Starship Asterisk*

how coincidental is it that the moon just happens to be almost exactly the size of the disk of the sun to produce a total solar eclipse, or perhaps I should ask why? no where else that i assume, does this happen in the solar system, why or how is it that it only happems here?

Try this:

http://eclipse.gsfc.nasa.gov/SEsaros/SEsaros.html

It's not the exact link I was looking for, but it does have some good info. IIRC, the moon doesn't cover the sun fully during every eclipse. There are what are known as 'annular eclipses', which the sun looks like a thick-ish band or ring around the lunar disk. I've seen images of this, and you can search for 'annular eclipse' in your favorite search engine and probably come up with some great images, as well.

Good luck! 8)

JuanAustin wrote:how coincidental is it that the moon just happens to be almost exactly the size of the disk of the sun to produce a total solar eclipse, or perhaps I should ask why? no where else that i assume, does this happen in the solar system, why or how is it that it only happems here?

http://apod.nasa.gov/apod/ap080807.html

Old Sol's diameter is 400 times larger than Luna's and also 400 times further; there for the relative size seems the same from Earth. That's what causes the total eclipse. It is unusual that they happen to be that just exact same ratio. I believe there are total eclipses that occur on Jupiter; but the ratio is different.

Orin

Today's remarkable APODsomehow reminds me of a black hole... I can faintly make out the outline of a pony in the midst of the darkness.

JuanAustin wrote:how coincidental is it that the moon just happens to be almost exactly the size of the disk of the sun to produce a total solar eclipse, or perhaps I should ask why? ...

Why??? Perhaps it has something to do with engineering life support. Perhaps it's just a subtly of design. We each have to make our own decisions about what such things mean or represent… for me, it is an illustration of the subtly of design… I personally see the moon, earth, sun and universe as a wonderfully engineered and intricate, infinitely incredible work of Art. You may get a different answer from someone more in tune with planetology or astrophysics.

JuanAustin wrote:how coincidental is it that the moon just happens to be almost exactly the size of the disk of the sun to produce a total solar eclipse, or perhaps I should ask why? no where else that i assume, does this happen in the solar system, why or how is it that it only happems here?

Take any point of reference in space and measure the distance to the sun. Take the ratio of the diameter of the sun to this distance. Now take any object and place it between you and the sun. Now move that object away or towards you until that object just blocks out the sun. The ratio of that object's diameter to its distance from you will equal the ratio of the solar diameter to the solar distance obtained previously.

The smaller the object is, the closer it will have to be to you (or the further away the sun) to block the sun.

It is very coincidental that the angular size of the moon is the same as that of the sun, and that coincidence is not always true. The distance between the sun and earth varies, as does that between the earth and moon, so the ratios and angular size vary. That is why sometimes we have annular eclipses instead of total eclipses.

bystander wrote:... The distance between the sun and earth varies, as does that between the earth and moon, so the ratios and angular size vary. That is why sometimes we have annular eclipses instead of total eclipses.

Thought these links might add to the discussion...

http://antwrp.gsfc.nasa.gov/apod/ap070709.html

http://antwrp.gsfc.nasa.gov/apod/ap071025.html

http://www.windows.ucar.edu/tour/link=/ ... arth3.html

http://www.windows.ucar.edu/tour/link=/ ... l&edu=high

So is the moon lopsided or something?Because I can only see the "sun beads" off the sides of the moon.The actual sun doesn't even appear off the top and bottom of the moon.

Tidal effects result in an increase of the mean Earth-Moon distance of about 3.8 m per century, or 3.8 cm per year. [50] As a result of the conservation of ...

http://en.wikipedia.org/wiki/Moon

The moon was much more closer to earth a billion year ago wich must had made very long eclipse that must had made the earth day look like total night(uhh may not that much but more look like night).
In a billion year the moon will not hide the sun at all (Cause his distance to earth will have increase.). It will always be anular eclipse in those time. We happen to be at the right time in earth history to have the moon almost the same apparent size as the sun. Lucky us.

jesusfreak16 wrote:So is the moon lopsided or something? Because I can only see the "sun beads" off the sides of the moon. The actual sun doesn't even appear off the top and bottom of the moon.

Neither the sun, nor the moon are perfectly spherical, but today's apod explains the "sun beads".

... Bright beads around the Moon's dark silhouette are rays of sunlight shining through lunar valleys at the edge of the lunar disk. ...

jesusfreak16 wrote:So is the moon lopsided or something?Because I can only see the "sun beads" off the sides of the moon.The actual sun doesn't even appear off the top and bottom of the moon.

