Earth's Shadow (APOD 20 Aug 2008)

[orin stepanek]

http://apod.nasa.gov/apod/ap080820.html

What an interesting composite picture this is. It creates a nice silhouette of the earth. It also shows that even as the shadow cones down the further from the Earth; it is still quite large compared to the diameter of the moon.
Reminds me of the Gale Storm song [Dark Moon].

Orin

[emc]

Agreed! The image is very interesting... The longer I gazed I began to see the silhouette of a hairy head cast over a stack of moon pictures. Of course it's just my imagination...

Gale Storm huh... I remember watching My Little Margie, she gave her Dad a hard time!

[NoelC]

Wonderful image!

Many thanks to Anthony Ayiomamitis for illustrating so beautifully the size of the Earth's shadow at the distance of the moon. Having only seen it at any one time eclipsing a single moon I would have guessed that it would have been smaller relative to the size of the moon. This is a real eye opener!

-Noel

[henk21cm]

http://apod.nasa.gov/apod/ap080820.html
It also shows that even as the shadow cones down the further from the Earth

Look at the third moon from the left. The shadow cone does not 'fit' to the generally circular pattern. From Mare Humorum over Fra Mauro towards Sinus Medii the cone pattern seems to be too far to the west. It may be an optical illusion, caused by the darker shade of gray of the Mares. For a similar effect in the third moon from the right the selenographical location of Mare Fecunditatis and Mare Nectaris is too far to the east compared to Mare Humorum for a comparison.

Note that another optical illusion can be seen. When looking at the north of all moons, is looks like the line is concave: the north of darkest moon looks to be a little too far to the bottom left corner. It's an optical illusion, since when you align the norths of all moons with a sheet of paper, the darkest (central) moon is even a little too far to the top right corner, the opposite of what you think that you are seeing!

Although Mare Humorum hasn't got anything to do with humor, Ed emc's idea isn't utterly lacking humor: to fake a lunar eclipse with the head of a bold man. In Eds view boldness still has a purpose in astronomy.

[orin stepanek]

Hmm! I wonder why the shadow isn't crisp on the moon. Is it because of the Earth's atmosphere causing some distortion, or maybe the motion of the moon passing through it?

Orin

[emc]

hair stubble

[BMAONE23]

Many millions of years ago the moon appeared to be the same relative size as the earths shadow though I don't think there was any creature alive to appreciate the possibility of a Lunar annular eclipse.

[orin stepanek]

hair stubble

I would say Henry's head; but, Henry was bald.
Maybe someone forgot to mow their lawn.

Orin

[orin stepanek]

Many millions of years ago the moon appeared to be the same relative size as the earths shadow though I don't think there was any creature alive to appreciate the possibility of a Lunar annular eclipse.

I thought the moon was gradually getting farther from the Earth.

http://www.irishscientist.ie/2000/conte ... sight3.xsl

Orin

[bystander]

I thought the moon was gradually getting farther from the Earth.

Yes, and as it recedes its apparent size gets smaller. Conversely, millions of years ago, it must have been immense, maybe even larger than the earth's shadow.

[emc]

I think BMAONE23 is indicating to us that the moon was closer to earth in ions past more closely matching the size of the earth's shadow.

What is so cool to me is how we humans are in such a good position relative to the moon, earth, sun, and galaxy. We are "out on a limb" so to speak from the Milky Way center, providing a good cosmic vantage point for observation. We are at a survivable position relative to the sun, although it sure was hot yesterday! We have a good relationship with the moon for promoting life as well... kinda makes me want to howl! It's like we are born into a cosmic window of opportunity amid a beautifully and intricately designed set of celestial objects... spun up for us (Big Bang?) now winding down as the moon recedes and the earth slows down. What an incredible balance we live in! Or am I missing something?

[neufer]

I thought the moon was gradually getting farther from the Earth.

Yes, and as it recedes its apparent size gets smaller. Conversely, millions of years ago, it must have been immense, maybe even larger than the earth's shadow.

It would have to be larger than the earth then!

If it ever gets to 1M miles away, however, the earth's umbra will be just a small dot on the moon. Before that the umbra will be the size of the moon.

[neufer]

Hmm! I wonder why the shadow isn't crisp on the moon. Is it because of the Earth's atmosphere causing some distortion...?

That's part of it but mostly the gray penumbra is the width of the moon itself.

[neufer]

Gale Storm huh... I remember watching My Little Margie, she gave her Dad a hard time!

Well that dates all of us. Gddddddddddddddd....
(Where's Mrs. Odetts when you need her?)

http://www.sitcomsonline.com/sounds/mylittlemargie.wav

[emc]

Orin went out on a limb and I couldn't leave him hanging by himself

[orin stepanek]

Orin went out on a limb and I couldn't leave him hanging by himself

Thanks Ed; I think!
I used to watch "My Little Margie." That was back in the back and white days. I think one of our neighbors had a color set back in the 50's; but I don't think "My Little Margie" was in color. Of course I wouldn't know as we had a black and white. I used to listen to music as a teen. "Dark moon" was a favorite of mine back then. Now I"m telling on my age. 

Orin

[BMAONE23]

I thought the moon was gradually getting farther from the Earth.

Yes, and as it recedes its apparent size gets smaller. Conversely, millions of years ago, it must have been immense, maybe even larger than the earth's shadow.

It would have to be larger than the earth then!

If it ever gets to 1M miles away, however, the earth's umbra will be just a small dot on the moon. Before that the umbra will be the size of the moon.

