APOD: The Last Days of Venus as the Star... (2022 Jan 06)

[APOD Robot]

The Last Days of Venus as the Evening Star

Explanation: That's not a young crescent Moon posing behind cathedral towers after sunset. It's Venus in a crescent phase. About 40 million kilometers away and about 2 percent illuminated by sunlight, it was captured with camera and telephoto lens in this series of exposures as it set in western skies on January 1 from Veszprem, Hungary. The bright celestial beacon was languishing in the evening twilight, its days as the Evening Star coming to a close as 2022 began. But it was also growing larger in apparent size and becoming an ever thinner crescent in telescopic views. Heading toward a (non-judgemental) inferior conjunction, the inner planet will be positioned between Earth and Sun on January 9 and generally lost from view in the solar glare. A crescent Venus will soon reappear though. Rising in the east by mid-month just before the Sun as the brilliant Morning Star.

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[gmPhil]

"about 2 percent illuminated by sunlight" sounds somewhat strange to me - it is 100% illuminated by sunlight!! I presume you mean that about 2% of the sunlight that hits it is reflected...

[De58te]

"about 2 percent illuminated by sunlight" sounds somewhat strange to me - it is 100% illuminated by sunlight!! I presume you mean that about 2% of the sunlight that hits it is reflected...

I would think (and I am not an expert) that if Venus is directly in line between the Earth and the Sun, that we on Earth would be seeing Venus' night side which isn't illuminated by the Sun. That is that there are presumably no artificial city lights on Venus, and I heard tell that Venus doesn't have a moon like Earth does that would reflect secondary light back on the night side of Venus. Now tell me if this is true, but I think some science fiction story said that the atmosphere is so thick on Venus and light absorbing that it reflects Venus daylight all around to the night side so that its night is as lit up as the day??

[gmPhil]

if Venus is directly in line between the Earth and the Sun,

Pretty sure that's not the case here - we'd have "new Venus" rather than a crescent one. As for the hypothesis in that sci-fi story... I am also no expert but don't think that it's true.

[Dan]

"about 2 percent illuminated by sunlight" sounds somewhat strange to me - it is 100% illuminated by sunlight!! I presume you mean that about 2% of the sunlight that hits it is reflected...

Venus is 50% illuminated by sunlight, always.

However the view from Mercury (at opposition) would be pretty insane.

[Sa Ji Tario]

It is because of this type of discussion that the science of Astronomy is dispersed

[orin stepanek]

Ah; beautiful Venus! I got to wondering, just how much cooler you
are on your night side! The internet says that the night side is about
the same as the day side! The days are about 243 Earth days long!
https://www.msn.com/en-us/news/technolo ... r-BB1gkQo4

[rstevenson]

"about 2 percent illuminated by sunlight" sounds somewhat strange to me - it is 100% illuminated by sunlight!! I presume you mean that about 2% of the sunlight that hits it is reflected...

I’ve always taken that sort of statement as meaning that 2% of the disk of Venus is reflecting sunlight towards us. I may be wrong.

Rob

[Chris Peterson]

"about 2 percent illuminated by sunlight" sounds somewhat strange to me - it is 100% illuminated by sunlight!! I presume you mean that about 2% of the sunlight that hits it is reflected... :)

I’ve always taken that sort of statement as meaning that 2% of the disk of Venus is reflecting sunlight towards us. I may be wrong. :-)

Rob

You are not. It's a reference to phase (not to be confused with phase angle), which as with the Moon or any other body that shows phases, simply refers to the percentage of the disc that is illuminated from the observer's reference (typically the Earth).

[rstevenson]

"about 2 percent illuminated by sunlight" sounds somewhat strange to me - it is 100% illuminated by sunlight!! I presume you mean that about 2% of the sunlight that hits it is reflected...

I’ve always taken that sort of statement as meaning that 2% of the disk of Venus is reflecting sunlight towards us. I may be wrong.

Rob

You are not. It's a reference to phase (not to be confused with phase angle), which as with the Moon or any other body that shows phases, simply refers to the percentage of the disc that is illuminated from the observer's reference (typically the Earth).

