Eclipse Interactive (110.0K)

1		Which of these statements about the geometry of eclipses is FALSE?
			A)	A solar eclipse must happen at new moon.
			B)	A lunar eclipse happens every full moon.
			C)	Total solar eclipses must happen near perigee.
			D)	The Earth's umbra covers the full moon, but the moon's umbra only a tiny portion of Earth.

In history, we have learned much about the Sun, Moon, and Earth from careful observation of them. In fact, perhaps the first use of the scientific method dates back to Aristotle's observations of lunar eclipses.

2		What two profound observations did Aristotle make concerning Earth and Moon from his many observations of lunar eclipses during his long life? Need a Hint?
			A)	The Earth must be revolving around the sun, because it is smaller than the Sun.
			B)	The shadow of the Earth on the Moon is black, for the solid Earth blocks all sunlight from reaching the eclipsed moon.
			C)	The Earth is a sphere about four times larger than the moon.
			D)	The Moon must be orbiting exactly in the ecliptic plane, or there would be no eclipses.

Lets look at how eclipses have enriched our knowledge as well as thrilled our senses, especially total solar eclipses, such as coming to the United States on August 21, 2017.

3		If you are in Charleston, South Carolina, on August 21, 2017, about 2:50 PM in the afternoon, what three special conditions exist to allow you to see totality? Need a Hint?
			A)	We have a new moon, on the ecliptic, and near perigee.
			B)	We have a full moon, at a node, and near perigee.
			C)	We have a new moon at apogee.
			D)	We have a new moon, at a node, and near apogee.

Eclipses are rare events, because the geometry you explored in this interactive must be just right. Lets compare the two types of solar eclipses, for instance.

4		At perigee, the moon is big enought to cover the Sun and produce totality. At apogee, we instead see a ring of fire left over in an annular eclipse. But in April 2005, we had a "hybrid eclipse", which was both annular and total. How could this be? Need a Hint?
			A)	The Moon moves fast enough in orbit at at the start of the eclipse, it was too distant to cover the Sun, but by eclipse end, was close enough to give a brief totality.
			B)	The Sun pulsates, and at its largest, is briefly larger than the disk of the Moon.
			C)	The Earth's orbital motion brings us close enough to the Sun during the eclipse that the Sun grows large enough to give us an annular eclipse by the end of the day.
			D)	The Earth has a 4,000 mile radius, so at dawn and dusk, the moon is too small and distant to cover the Sun, but near noon, we are now close enough to the Moon that a few seconds of totality can occur.

Let's use the geometry again, to explore the duration of a total solar eclipse under the best of conditions.

5		Given that the moon's umbral shadow is about 100 miles across, and that the moon's orbital motion causes this shadow to sweep from west to east across the Earth at about 1,000 mph, how long can this totality last, if you are in the center of the path? Need a Hint?
			A)	About 1.5 hours
			B)	About three hours.
			C)	About six minutes.
			D)	About three minutes.