by Anthony Barreiro » Mon Nov 04, 2013 9:22 pm
MarkBour wrote:Beyond wrote:On average:
- 1) I have cloud filled skies whenever an astronomical event occurs.
2) I spend a lot of time with my head below the clouds.
Hear, hear. It seems to happen to me a lot, too. I'm hoping ISON will be good and that I won't have party-spoiling weather.
----------
I can understand that the angular size of the Moon from Earth's surface is nearly the same as the angular size of the Sun. It seems like an amazing coincidence, but there it is. And I'm guessing that when the Moon is farther away from the Earth during an eclipse, we get an annular eclipse, and when closer, to us, we get a full eclipse. For a hybrid eclipse, then, I guess it has to be at just about the right distance for a minimal full eclipse, and is it correct that lower elevations on the Earth would see the annular eclipse, while higher elevations would get the full eclipse, by being a little closer to the Moon? (They're also closer to the Sun, but the relative distance change to the Moon would be much greater than to the Sun.) And it's a matter of "true elevation" from the center of the Earth, rather than elevation above sea level, which is a bit irregular.
As a rank amateur, I believe I can figure this out, but I'm really just asking if I have this correct ...
My understanding is that the Earth's total size is a much more significant factor in causing hybrid annular-total eclipses than are variations in elevation. The highest points on Earth are less than 10 km above sea level. With a diameter of about 13,000 km, the surface of the Earth at the noontime meridian is about 6,000 km closer to the Sun than the surface of the Earth at the sunrise and sunset meridians.
Solar eclipses happen at new Moon, when the Moon is between the Earth and the Sun in space. The surface of the Earth at the sunrise meridian is farther from the Moon than the surface of the Earth at the noontime meridian. So as the Moon orbits the Earth her umbral shadow is not quite long enough to reach the surface of the Earth at sunrise, but as she orbits toward the Earth's noon meridian there is less distance between the surface of the Earth and the Moon, so the Moon's umbra is just long enough to reach the surface of the Earth. Voila.
[quote="MarkBour"][quote="Beyond"]On average:
[list]1) I have cloud filled skies whenever an astronomical event occurs.
2) I spend a lot of time with my head [u]below[/u] the clouds.[/list][/quote]
Hear, hear. It seems to happen to me a lot, too. I'm hoping ISON will be good and that I won't have party-spoiling weather.
----------
I can understand that the angular size of the Moon from Earth's surface is nearly the same as the angular size of the Sun. It seems like an amazing coincidence, but there it is. And I'm guessing that when the Moon is farther away from the Earth during an eclipse, we get an annular eclipse, and when closer, to us, we get a full eclipse. For a hybrid eclipse, then, I guess it has to be at just about the right distance for a minimal full eclipse, and is it correct that lower elevations on the Earth would see the annular eclipse, while higher elevations would get the full eclipse, by being a little closer to the Moon? (They're also closer to the Sun, but the relative distance change to the Moon would be much greater than to the Sun.) And it's a matter of "true elevation" from the center of the Earth, rather than elevation above sea level, which is a bit irregular.
As a rank amateur, I believe I can figure this out, but I'm really just asking if I have this correct ...[/quote]
My understanding is that the Earth's total size is a much more significant factor in causing hybrid annular-total eclipses than are variations in elevation. The highest points on Earth are less than 10 km above sea level. With a diameter of about 13,000 km, the surface of the Earth at the noontime meridian is about 6,000 km closer to the Sun than the surface of the Earth at the sunrise and sunset meridians.
Solar eclipses happen at new Moon, when the Moon is between the Earth and the Sun in space. The surface of the Earth at the sunrise meridian is farther from the Moon than the surface of the Earth at the noontime meridian. So as the Moon orbits the Earth her umbral shadow is not quite long enough to reach the surface of the Earth at sunrise, but as she orbits toward the Earth's noon meridian there is less distance between the surface of the Earth and the Moon, so the Moon's umbra is just long enough to reach the surface of the Earth. Voila.