Earthshine: The Old Moon in the New Moon’s Arms :)

Earthshine: The Old Moon in the New Moon’s Arms 🙂

☆ Earthshine is the glow that lights up the dark part of the moon. It comes from sunlight reflected off the earth. Leonardo da Vinci described it 500 years ago, realizing that both the earth and the moon are lit by the sun. Earthshine is most intense in the Northern spring (starting now). Astronomers study Earth’s “albedo” (the technical term for reflectivity) to gauge changes in cloud cover and climate.

☆ This picture was taken on Nowruz, the March 20 equinox,from Esfahan, Iran, planet Earth, and is today’s Astronomy Picture of the Day.

For more APOD pictures:

H/T to Bill Noble for sharing the link! Coincidentally, Laura Gibbs just posted the fable of Selene and Endymion. “Selene is the Greek word for “moon,” and Endymion was her lover.” To see a lovely image, and a beautiful Keats quote, go to:

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51 Responses to Earthshine: The Old Moon in the New Moon’s Arms :)

  1. Rajini Rao says:

    Coincidentally, Laura Gibbs posted the fable of Selene and Endymion. “Selene is the Greek word for “moon,” and Endymion was her lover.” To see a lovely image, and a beautiful Keats quote, go to:

  2. Rajini Rao says:

    LOL, Martin Sacha , delighted to play Cupid in any way 🙂

  3. Wow, It is like Lunar eclipse

  4. Rajini Rao says:

    Sekar Sundaram , pretty cool, right? It’s just the crescent of the new moon.

  5. Matt Kuenzel says:

    This is what I’m wondering: when did people first know that moonlight is reflected sunlight?

  6. Rajini Rao says:

    Matt Kuenzel According to this page: Leonardo da Vinci understood this 500 years ago. Does it go back further, is the question.

  7. Matt Kuenzel says:

    Wow, he also wrote that the “ghostly glow” of the whole moon within the crescent moon was caused by light reflected from earth’s oceans. (written 1506 – 1510)

  8. Rajini Rao says:

    Very that’s why Earthshine is also referred to as da Vinci glow!

  9. Matt Kuenzel says:

    Cool, I’ve never heard that term.

  10. Matt Kuenzel says:

    Maybe a silly question but, does the orientation of the crescent (the direction it “faces”) depend on the observer’s position on earth? I’m guessing it must.

  11. Mark Hogan says:

    This was my view driving home this evening 🙂

  12. Rajini Rao says:

    Is that true, Feisal Kamil ? I’ve read that the apparent size of the moon simply depends on it’s relation to the horizon, something known as moon illusion. I found this answer re. the appearance near tropics:

    Matt Kuenzel , Wiki to the rescue! “The orientation of the Moon’s crescent also depends on the latitude of the observation site: close to the equator, an observer can see a smile-shaped crescent Moon.[91]: From,

  13. Matt Kuenzel says:

    OK, that makes sense. I’ll have to pay attention next time I see the crescent moon!

  14. Joey Rodman says:

    Ah! I saw this tonight and commented on it and everyone else thought I was CRAZY. I was right though! Thanks!

  15. Rajini Rao says:

    Joey Rodman , you go set them straight now! 🙂

  16. Suhasitha S says:

    Interesting! But, will somebody say why the Earth fails to lit her pretty satellite on a New moon day?

  17. So after all it probably wasn’t just my imagination. When I was a child I often would swear that I could discern the dark side of the Moon (not to be confused with the hidden side, as we call it in my country) out of the black background, my relatives disdained my claims arguing that the dark side couldn’t reflect any light, so I was fooling myself.

  18. Joey Rodman says:

    Feisal Kamil I think they want to know why we can see the reflection sometimes but other times (new moon specifically) we can’t. I assume it’s to do with the angle we’re looking and shadows but I could be very wrong!

  19. Feisal Kamil, I can understand Sushasitha S’s question perfectly. She’s asking why this phenomenon doesn’t also occur during New Moon, when the Earth can reflect even more light on the dark side of the Moon.

