Explanation: A thin, one day old crescent Moon hugged the western horizon after sunset on Monday, December 6. The Moon also occulted or passed in front of Mars. But only some well-placed skygazers along a band through North America were able to catch this lunar occultation's final act in fading twilight. For example, this telephoto image nicely captures the Mars as a pinprick of light, shortly after it emerged from behind the crescent Moon's sunlit edge. The luminous skyview is from De Soto, Kansas in the central US. Of course, this month's upcoming total lunar eclipse will entertain a much wider audience of Moon enthusiasts during the night of December 20/21.
Orin, you read that exactly backwards! All of North America will see this eclipse; it's not visible in most of Africa, India, or Arabia. Great chart; thanks for it!
Re: APOD: A Twilight Occultation (2010 Dec 10)
Posted: Fri Dec 10, 2010 1:40 pm
by Star*Hopper
Quick! - somebody post that e-mail about Mars appearing as big as the Moon!!
Re: APOD: A Twilight Occultation (2010 Dec 10)
Posted: Fri Dec 10, 2010 2:02 pm
by neufer
jeff wrote:
However, that doesn't look like any crescent moon that I've ever seen...is it just me?
Let me know !
Such a very thin crescent setting that close to the horizon in the bright twilight sky
would mostly go unnoticed(; unless, perhaps, one were a Muslim).
Re: APOD: A Twilight Occultation (2010 Dec 10)
Posted: Fri Dec 10, 2010 2:29 pm
by orin stepanek
owlice wrote:Orin, you read that exactly backwards! All of North America will see this eclipse; it's not visible in most of Africa, India, or Arabia. Great chart; thanks for it!
Thanks owlice; I hurry too much sometimes!
It's a neat way to start winter though.
Re: APOD: A Twilight Occultation (2010 Dec 10)
Posted: Fri Dec 10, 2010 3:04 pm
by RADDAD
Great photo! Brings back fond memories of an occultation of Saturn I observed shortly after I had made my first six inch Newtonian (circa 1961/62) back in Indiana. I was able to see the whole show - entrance and exit. My favorite part was the emergence (or disappearance) from the dark limb of the moon because the planetary view was so clean and mysterious.
Re: APOD: A Twilight Occultation (2010 Dec 10)
Posted: Fri Dec 10, 2010 3:22 pm
by owlice
Orin, I had to look twice at it and read the fine print; it's no wonder you read it as you did, given its intuitively reversed design. And yes, a great way to start a season!
<<According to the Yomiuri Shimbun newspaper, the photos were taken with Akatsuki about 600,000 kilometers from Venus. This image is actually good news, although it's little consolation: it's proof positive that the science instruments are healthy. They actually tested three of the cameras: one that takes images in ultraviolet, two in infrared. The images are very similar to the Akatsuki departure shots of Earth, taken less than seven months ago.
It happened that Venus scientist David Grinspoon, who was one of several American co-investigators recently named to be participants on the Akatsuki team, was on Facebook when I saw these images being posted by numerous Japanese space fans. I asked him what he thought about them, and he said, "Well, my initial reaction is that they are poignant and heartbreaking." He went on: "To have a perfectly functioning spacecraft with all those great instruments make it all that way across the depths, and then because of some problem with a 12 minute operation, to go sailing off back into the blackness..."
How beautiful, yet awful!>>
Re: APOD: A Twilight Occultation (2010 Dec 10)
Posted: Fri Dec 10, 2010 10:08 pm
by harold
Okay, this is really bugging me. The caption states that Mars is "just emerging from the sunlit side" of the crescent moon. But if it's evening twilight and the moon is SETTING, how can Mars be emerging BELOW the setting moon? Seems to me that this shot had to be taken just PRIOR to the occultation, not after. Somebody help me out before I get kicked out of the club!
Re: APOD: A Twilight Occultation (2010 Dec 10)
Posted: Fri Dec 10, 2010 10:23 pm
by neufer
harold wrote:Okay, this is really bugging me. The caption states that Mars is "just emerging from the sunlit side" of the crescent moon. But if it's evening twilight and the moon is SETTING, how can Mars be emerging BELOW the setting moon? Seems to me that this shot had to be taken just PRIOR to the occultation, not after. Somebody help me out before I get kicked out of the club!
Mars is setting faster than the waxing moon (which rises higher & gets larger from evening to evening).
Re: APOD: A Twilight Occultation (2010 Dec 10)
Posted: Fri Dec 10, 2010 10:24 pm
by Chris Peterson
harold wrote:Okay, this is really bugging me. The caption states that Mars is "just emerging from the sunlit side" of the crescent moon. But if it's evening twilight and the moon is SETTING, how can Mars be emerging BELOW the setting moon? Seems to me that this shot had to be taken just PRIOR to the occultation, not after. Somebody help me out before I get kicked out of the club!
The Moon moves eastward with respect to the stars. Or, if you prefer, it moves westward at a slower rate than the stars move. Mars is distant enough that it is moving, to a first approximation, at the same rate as the background stars (the sidereal rate). So Mars is setting faster than the Moon is, and therefore is seen coming out of occultation between the Moon's and the Sun's apparent positions on the sky.
Mars entered occultation on the other side of the Moon somewhat earlier.
A Twilight Occultation
with trees' branches around. 
Thanks owlice; I hurry too much sometimes!
