View Full Version : Something to Ponder

2009-Feb-05, 03:34 PM
Admitidly, I'm literally a beginner with this whole Astronomy stuff; but I have always found it interesting...at least the parts of Astronomy that I know (which again, itsn' much). One thing that I am a big fan of is travelling, and my question is this....on July 22, 2009 (or so they say) there will be an eclipse lasting a full 6 minutes. I get travel literature all the time and found that someplace out in China or something like that will have the best vantage point to witness this. Its a cruise; and if your interested you can view it all here.

My question is, can you really see the eclipse better from another part of the world? Again, excuse my ignorance, but it just doesn't make much sense to me.

2009-Feb-05, 05:38 PM
I think your confusion is in comparing a solar eclipse to a lunar eclipse. In a lunar eclipse you are looking at the shadow of the Earth on the Moon. But in a solar eclipse, you are not looking at the Moon's shadow on the sun.

A lunar eclipse -- where the Earth's shadow falls on the Moon -- can be seen from anywhere that the Moon can be seen. A solar eclipse is where the Moon's shadow falls on the Earth. This shadow is a relatively small spot which moves across the surface of the Earth. You will not see it unless you are in it's path and the shadow travels over you.

For example, here is the path of one particular solar eclipse (the path of the Moon's shadow over the surface of the Earth). Only those in that path see the eclipse.

2009-Feb-06, 02:09 PM
...For example, here is the path of one particular solar eclipse (the path of the Moon's shadow over the surface of the Earth).
(that lookes like the one of Mar 29, 06)

To reinforce some of that, I searched for some pictures I remember and found similar ones that you may want to peruse.

This is the map (http://eclipse.gsfc.nasa.gov/SEatlas/SEatlas3/SEatlas2001.GIF) of 2 decades (2001-2020) worth of eclipses. It's from the NASA Eclipse web site (http://eclipse.gsfc.nasa.gov/eclipse.html) with a lot of information. Right now the main page is showing a similar picture to centsworth's one, but for the upcoming eclipse.

Another interesting one is an actual view from space. This ISS/NASA page (http://science.nasa.gov/headlines/y2002/02dec_isseclipse.htm) is a press release from before the dec02 eclipse. It contains some information as to the one seen from Mir in 99 including a still of the actual view from space (also seen on APOD). It also has a good animated GIF which illustrates the difference between the penumbra (partial shadow) and the umbra (total shadow).

2009-Feb-07, 07:08 AM
Just as a simple explanation, remember that the moon is smaller than both the sun and the earth. So there is no way that the moon can cast a shadow from the sun over the whole earth. In fact, because the moon is smaller than the sun, the shadow is like a cone that gets smaller at it gets further away from the moon. So if the earth and moon were touching, the shadow would be about the size of the moon. But since there is a distance, the shadow is smaller than the moon.

I suppose you could imagine it like this. Take a basketball (the earth) and try to make it all dark (shield it from the sun) by putting a tennis ball (the moon) in front of it.