Dark side of the moon

[garyclaytonpalmer]

The Moon is always facing the same side towards the Earth, Right? And usually the other side is always in the dark? But during a eclipse the dark side is towards the Sun and the what is normally lit side becomes darK?
What is the tempertures on the lit side and the dark side? With no atmosphere the moon must be very cold on the dark side and very hot on the light side?

[Chris Peterson]

The Moon is always facing the same side towards the Earth, Right? And usually the other side is always in the dark? But during a eclipse the dark side is towards the Sun and the what is normally lit side becomes darK?

No part of the Moon is usually dark. The Moon goes around the Earth once per month, and its day is one month long. So no matter where you are, you see a two week day and a two week night. Only when we see a full moon is the other side completely in the dark. Half the Moon is always lit.

What is the tempertures on the lit side and the dark side? With no atmosphere the moon must be very cold on the dark side and very hot on the light side?

In the dark, or in the shade, the lunar surface temperature drops lower than -150°C; in the Sun it is over 100°C.

[garyclaytonpalmer]

If thats true then why when I look at the moon even when its only a half or quarter full does whats left in the light look like the same moon when its full? Only missing the shaded part.

[Chris Peterson]

If thats true then why when I look at the moon even when its only a half or quarter full does whats left in the light look like the same moon when its full? Only missing the shaded part.

Because it is the same part. As you noted, the Moon always keeps the same face towards us. Its days and nights have the same cause as ours: it shadows itself on the side away from the Sun. So half is always lit, half is in shadow. When you see a half moon, you're looking at the terminator between day and night. Half of the side you can't see is also illuminated.

[BMAONE23]

This APOD shows the effect pretty well
lunation

[The Code]

nice post, BMAONE23

Tells me, mining experts need to get a move on.. Something solid in that big cheese, that always wants to point to earth.

Mark

[neufer]

What does a Cresent moon represent? (This IS a trick question.)

[apodman]

What does a Cresent moon represent? (This IS a trick question.)

The crescent moon represents the girls' outhouse. The sun represents the boys' outhouse. For reasons unknown, cartoon artists and outhouse door decorators have mistakenly used the crescent moon on any old outhouse.

[Chris Peterson]

What does a Cresent moon represent? (This IS a trick question.) :wink:

The crescent moon represents the girls' outhouse. The sun represents the boys' outhouse. For reasons unknown, cartoon artists and outhouse door decorators have mistakenly used the crescent moon on any old outhouse.

He didn't actually ask what a crescent moon represents (but thanks for the information, all the same <g>).

[apodman]

He didn't actually ask what a crescent moon represents (but thanks for the information, all the same <g>).

Now I see that he was referring to the spelling "Cresent" in the diagram. Apparently incorrect spelling is so rampant in this forum (not in your posts nor mine nor neufer's certainly) that I have learned to read around it.

---

I have no advice for Internet Explorer users, but Mozilla Firefox provides this option:

Tools > Options > Advanced > General > Browsing > Check my spelling as I type

It makes me look like a better typist than I am.

Four yew who spell rite butt ewes the wrong homophone (eye suspect that sum of hue due it purposely as an irreverent stile), the spelling checker will knot help, sew aye guess aisle just half two continue too suffer.

[garyclaytonpalmer]

So the moon does not revolve on its axis but revolves around the earth? It does not turn around but stays with the same side facing the sun all the time?

[apodman]

The moon rotates on its axis in the same amount of time that it takes to revolve around the Earth. So the same side of the moon always faces the Earth. The same side of the moon does not always face the sun. The sun rises and sets once a month on the moon. The phrase "dark side of the moon" is a misnomer if you are talking about actual absence of sunlight. The far side of the moon is only "dark" in the sense of being hidden or secret (definition #13 of "dark" in my dictionary) as it was before we saw it from spacecraft.

[Chris Peterson]

So the moon does not revolve on its axis but revolves around the earth? It does not turn around but stays with the same side facing the sun all the time?

It does not have the same side facing the Sun, it has the same side (approximately) facing the Earth. It rotates on its axis once per month, and it revolves around the Earth once a month. That's why it always keeps the same face towards the Earth. Because it completes one rotation in a month, its day is half of that and its night the other half- two weeks each. If you were anywhere on the Moon (other than a pole) you would see a sunrise, and over two weeks the Sun would cross the sky, then a sunset, then two weeks of night. If you were somewhere on the face towards the Earth, you would not see the Earth change position in the sky, however (except for a bit of wobble). You would see the Earth's rotation, of course, since the Earth doesn't keep the same face towards the Moon. You would also see the Earth go through phases over the month, very similar to the phases of the Moon as seen from Earth (but 180° out of phase).

[apodman]

Maybe the diagram is confusing. Maybe it looks like the same side of the moon is always facing the sun (to the right) because the lit side is always facing the sun (to the right). This is not the case. So I have put a red dot on the middle of the "near side" of the moon. "Near side" and "far side" are the near and far sides of the moon as it is seen from Earth. The red dot always stays in one place on the moon and always faces Earth. It goes in and out of sunlight. The sunlight shown on the right side of the moon is on a different part of the moon in each of the eight phases shown.