Neufer,
I sit corrected. The Moon would in deed need to be larger to have the proposed annular eclipse. As it was closer to the Earth in the past, it was also closer to the larger portion of the earths shadow so while the moon would appear larger in the sky, the shadow play would also take place in a closer and therefore larger portion of the earths shadow.

[emc]

Orin went out on a limb and I couldn't leave him hanging by himself

Thanks Ed; I think!
I used to watch "My Little Margie." That was back in the back and white days. I think one of our neighbors had a color set back in the 50's; but I don't think "My Little Margie" was in color. Of course I wouldn't know as we had a black and white. I used to listen to music as a teen. "Dark moon" was a favorite of mine back then. Now I"m telling on my age. 

Don't worry Orin, your only old if you think you're old... I had a black and white Silvertone in my bedroom. It would only work if you slapped the side of the cabinet. I think the TV was born the same year as me, 1951. Also the same year the movie The Day the Earth Stood Still came out, although I don't believe there is any significance in my birth.



Klaatu barada nikto

[orin stepanek]

It's amazing that Luna is receding at 3.8cm/year and that that can be measured.

http://www.talkorigins.org/indexcc/CE/CE110.html

Some future time the moon will pass through the conical shadow and it will be = to the moon's diameter. The moon will be quite a bit smaller in the sky I recon.

Orin

[orin stepanek]

Orin went out on a limb and I couldn't leave him hanging by himself

Thanks Ed; I think!
I used to watch "My Little Margie." That was back in the back and white days. I think one of our neighbors had a color set back in the 50's; but I don't think "My Little Margie" was in color. Of course I wouldn't know as we had a black and white. I used to listen to music as a teen. "Dark moon" was a favorite of mine back then. Now I"m telling on my age. 

Don't worry Orin, your only old if you think you're old... I had a black and white Silvertone in my bedroom. It would only work if you slapped the side of the cabinet. I think the TV was born the same year as me, 1951. Also the same year the movie The Day the Earth Stood Still came out, although I don't believe there is any significance in my birth.



Klaatu barada nikto

We all have some effect on someones life somehow or another; so I guess we are all hare for some reason. I guess I'm 11 years your elder. I hope you got to watch that movie.

Orin

[henk21cm]

Yes, and as it recedes its apparent size gets smaller. Conversely, millions of years ago, it must have been immense, maybe even larger than the earth's shadow.

I do not think so. When you approach the earth, from the current postion of the moon, the part of the sky blinded by the earth, increases in size. Although the size of the moon will increase as well, it can always hide itself in the earth's shadow, since the moon is considerably smaller than the earth.

More interestingly is the distance between moon and earth when there is just one location on the moon where a solar eclipse can be seen. Since the earth is about 3.5 times larger than the moon, this distance is about 1.5 E6 km. Currently (and in the past) a full solar eclipse on the moon is not localized within an narrow band as on earth, but extends to an entire hemisphere.

• Note 1 that the other hemisphere of the moon (the dark side of the moon according to Pink Floyd) will never experience a solar eclipse.
  Note 2 that last saturdays lunar eclipse was just a partial eclipse and observers far in the north of the moon would not have seen a full solar eclipse.

More to read on the distance between earth and moon, see e.g.:

http://www.astro.uu.nl/~strous/AA/en/an ... ijden.html

http://www.aerospaceweb.org/question/as ... 0262.shtml

[emc]

... [snipped]
We all have some effect on someones life somehow or another; so I guess we are all hare for some reason. I guess I'm 11 years your elder. I hope you got to watch that movie.

I did see the movie and liked it very much. I thought the robot's laser eye was super cool.

[emc]

...[snipped]More interestingly is the distance between moon and earth when there is just one location on the moon where a solar eclipse can be seen. Since the earth is about 3.5 times larger than the moon, this distance is about 1.5 E6 km. Currently (and in the past) a full solar eclipse on the moon is not localized within an narrow band as on earth, but extends to an entire hemisphere.

• Note 1 that the other hemisphere of the moon (the dark side of the moon according to Pink Floyd) will never experience a solar eclipse.
  Note 2 that last saturdays lunar eclipse was just a partial eclipse and observers far in the north of the moon would not have seen a full solar eclipse.

More to read on the distance between earth and moon, see e.g.:

http://www.astro.uu.nl/~strous/AA/en/an ... ijden.html

http://www.aerospaceweb.org/question/as ... 0262.shtml

Hi Henk,

It could be cool if someone would create a 3D model solar system that allows position distortion (move objects closer together than normal) to illustrate the orbital relationships. I think I understand the moon's orbit now but I am not 100% confident.

I'm wondering about the illustration of the moon's orbit at the aerospaceweb site... Isn't the illustration from http://www.aerospaceweb.org/question/as ... 0262.shtml a bit off? It shows the moon's orbit inclined about 30 degrees



When it is actually 5.14 degrees...


schematic illustration from http://en.wikipedia.org/wiki/Moon

[BMAONE23]

... [snipped]
We all have some effect on someones life somehow or another; so I guess we are all hare for some reason. I guess I'm 11 years your elder. I hope you got to watch that movie.

I did see the movie and liked it very much. I thought the robot's laser eye was super cool.

I hope the remake does justice to the original. Keanu Reeves seems like a pretty good casting move for the part of Klaatu though

[emc]

Hi BMAONE23,

I hope to see the remake as well. I expect the special effects will certainly outshine the original and I would like to see the condition of shutting down the earth's technology explained... at least a little. Give us some meat to chew on I say. We are not the easy SciFi prey we were in 1951.