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Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.14.4 What was the origin of the Moon? Next Document: E.16 What's the Oort Cloud and Kuiper Belt? See reader questions & answers on this topic! - Help others by sharing your knowledge Author: Joseph Lazio <jlazio@patriot.net> A solar eclipse occurs when the Moon passes between the Earth and Sun and the Moon's shadow crosses the Earth, viz. (not to scale!) Sun Moon Earth Solar eclipses can be total, partial, or annular. A total eclipse is when the Moon obscures the Sun entirely. A partial eclipse is when the Moon only covers a portion of the Sun. Because the Moon's orbit about the Earth is not perfectly circular, sometimes it is slightly farther away from the Earth. If a solar eclipse occurs when the Moon is at the far point in its orbit, the Moon will not cover the Sun entirely. A thin ring, or annulus, of sunlight will be visible around the Moon. This kind of eclipse is called an annular eclipse. **Solar eclipses can be damaging to one's eyesight, unless proper precautions are taken!** See FAQ Question B.11 and the Eclipse Home Page, <URL:http://sunearth.gsfc.nasa.gov/eclipse/>. A lunar eclipse occurs when the Earth passes between the Moon and Sun, viz. (again, not to scale) Sun Earth Moon Lunar eclipses are either total or partial, depending upon whether the Moon moves completely into the Earth's shadow or not. Lunar eclipses are always safe to view. Eclipses do not happen once a month because the Earth's orbit about the Sun and the Moon's orbit about the Earth are not in the same plane. The above "pictures" are if one is looking "down" on the Earth from the North Pole (or "up" on the South Pole). If we look at the system from the side (looking at the Earth's equator), the typical situation is Sun Earth Moon (with the angle shown exaggerated greatly, the actual angle is about 5 degrees). Only when the three bodies are in the same plane can an eclipse occur. The total number of eclipses, both lunar and solar, never exceeds seven in a year. Because the Moon is so much smaller than the Earth, and casts a smaller shadow, solar eclipses are more infrequent than lunar eclipses; in a year, between 2 to 4 lunar eclipses will occur and at least 2 solar eclipses will occur. *Total* solar eclipses happen only every 1.5 years or so. For additional information see the Eclipse Home Page, <URL:http://sunearth.gsfc.nasa.gov/eclipse/>. User Contributions:Comment about this article, ask questions, or add new information about this topic:Top Document: [sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9) Previous Document: E.14.4 What was the origin of the Moon? Next Document: E.16 What's the Oort Cloud and Kuiper Belt? Part0 - Part1 - Part2 - Part3 - Part4 - Part5 - Part6 - Part7 - Part8 - Single Page [ Usenet FAQs | Web FAQs | Documents | RFC Index ] Send corrections/additions to the FAQ Maintainer: jlazio@patriot.net
Last Update March 27 2014 @ 02:11 PM
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[sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9)
Section - E.15 What's the difference between a solar and lunar eclipse? Where can I find more information about eclipses?
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[sci.astro] Solar System (Astronomy Frequently Asked Questions) (5/9)
Section - E.15 What's the difference between a solar and lunar eclipse? Where can I find more information about eclipses?
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with stars, then every direction you looked would eventually end on
the surface of a star, and the whole sky would be as bright as the
surface of the Sun.
Why would anyone assume this? Certainly, we have directions where we look that are dark because something that does not emit light (is not a star) is between us and the light. A close example is in our own solar system. When we look at the Sun (a star) during a solar eclipse the Moon blocks the light. When we look at the inner planets of our solar system (Mercury and Venus) as they pass between us and the Sun, do we not get the same effect, i.e. in the direction of the planet we see no light from the Sun? Those planets simply look like dark spots on the Sun.
Olbers' paradox seems to assume that only stars exist in the universe, but what about the planets? Aren't there more planets than stars, thus more obstructions to light than sources of light?
What may be more interesting is why can we see certain stars seemingly continuously. Are there no planets or other obstructions between them and us? Or is the twinkle in stars just caused by the movement of obstructions across the path of light between the stars and us? I was always told the twinkle defines a star while the steady light reflected by our planets defines a planet. Is that because the planets of our solar system don't have the obstructions between Earth and them to cause a twinkle effect?
9-14-2024 KP