Solar Eclipse

Overlord

Hello all. Ive been wondering about this one for a while!
During a total eclipse of the sun, the moon is a perfect fit to mask the solar disk and allows us to see the suns corona. Is this a cosmic fluke? The moon just happens to be the right size/distance between earth and the sun so that it perfectly covers the solar disc ? or is there a simpler explanation?

Sir Digby Chicken Caesar

God.

Dampsquid

Yes, its just a coincidence that they appear roughly the same size in the sky!

Sev

Coincidence I guess. Another thing to note is that the moon's rotational period is exactly the same as its orbital period, such that it the same side always faces earth. That's not coincidence tho, but im not sure of the physics behind it.

Saruman

Not exactly Sev... but its very close!! Nothing in Astronomy is exact... its all an educated Guess. It seems we see the same face of the moon but its not exact... we might see a little more of one side than the other at certain times but unless you know the face of the moon better than the palm of your hand (and most people dont even know that) then you will just think its the same as always. Just like the earth is not spinning on its axis in perfect rotation.. there is a slight wobble... Just like the Equator of the sun spins faster than the poles etc... no one knows why but nothing is exact. The earth is not a perfect sphere, Jupiter is definatly not.. its all squished etc.

Oh and on topic.. yes its a coincidence thats all. And its only the same size in apparent viewing on the path of totallity.... anywhere else it does not cover the whole sun. Its a very small coincidence at that.

Sev

That phenomenon is called lunar libration, and it is not a result of there being a difference in the orbital and rotational periods of the moon. It is in fact mostly attributed to the eccentricity (ellipticity) of the moons orbit. The fact that it is closer to the earth at specific points in its orbit, it in effect, speeds up such to move that extra distance in its orbit before its rotation can catch up. This allows us to glimpse thin slivers of the moon's edges at times that we can not normally see as you said. But the orbital and rotation period are essentially identical (obviously not exactly, nothing can be) but, perhaps off by microseconds maybe such that in a few thousand or million years we would be generally facing a slightly different side of the moon, but thats well outside our lifetimes, and for the sake of argument.. negligible.

Gordon

When is the next lunar/solar eclipse btw?

Sev

Also, the apparent size of the moon is not always large enough to cover the apparent size of the sun, so sometimes we have what are known as 'annular eclipses'. You do not experience totality (darkness) as such, but mid-eclipse, the sun appears as a ring so the corona is not visible as with a total eclipse. Depending on the position of the moon in its orbit at the time of eclipse you can have total eclipses of different lengths, ranging from like 30 seconds to 10 minutes of darkness. It's an odd sensation once it goes total, its daylight bright up until the very last bead of sunlight is extinguished, then, almost as like somebody just quickly turned a dimmer switch, it goes twilight dark. On the whole tho.. the moon and sun are pretty much the same apparent size, its convenient.

Sev

http://sunearth.gsfc.nasa.gov/eclipse/solar.html

The next total solar eclipse is in November, and will be seen partially eclipsed from south america and australia, but for totality you'll have to trek to Antarctica

The next total lunar eclipse is in november too.

Capt'n Midnight

No other REAL planet has a moon so large compared to it's self.
The moon is slowly drifting away (~2cm per year?) and is slowing the earths rotation (tides). There used to be 400 days in a year -- the moon is locked in to the earth because it's day slowed down faster. Our day will slow down too until only one side of the earth will see the moon. Then the moon will start drifting in again - all the way in....

So the fact that the apparent size of the sun and moon are the same when seen from earth are coincidence in size, orbital mechinics and time - in the distant past eclipese were more total -no annular's and in the future there won't be full eclipses for a long time...

And of course one day the sun will be a red giant... and our galaxy will collide with Andronomada (SP)

Note: the moonwobblesa bit and you can use parallex to see different parts of it from different parts of the earth - so ~57% of it visible not just 50%.

Jaffus

Well a few million years ago the moon would have totally covered the sun during an eclipse, now it is just the same size and in an other few million years it will be just just a dot on the face of the sun.....

Capt'n Midnight

it was a lot more than a "few" million years ago that the moon would cover the sun when at worst case orbital positions (moon far - sun close)

If the earth was not tilted on it's axis then we'd monthly solar and lunar eclipses.

The duration and totallity and frequency of lunar eclipses is cos the distance between bodies is similar to solar eclipses but the ratios of size are quite different.

Hmmm - somewhere out there there is a rocky planet with a moon made from ICE or Lithium - it would get lots more eclipses ...

Jaffus

Im sure there is alot of stuff you know about but Im damn sure there is a lot of thing I know more about than you and the point of posting is to learn and be corrected not a competion to see who is the most intelligent.

Capt'n Midnight

the point of posting is to learn and be corrected

halenger

Am I remembering correctly that the next Total Eclipse visible from Ireland is 2099 and that's only visible from Kerry?

I think that's right but I'm not sure.

Redshift

I used to have a link to a site which allowed you to calculate the next solar eclipse in your area, I'll try to find it again but from what I remember the next one in Ireland was a long long time away.

Ryan

Saruman

I dont know when it is in Ireland but i thought i heard it would happen in my lifetime again.. just many decades away (hope thats my lifetime ) Eh i have a list of some in a book at home.. might take a look

halenger

As far as I know 2099 is correct and also I think I remember the next one visible from Dublin being around 2300 something...

That is if Dublin is still there by then!!

Redshift

Yep it's a long way off well long enough away that none of us will see it. Has anybody here ever travelled to see a solar eclipse I would imagine a fair few form Ireland travelled to Cornwall but has anybody travelled further. I myself have never seen totality for myself:( But maybe someday. So who are the obsessed ones?

Red

albertw

Originally posted by Redshift
Has anybody here ever travelled to see a solar eclipse I would imagine a fair few form Ireland travelled to Cornwall but has anybody travelled further.

Yea, I was in Cornwall to watch some very dark clouds, confused and very quiet animals, and a depressed looking Patrick Moore on a portable telly. Couldnt afford to go any further on that occasion.

A fair few of the IAS/IAA/SDAS/etc. folks wander across the world chasing these shadows, some images at http://www.esatclear.ie/~ias/eclipse.htm

Cheers,
~Al

Sev

Originally posted by Redshift
Has anybody here ever travelled to see a solar eclipse I would imagine a fair few form Ireland travelled to Cornwall but has anybody travelled further.

I went to Varna, Bulgaria for the 1999 one. Beautiful, perfect, clear blue skies for two weeks.

cobyrne

Originally posted by Redshift
Has anybody here ever travelled to see a solar eclipse I would imagine a fair few form Ireland travelled to Cornwall but has anybody travelled further.

Check out http://www.ecliptomaniacs.com/ - the web site of a bunch of Irish eclipse chasers, who have been to Bulgaria, Madagascar, South Africa and Scotland.

DC NIEN

The next Solar eclipse visible in Ireland is a partial eclipse on 3/10/2005.......not that far off.
Whereas the next total solar eclipse visible is on 23/9/2090 and will be visible in Southern Kerry and South West Cork but it will probably be cloudy on the day which is why we travel to sunny climates to see them! See COBYRNE posting and www.ecliptomaniacs.com
The next Total Solar visible in Europe is from Southern Turkey on 29/3/2006
All those interested in astronomy should make an effort to see this one. They really are spectacular events which no photographs ever justify.