10 replies to this topic

[benw]

I'm just watching a program on Discovery about solar eclipses and it made me think. How amazing is it that, when viewed from the surface of the earth, the moon is the perfect distance away for it to appear to be exactly the same size as the sun? I mean, what are the chances of that? The creation of the solar system must have been incredibly random but somehow the sun, earth and moon turned out to be exactly the right size, shape and distance apart to create a perfec eclipse. I'm not normally in to all that space exploration thang but I never really thought of this before and now I'm fascinated!

Edited by benw, 26 November 2004 - 09:12 PM.

[paulb]

Seeing a solar eclipse is one of the most amazing things I have ever done. I saw the 2001 one from the banks of the Kafue river in Zambia, not a cloud in the sky. It was truly amazing. Already planning for 2006. The most amazing thing for me was the 'diamond ring' where the suns rays are defracted by the edges of the mountains on the moon for the last few seconds before totality.

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[paulb]

And then the corona is visible during totality. The thing I'd not thought about before was that in the middle of totality, there was a glow all around. It was like dawn for 360 degrees. Truly awesome.

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[jules_s]

quite obvious really....all planets/satellites (moons) are on an eliptical orbit around each other.... hence the orbits and distances only align once in a while to give the optical percepton that the planets/moons are the same size

[paulb]

Bollox We are in a slightly eliptical orbit around the sun and the moon is in a slightly eliptical orbit around us. The orbits are slightly inclined which means and eclipse doesn't happen very often. The amazing thing is that the moon and sun both subtend half a degree of arc, which means when the orbits are right, the moon can cover the sun but not the corona. This is entirely a co-incidence. By your reckoning, the transit of Venus earlier this year could result in the Sun being completely obscured rather than a dot being seen. The Earth and it's Moon are the only planet/moon combination in the solar system where the moon and the sun are perceived to be the same size when viewed from the surface of the planet.

[jneill]

Bollox

[jules_s]

Bollox

So why does some days the moon look absolutely mahoosive and other a helluva lot smaller?

[benw]

Bollox

So why does some days the moon look absolutely mahoosive and other a helluva lot smaller?

Well, there's no argument about whether the orbits are eliptical or not. That's fact (We wouldn't have tides if they weren't). But the orbits are not exactly parallel with each other, the moon, sun and earth have to be exactly the right distance away from each other and the moon and sun have to be exactly the right size for it to work. Of all the infinate combinations of size, distance and orbit that could have been created it just so happened that it came out perfectly. One small variation either way would have made eclipses impossible. Isn't that amazing?

Edited by benw, 28 November 2004 - 10:12 AM.

[paulb]

Bollox

So why does some days the moon look absolutely mahoosive and other a helluva lot smaller?

I dunno. It doesn't to me. The moon varies it's orbit by +/- 6% which means that when viewed from the surface of the earth it varies in angle subtended between 0.512 degrees at apogee to 0.584 degrees at perigee.

If you are saying that 0.072 degrees is the difference between "mahoosive" and not then you have better eyes than me.

[jules_s]

look here then...

>clicky<

[paulb]

Yep, that page agrees with me...

The Moon's orbit is ECCENTRIC by 0.0549.

This means the Earth-Moon distance varies up and down from the mean Earth-Moon distance by about 5.5 %. The total range of variation is 11 %.

The 11 % variation in DISTANCE causes Moon's ANGULAR SIZE ON THE SKY vary by 11 % too.

The variation in angular size is probably too small ever to be noticed by casual observation since we usually see the Moon at perigee and apogee without a convenient STANDARD OF COMPARISON.

I said +/- 6%, they said 11% which is the same thing, allowing for rounding errors.

So you are saying that variation in angular size is probably too small ever to be noticed by casual observation

backs up your claim that

the moon look absolutely mahoosive and other a helluva lot smaller

Obviously your eyesight really is that good.