APOD: Shadows of Mountain and Moon (2024 Jan 22)

[APOD Robot]

Shadows of Mountain and Moon

Explanation: Can the Moon and a mountain really cast similar shadows? Yes, but the division between light and dark does not have to be aligned. Pictured, a quarter moon was captured above the mountain Grivola in Italy in early October of 2022. The Sun is to the right of the featured picturesque landscape, illuminating the right side of the Moon in a similar way that it illuminates the right side of the mountain. This lunar phase is called "quarter" because the lit fraction visible from Earth is one quarter of the entire lunar surface. Digital post-processing of this single exposure gave both gigantic objects more prominence. Capturing the terminator of this quarter moon in close alignment with nearly vertical mountain ridge required careful timing because the Earth rotates once a day.

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[starman1]

I thought it was called "First Quarter" phase because the Moon is 1/4 of the way through its orbit around the Earth since New.

[Chris Peterson]

I thought it was called "First Quarter" phase because the Moon is 1/4 of the way through its orbit around the Earth since New.

Correct. Or 3/4. The caption is incorrect.

[VictorBorun]

just imagine the huge plane through the two parallel terminator lines!
Still Saturn's rings are even larger

[Ann]

I thought it was called "First Quarter" phase because the Moon is 1/4 of the way through its orbit around the Earth since New.

Putting on my Spock ears, I must say that I find the "Quarter" Moon expression illogical anyway. If the Moon is called a "Quarter" because a quarter of its surface is illuminated, why then is it called a "Full Moon" when half of its surface is illuminated?

Anyway. Even though today's APOD is in black and white, even I as the Color Commentator must admit that it is incredibly striking and handsome. The way that the terminator of the Moon seems to form an unbroken line with the "terminator" of the mountain is so elegant, and then, of course, the overall shape of the mountain top makes it look like an arrow perfectly placed to point directly at the Moon! That's some shot!

Disregarding the fact that the picture shows us a half moon - sorry, a "quarter moon" - the picture still reminds me of an upside down version of the cosmic exclamation mark (or question mark!), large somewhat triangular nebula NGC 7822 and small round nebula Sharpless 170:

Shadows of Mountain and Moon. Image Credit & Copyright: Enzo Massa Micon

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NGC 7822: Cosmic Question Mark. Image Credit & Copyright: Yizhou Zhang

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Well, the picture of the Cosmic Question Mark turned out to be quite big, right? Actually, NGC 7822+Sharpless 170 is mostly known as the Cosmic Exclamation mark. Let's have a look at a better Cosmic Question Mark!

JWST NIRCam closeup of Herbig-Haro object HH 46/47, with question mark-shaped galaxy (possibly two or three interacting galaxies) in the background. Credit: NASA/ESA/CSA/Joseph DePasquale (STScI)

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There is a really funny space meme based on this perfect deep-space cosmic question mark:

Dr. Becky reacts to space memes

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See Dr. Becky's video here.


And if you're wondering what humans sent out to aliens, it was two identical Golden Records onboard Voyager 1 and Voyager 2. If any aliens ever find one of them, they may indeed wonder what on earth - or what in space - that thing is supposed to say!

Wikipedia wrote:

The Voyager Golden Records are two identical phonograph records, one of each which was included aboard the two Voyager spacecraft launched in 1977. The records contain sounds and images selected to portray the diversity of life and culture on Earth, and are intended for any intelligent extraterrestrial life form who may find them. The records are a time capsule.

And if you don't remember where the Voyager spacecraft are, they have passed the position of Pluto, but they haven't cleared the Oort Cloud (not by far). They have a ways to go before they can hope to meet any aliens!

Positions of the Voyagers. I don't think that the picture is perfectly up to date, but the positions of the Voyagers will not have changed much. You can see the closest star to our Solar system, Alpha Centauri, at far right, but the Voyagers are not headed for Alpha Centauri or any other particular star. Credit: NASA.

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But, speaking of question marks, the ultimate answer to Life, the Universe and Everything is, as many of us know, 42. Now we just have to figure out what the question is.

42 is the answer, but what's the question?

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The number 42 is, in The Hitchhiker's Guide to the Galaxy by Douglas Adams, the "Answer to the Ultimate Question of Life, the Universe, and Everything", calculated by an enormous supercomputer named Deep Thought over a period of 7.5 million years. Unfortunately, no one knows what the question is. Source: Wikipedia

Hey, don't you know? The question is, How long is a marathon? The answer is 42.16481 kilometers. For you Americans, that's 26 miles and 385 yards, but the Universe doesn't understand miles and yards. So, 42.16481 kilometers. Let's forget about the extra meters, because herein lies the Deep Truth. When you have run 42 kilometers exactly, you are done. That's the answer!

Ann

[teredo]

"Quarter" phase refers to how far along in its orbit the moon is, and certainly NOT to how much of it is illuminated.

https://aa.usno.navy.mil/faq/moon_phase ... ts%20orbit)%20from%20New%20Moon.