When the phase is "New", the sun lights the "far" side of the moon. When the phase is "Full", the sun lights the "near" side of the moon. When the phase is "1st Quarter" or "3rd Quarter", the sun lights half of the near side and half of the far side of the moon.

In your original question, you asked about an eclipse. In a lunar eclipse the moon is Full, but the Earth blocks the sun and casts its shadow on the moon. In a solar eclipse the moon is New, and the moon blocks the sun and casts its shadow on the Earth.

[Chris Peterson]

Maybe the diagram is confusing. Maybe it looks like the same side of the moon is always facing the sun (to the right) because the lit side is always facing the sun (to the right). This is not the case. So I have put a red dot on the middle of the "near side" of the moon. "Near side" and "far side" are the near and far sides of the moon as it is seen from Earth. The red dot always stays in one place on the moon and always faces Earth. It goes in and out of sunlight. The sunlight shown on the right side of the moon is on a different part of the moon in each of the eight phases shown.

To which I'd add, from the dot's perspective,

"New" is midnight
"1st Quarter" is dawn
"Full" is noon
"3rd Quarter" is sunset

[bystander]

There is no dark side of the moon really. Matter of fact it's all dark.

[neufer]

There is no dark side of the moon really. Matter of fact it's all dark.

<<When [New Horizons] get to Pluto, the sun will be shining on the south pole (a.k.a. the north pole, according to some astronomers- the controversy over what to call the two poles of Pluto, which spins on its side, is second only in vigor and meaninglessness to the controversy over whether it's a planet). The north pole (I'm using the official International Astronomical Union definition here) will be in darkness during our brief flyby. That's a shame- we'd really like to see what's going on up there. We expect a lot of nitrogen snowfall during the long polar winter as nitrogen frost burns off the summer hemisphere and transfers to the north, but so far that's just an idea, and we'd love to see whether those winter snowfields really exist. Fortunately the sun isn't the only light source at our disposal- we also have Pluto's moon Charon, which is big and close and thus looms large in Pluto's sky. So we can observe Pluto's north pole by moonlight. In fact one of the deciding factors in choosing just when to make our Pluto flyby was the availability of Charon as a light source- we are flying past at a time when Charon lights Pluto's night side about as brightly as possible.

The trouble is that Charon's light is never very bright at all. In fact it's ridiculously faint- if you tried to walk around in Charon-light, you'd keep bumping into things. At the most, we expect Charon's light to be more than 10,000 times fainter than sunlight, and even sunlight, at Pluto's distance from the sun, is only about as bright as the tasteful lighting you might use in your living room in the evening. So to see those moonlit snowfields we need long exposures: 3 minutes is about the minimum that's useful. If we tried to take a single 3-minute exposure, though, two bad things would happen. First, the photo would suffer horrible camera-shake, because we can't hold the spacecraft steady enough for a sharp photo for more than half a second or so. Second, it would be completely overexposed, because the best time to look at the night side is when we are looking back at Pluto after our flyby, and at that time Pluto is only about 13 degrees from the Sun, less than the width of an outstretched hand. Sunlight will be flooding the inside of the camera, and everything we look at will be seen through a bright wash of background light. This stray light alone will be 1000 times brighter than Pluto's night side, and will overexpose the camera in a few seconds. We know just how bright the stray sunlight will be, because we've already taken test exposures on the spacecraft, in the same orientation. So instead of one 3-minute exposure we will take about 360 half-second exposures, which we will add together once they've been sent back to Earth. We will also need to take 360 exposures of blank sky, with the sun shining into the camera at exactly the same angle as for the Pluto images, so we can subtract away all that stray light.>>

[garyclaytonpalmer]

Apodman, You said "before we saw it from spacecraft", are you an astronaut?

[apodman]

Apodman, You said "before we saw it from spacecraft", are you an astronaut?

Only in my dreams. My spaceship controls were the knobs on my grandmother's dresser.

I meant "we" to mean the human race. The first photographic view of the far side of the moon was from the unmanned Soviet probe Luna 3 in 1959, and the first in-person view was during the U.S. Apollo 8 mission in 1968.

[garyclaytonpalmer]

So like me, you are actually a Astro"nut". I used to build Estes and Century Rockets when I was a kid in the 60's in NY. Built small versions of NASA rockets and shot them into the air...

[neufer]

There is no dark side of the moon really. Matter of fact it's all dark.

[Roy's wife does not believe how he got the burns on his face]
Roy Neary: Well they're not moon burns, goddamnit.
.......................................................
Project Leader: If we're all ready on the Dark Side of the Moon... play the five tones.

http://earthobservatory.nasa.gov/IOTD/view.php?id=38904

[bystander]

Cold hearted orb that rules the night,
Removes the colours from our sight,
Red is gray and yellow white,
But we decide which is right.
And which is an illusion?

[The Code]

Dark side of the moon,, pink floyd (amazing genius work) Wish you were here.

Mark

[neufer]

pink floyd (amazing genius work) Wish you were here.

In the Nirvana song, "Floyd the Barber", Kurt Cobain depicts a scene of Freudian
castration fears in which the whole town turns out to be a mass murderer.

Floyd the Barber is also referenced in the theme song for the TV series Freakazoid.