Thanks Chris. Clarity as always.

Rob

[neufer]

"about 2 percent illuminated by sunlight" sounds somewhat strange to me - it is 100% illuminated by sunlight!! I presume you mean that about 2% of the sunlight that hits it is reflected...

I’ve always taken that sort of statement as meaning that 2% of the disk of Venus is reflecting sunlight towards us. I may be wrong.

You are not. It's a reference to phase (not to be confused with phase angle), which as with the Moon or any other body that shows phases, simply refers to the percentage of the disc that is illuminated from the observer's reference (typically the Earth).

<<phase (n.) 1705, "phase of the moon, particular recurrent appearance presented by the moon (or Mercury or Venus) at a particular time," back-formed as a singular from Modern Latin phases, plural of phasis, from Greek phasis "appearance" (of a star), "phase" (of the moon), from stem of phainein "to show, to make appear" (from PIE root *bha- (1) "to shine"). Latin singular phasis was used in English from 1660 for each of the aspects of the moon. General (non-lunar) sense of "aspect, appearance, stage of development at a particular time" is attested by 1841. Meaning "temporary difficult period" (especially in reference to adolescents) is attested from 1913.>>

[MarkBour]

Hey cool! Let's point the JWST to get a shot of Venus at inferior conjunction! (sarcasm emoji)

[Chris Peterson]

Hey cool! Let's point the JWST to get a shot of Venus at inferior conjunction! (sarcasm emoji)

Better shoot quick, though, before the boiling clouds of helium obscure the view!

[johnnydeep]

"about 2 percent illuminated by sunlight" sounds somewhat strange to me - it is 100% illuminated by sunlight!! I presume you mean that about 2% of the sunlight that hits it is reflected...

I’ve always taken that sort of statement as meaning that 2% of the disk of Venus is reflecting sunlight towards us. I may be wrong.

Rob

You are not. It's a reference to phase (not to be confused with phase angle), which as with the Moon or any other body that shows phases, simply refers to the percentage of the disc that is illuminated from the observer's reference (typically the Earth).

That's how I took it, but only 2%? I would say the disc looks to be at least 20% illuminated.

[Chris Peterson]

I’ve always taken that sort of statement as meaning that 2% of the disk of Venus is reflecting sunlight towards us. I may be wrong. :-)

Rob

You are not. It's a reference to phase (not to be confused with phase angle), which as with the Moon or any other body that shows phases, simply refers to the percentage of the disc that is illuminated from the observer's reference (typically the Earth).

That's how I took it, but only 2%? I would say the disc looks to be at least 20% illuminated.

Because it's massively overexposed and you're seeing a big blob of scattered light.

[MarkBour]

Hey cool! Let's point the JWST to get a shot of Venus at inferior conjunction! (sarcasm emoji)

Better shoot quick, though, before the boiling clouds of helium obscure the view!

Interesting. I had not read about this! On the Webb, the MIRI instrument is cooled by a special "cryocooler".

Excerpt from: https://webb.nasa.gov/content/about/inn ... ooler.html
The Webb MIRI cryocooler is basically a sophisticated refrigerator with its pieces distributed throughout the observatory. The primary piece is the Cryocooler Compressor Assembly (CCA). It is a heat pump consisting of a precooler that generates about 1/4 Watt of cooling power at about 14 kelvin (using helium gas as a working fluid), and a high-efficiency pump that circulates refrigerant (also helium gas) cooled by conduction with the precooler, to MIRI.

So, you seem to be implying that getting the scope too hot could burst this system, venting helium into space.

[johnnydeep]

You are not. It's a reference to phase (not to be confused with phase angle), which as with the Moon or any other body that shows phases, simply refers to the percentage of the disc that is illuminated from the observer's reference (typically the Earth).

That's how I took it, but only 2%? I would say the disc looks to be at least 20% illuminated.

Because it's massively overexposed and you're seeing a big blob of scattered light.

Ah, ok. Fooled again by optics!