This should be obvious from the fact that "full moon" doesn't refer to the entire surface of the moon being illuminated; that would mean the moon would be inside the sun every month once every 29.5 days, which I suspect has happened very rarely.

Hopefully this plainly nonsensical statement in the caption is quickly corrected, so it doesn't get spread around and become a common erroneous belief.

[Pastorian]

But, speaking of question marks, the ultimate answer to Life, the Universe and Everything is, as many of us know, 42. Now we just have to figure out what the question is.

42 is the answer, but what's the question?

---

The number 42 is, in The Hitchhiker's Guide to the Galaxy by Douglas Adams, the "Answer to the Ultimate Question of Life, the Universe, and Everything", calculated by an enormous supercomputer named Deep Thought over a period of 7.5 million years. Unfortunately, no one knows what the question is. Source: Wikipedia

Hey, don't you know? The question is, How long is a marathon? The answer is 42.16481 kilometers. For you Americans, that's 26 miles and 385 yards, but the Universe doesn't understand miles and yards. So, 42.16481 kilometers. Let's forget about the extra meters, because herein lies the Deep Truth. When you have run 42 kilometers exactly, you are done. That's the answer!

Ann

If I recall correctly, in one of the books, maybe the 2nd one, Arthur and Ford discover "The Question" from randomizing scrabble letters: "What is 6 x 7?"

[RJN]

I thought it was called "First Quarter" phase because the Moon is 1/4 of the way through its orbit around the Earth since New.

The designation of "quarter moon" is getting discussion, email and might have historical importance -- so I would like to address it here. I will start by saying that I don't know how this controversy can be definitively resolved. I know the US Naval Observatory website gives information on this, but I don't think they are really the ultimate authority.  The International Astronomical Union (IAU), which does have some naming authority, does not appear to me to clearly address this matter, as yet. However perhaps I missed it -- if someone knows a link where the IAU addresses this, please point this out. 

To be clear,  the original APOD text in question is: 
'This lunar phase is called "quarter" because the lit fraction visible from Earth is one quarter of the entire lunar surface.'

I have now adapted the wording of this APOD on the main NASA APOD page, adding the text "in part" before "because" to make the declaration less definitive.

My logic in writing that sentence was that most of the moon phases, as used in Western culture, are visually descriptive. A "full moon" appears fully lit. There is no time reference in "full moon". Similarly, "crescent moon" is also visually descriptive. As is "gibbous". It therefore seemed (and still seems) logical to me that the phase "quarter" is also visually descriptive, or can be logically interpreted that way. A time qualifier can enter, such as "first quarter", but the temporal nature of the word "first" here does not necessarily, in my opinion, transfer to the second word "quarter". In terms of visual description, the "quarter moon" might be called "half moon", but that term is not used as frequently as "quarter moon". As I indicated in the APOD text, the term "quarter moon" is technically accurate in the sense that at that phase, the fraction of the Moon seen lit from the Earth is actually (nearly) one quarter of the entire lunar surface. 

It might be of interest to astronomical historians if this nomenclature degeneracy can be definitely resolved with good historical references. 

[Chris Peterson]

I thought it was called "First Quarter" phase because the Moon is 1/4 of the way through its orbit around the Earth since New.

The designation of "quarter moon" is getting discussion, email and might have historical importance -- so I would like to address it here. I will start by saying that I don't know how this controversy can be definitively resolved. I know the US Naval Observatory website gives information on this, but I don't think they are really the ultimate authority.  The International Astronomical Union (IAU), which does have some naming authority, does not appear to me to clearly address this matter, as yet. However perhaps I missed it -- if someone knows a link where the IAU addresses this, please point this out. 

To be clear,  the original APOD text in question is: 
'This lunar phase is called "quarter" because the lit fraction visible from Earth is one quarter of the entire lunar surface.'

I have now adapted the wording of this APOD on the main NASA APOD page, adding the text "in part" before "because" to make the declaration less definitive.

My logic in writing that sentence was that most of the moon phases, as used in Western culture, are visually descriptive. A "full moon" appears fully lit. There is no time reference in "full moon". Similarly, "crescent moon" is also visually descriptive. As is "gibbous". It therefore seemed (and still seems) logical to me that the phase "quarter" is also visually descriptive, or can be logically interpreted that way. A time qualifier can enter, such as "first quarter", but the temporal nature of the word "first" here does not necessarily, in my opinion, transfer to the second word "quarter". In terms of visual description, the "quarter moon" might be called "half moon", but that term is not used as frequently as "quarter moon". As I indicated in the APOD text, the term "quarter moon" is technically accurate in the sense that at that phase, the fraction of the Moon seen lit from the Earth is actually (nearly) one quarter of the entire lunar surface. 

It might be of interest to astronomical historians if this nomenclature degeneracy can be definitely resolved with good historical references. 

I will note that my non-astronomer friends, family, and students almost always refer to both a first and third quarter Moon as a "half moon". I would say that colloquially, we usually only hear "new", "half", and "full" (with the first two used whether waxing or waning).