  20. Perhaps it’s due to the presumed fact that during the new moon phase the Moon is only in the sky (although invisible) during the day (but not at night) so we have too much light in the sky to see the faint reflection of the Earth projected on the Moon.

  21. Rajini Rao says:

    Thanks for the Rush contribution, Feisal Kamil 🙂 That was a good one.

  22. I think it should more aptly be the old moon in the new moon’s arms, don’t you think?

  23. Rajini Rao says:

    Kevin Bourrillion , I had exactly the same thought when I posted, but that was the caption on the APOD image! So I checked..I think the APOD image has the caption reversed 🙂 Here is the excerpt from
    “It’s also known as the Moon’s “ashen glow” or “the old Moon in the New Moon’s arms.”

  24. and that version does have almost 2x as many google hits, too. Hmm.

  25. Rajini Rao says:

    Kevin Bourrillion , thanks for the catch (see my edited comment). I’m going to edit the title of the post as well. I can’t edit the caption on the image for some reason.

    P.S. I’m continually delighted by the corrections that pop up from my posts, thank you!

  26. Rajini Rao Matt Kuenzel Alhazen (965 – 1040 ) named Ptolemaeus Secundus (“Ptolemy the Second”) was the first to say that the moon reflects sunlight. He also answered some of your questions related to optics. Take a look :

  27. Rajini Rao says:

    That’s remarkable information, Fadia Lekouaghet , thanks!

  28. My pleasure Rajini Rao 🙂

  29. Matt Kuenzel says:

    Wow Fadia Lekouaghet Alhazen was the man! How did he find time to contribute to all those areas of science? His scientific philosophy sounds like much later scientists: “Therefore, the seeker after the truth is not one who studies the writings of the ancients and, following his natural disposition, puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them, the one who submits to argument and demonstration, and not to the sayings of a human being whose nature is fraught with all kinds of imperfection and deficiency. Thus the duty of the man who investigates the writings of scientists, if learning the truth is his goal, is to make himself an enemy of all that he reads, and, applying his mind to the core and margins of its content, attack it from every side. He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either prejudice or leniency.”

    Now it’s got me thinking, is a completely new moon even possible (a moon that reflects no light at all towards the earth)? It seems that either the moon is exactly between earth and sun (an eclipse) or there must be some point on the moon that receives light from the sun and also is visible from the earth.

  30. I bet Eratosthenes in the 3rd century BC already knew that the light that came from the Moon was actually reflected sunlight. After all, he used the length of the shadows at different latitudes to estimate the size of the circumference of the Earth, and he probably also calculated the distance between the Earth and the Sun. It’s hard to believe that he hadn’t realized that the clear side of the Moon is always pointing at the Sun, since he was familiarized with what shadows look like on the surface of astral bodies like the Earth.

  31. Kevin Bourrillion: “I think it should more aptly be the old moon in the new moon’s arms, don’t you think?”

    May I ask why so?

    “and that version does have almost 2x as many google hits”

    2x as many Google hits may also be wrong. You’d better count the number of scholarly and authoritative references.

  32. Suhasitha S says:

    We have got documentary evidence that the human race started watching celestial objects including the Moon 3000 years ago or so. (Vedic and ancient Astrological literature of India which are supposed to have occurred around 10th century B.C, contain primitive but descriptive such details). To my knowledge, from that period to till date nobody has seen a New Moon lit by the Earth/Sea water (in the absence of at least a tiny piece of moon). So, I genuinely believe that the reason for the visibility of the Earth’s shadow (Old moon) “in the new Moon’s arms” is some thing different.

  33. Rajini Rao says:

    Zephyr López Cervilla , when you look at the image, the new moon (bright white crescent) has arm-like extensions that appear to surround and embrace the old moon (darker spheroid). It doesn’t make sense the other way, does it?

  34. Rajini Rao, the new moon isn’t bright, the new moon is the dark moon. It’s called new just because they chose to arbitrarily start the cycle at that point, like the New Year, which isn’t the brightest moment of the year, either (at least not so in the Northern Hemisphere). In fact, it seems that there used to be the tendency to start the cycles at the darkest point to reach the brightest at the middle of it: the lunar month, the year, and the day (noon corresponds to the middle of the day.)

