmail.com wrote:
What the video clearly shows is that when the moon crescent is that thin, it is the shine and/or thin lunar atmosphere that is lit, and occultation does not occur until Venus goes behind the dark. Or perhaps the thin lunar atmosphere lengthens the "settin" of Venus, as Earth's atmosphere does to the sun and moon.
There is no lunar atmosphere (or to the extent there is, we're not seeing it). Venus is simply so bright we see scattered and diffracted light around it, which overlaps the edge of the Moon. At the image plane, not in reality.
Art Neuendorffer

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Re: APOD: Full Venus and Crescent Moon Rise (2016 Apr 14)

Post by MarkBour » Fri Apr 15, 2016 4:09 pm

Asterhole wrote:It was stated that Venus was FAR from the Earth and presumably yes, nearly opposite the Sun from us. It would be the only way we'd see a near-full phase of the planet - and we'd probably see it at its brightest.
I would just point out that "brightest" is a complicated matter in the end.
After wandering through a few Wikipedia and space.com articles on it: I've come to understand that there are terms such as luminosity (visual and bolometric), brilliancy, brightness, and magnitude, but I don't quite have them fully sorted out yet. Also, astronomers do not have very many objects they observe that are luminous and large in the sky, so I haven't yet learned any terms for luminosity per unit solid angle. Such a term would be relevant to discussing the Sun, Moon, or Venus, and might be the term that you'd be correct with. (When Venus is near opposition, its disc may be sending more photons to your eye per unit solid angle than at any other time. But even that, I am not at all sure of. Perhaps someone will enlighten me.)

But in most uses of the terms, and in the effect on the eye of a human observer standing on planet Earth, I'd say that Venus is "brightest" when it is a 26-28% crescent, not when it is near full (as the aforementioned articles indicate).
Mark Goldfain