Why do we not observe solar and lunar eclipse every month?
Question:
Answer:
ummm ... why should we??
Because lunar and solar eclipses don't happen every month. These events are rare. Each event is when the sun is blocking the moon and vice versa. This is not a new moon and a full moon, contrary to popular belief.
Their orbit cross each other forming an 5 degrees angle; for that reason not each new or full moon result a sun/moon eclipse :)
The distance to the moon and the fact that the moon's orbit varies a bit. When you have a solar eclipse only the very thin shadow of the moon draws across the sunlit part of earth. The odds of the shadow hitting a well populated town is pretty small. The shadow does however fall in space every day.
On a lunar eclipse the moon passes through the earth's shadow and this shadow is much bigger, but still pretty rare. The earth is after all tilting in comparison to the plane of the moon and the sun, so the chances aren't that big.
The natural question is why doesn’t every new moon bring a solar eclipse? The moon’s orbit is tilted with respect to the ecliptic by 5 degrees so that at most new moons the moon’s shadow passes above or below the Earth. However, because of this tilt, the moon must pass through the ecliptic plane about twice a year. The point where the lunar orbit passes through the ecliptic is called a node and the line connecting the two nodes is called the line of nodes. If the moon is near a node during new moon, a solar eclipse will occur. The moon is close enough to a node for its shadow to fall on the Earth for about 38days. This interval is called the eclipse season. Since the synodic lunar month, 29.5 days, is shorter than an eclipse season, a solar eclipse must occur during each eclipse season. In fact, if an eclipse occurs just at the beginning of the eclipse season, a second eclipse will occur at the end. In this case, both eclipses will probably be partial, the central part of the shadow (umbra) missing the Earth above and below each pole. In general, the eclipse is a total eclipse only about a third of the time; more often it is a partial or annular eclipse.
The above information is also why we do not see lunar eclipses every month.
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