The image today is a composite of two different positions of the moon... one is leading just before totality and the other is trailing... two images in one.

What is most interesting to me is how the valleys of the moon give themselves away (sun beads) in the silhouette. And aren't the hot plasma structures cool... I mean HOT!!!

bystander wrote:Neither the sun, nor the moon are perfectly spherical, ...

Here is a tidbit on the Moon's shape...

http://space.newscientist.com/article/dn9670

Sun's shape...

http://en.wikipedia.org/wiki/Sun#structure

Just for grins... the Earth's shape...

http://en.wikipedia.org/wiki/Earth#shape

bystander wrote:

JuanAustin wrote:how coincidental is it that the moon just happens to be almost exactly the size of the disk of the sun to produce a total solar eclipse, or perhaps I should ask why? no where else that i assume, does this happen in the solar system, why or how is it that it only happems here?

Take any point of reference in space and measure the distance to the sun. Take the ratio of the diameter of the sun to this distance. Now take any object and place it between you and the sun. Now move that object away or towards you until that object just blocks out the sun. The ratio of that object's diameter to its distance from you will equal the ratio of the solar diameter to the solar distance obtained previously.

The smaller the object is, the closer it will have to be to you (or the further away the sun) to block the sun.

It is very coincidental that the angular size of the moon is the same as that of the sun, and that coincidence is not always true. The distance between the sun and earth varies, as does that between the earth and moon, so the ratios and angular size vary. That is why sometimes we have annular eclipses instead of total eclipses.

Well, the moon is moving away from us a few cm each year (apparently) and indeed it was once much closer. The tides and eclipses experienced by the dinosaurs would have been far greater than they are now. Many years from now we won't get any more total eclipses as the moon recedes to a point where it can no longer cover the sun and all we'll get are annular eclipses.
We should think ourselves lucky indeed that we just happen to be able to witness total eclipses now at a time in human evolution when there is so much information and knowledge available to be able to appreciate them for what they are. That's not just a good coincidence, it's incredibly fortuitous!

links discussing moon and earth gravitational relationship...

http://www.physlink.com/education/askexperts/ae695.cfm

http://www.gsfc.nasa.gov/scienceques2004/20050318.htm

http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html

"weebles wobble but they don't fall down"

From another thread: People Doin' Silly Things to the Moon (APOD 20080801)

neufer wrote:Phobos does a reasonable facsimile of a solar eclipse as seen from the surface of Mars:

http://en.wikipedia.org/wiki/Solar_eclipses_on_Mars

Does any other solar system moon do a better job of simulating a total eclipse as seen the surface of its mother planet?

Does any other solar system moon do a better job of simulating a total eclipse as seen the surface of a neighboring moon?

I would think Jupiter and Saturn systems would have a good chance (large moons and considerable distance from the sun). Neptune and Uranus also have substantial moons and even greater distance. Pluto/Charon would definitely be a good candidate, or maybe some asteroid pair in the asteroid belt. Eris is known to have a moon and the sun would seem quite small from there. And what about Ceres? Does it have any significant satellites?

Jovian and Saturnian moons do cast good eclipse shadows on the cloud tops of those gas giants, unfortunately there is no surface to stand on and view the totality event. Only Earth and Mars supply the necessary solid surface at a non crushing pressure with sufficiently transparent atmosphere and required moon for the eclipsing transit event.
There was an APOD on 06-10-16 that showed a great possible lunar eclipse viewpoint for Saturn.

I dont believe the Saturn total eclipse... the Sun would be too small at Saturn's distance for it to create that ring around the planet like the Sun does with the moon. Cool artist image though. But not likely.

The Cassini orbiter was 2.2m kilometers from Saturn when, over a period of 3 hours, some 27 panoramic images were taken and then stitched together to form that dramatic image of Saturn. Iapetus orbits Saturn at a distance of 3.5m kilometers so, If standing on Iapetus, you might view such an eclipse image.

I dont believe the Saturn total eclipse...

Just because it's hard to believe, doesn't make it any less authentic of an image. See here:

http://photojournal.jpl.nasa.gov/catalog/PIA08329

and here:

http://ciclops.org/view.php?id=2230

Extremely cool! 8)

So then the Sun is small, because it took 12 hours for the light to register as it looks in those combined exposures as Saturn eclipsed the sun for that long. So yeah, not really the same as it is on earth, but it looks cool. The moon only blocks out the sun for how long? =)-~

That's kind of what I was getting at.