  35. mada rina says:

    miss Rajini Rao is it a beautiful moon 🙂

  36. Rajini Rao says:

    Zephyr López Cervilla according to Wiki (, “The original meaning of the phrase new moon was the first visible crescent of the Moon”. Also, “The new moon in its original meaning of first crescent marks the beginning of the month in lunar calendars such as the Muslim calendar, and in lunisolar calendars such as the Hebrew calendar, Hindu calendars, and Buddhist calendar.”

  37. Rajini Rao, according to that same Wikipedia article for the Astronomical calendar (and also the Chinese calendar) the new moon is the dark moon. There’s no mention of the Roman calendar.

    However, There’s a couple of details that deserve to be commented. In all that section of the article there isn’t a single reference, including that part about what originally meant new moon (BTW, did originally mean that for the Chinese?). And the second question is, was Da Vinci the person who gave this phenomenon its mame? if so, what calendar did he have in mind when he gave that name, the astronomical or the Jewish/Islamic calendar? So what could be really enlightening is to learn when and who gave that name to the phenomenon, and what name was actually used.

  38. Rajini Rao says:

    I think what the Wiki article is distinguishing that currently we use the term new moon for “no moon”, but that the waxing crescent is the stage immediately following the dark phase, so it is also referred to as the new moon. Assuming that one has time and interest (which I do not, sorry), it should be possible to dig out references to various historical calendars. To which name do you refer? Earthshine?

  39. Rajini Rao Matt Kuenzel Zephyr López Cervilla I suggest to think as in any benchmark, the start is equal to 0 and 0 is by somewhat “nothing”.So new moon = no moon….That said, the question remains placed … “0” is it a materializable value or does it simply means an absence of existing?! :S

    Zephyr López Cervilla To my knowledge, Eratosthenes work was not wearing on moon reflections but rather on measurement of objects sizes and distances between them. He used for this purpose a new technique which consisted of measuring objects shadows. By this method, he also determined that the Earth is spherical in shape. But in all of this, he never predicted anything about the moon radiation.

  40. Matt Kuenzel says:

    Fadia Lekouaghet The moon never gets to a point at which exactly 0 light reflects from the sun. So we should call new moon “min moon” and full moon “max moon” !?!

    This is one explanation: The disk of the moon can appear 100 percent sunlit from Earth only if it is diametrically opposite to the sun in the sky. But at that moment the moon would be positioned in the middle of Earth’s shadow — and in total eclipse. So in any month when there is no eclipse, there is an ever-so-slight sliver of darkness somewhere on the lunar limb throughout those hours — or that moment — when the moon is passing through “full” phase.


  41. Matt Kuenzel says:

    Pop quiz: How many nations feature the crescent moon symbol on their national flags?

  42. Rajini Rao says:

    Matt Kuenzel , I’m guessing Islamic nations, say half a dozen?

  43. Rajini Rao says:

    Lunar trivia : the word lunatic “derives ultimately from latin luna, moon, from the once held belief that lunacy or madness depended on the phases of the moon”.

  44. Matt Kuenzel says:

    Half right! There are 12 nations that have a crescent moon on their flags and one US state, South Carolina (why?)

    (oops correction: it’s 13, I forgot that Libya has a new flag.)













  45. Rajini Rao says:

    Wow, that many..I would not have guessed some..Maldives and Singapore, for example. SC state flag has a crescent moon?

  46. Fadia Lekouaghet, the comment about Eratosthenes was just a guess. After 2,200 years the information about his discoveries and his model of the Universe is probably rather fragmentary, but it seems logical that someone who figured that the Earth was spherical and who measured its size based on the shadows projected on the Earth surface could be inspired by the shape of the Moon as a model of sphericity. What else could have inspired him? Venus phases? These are indistinguishable with the unaided eye. The only spherical object on hand was the Moon.

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