UCSB Science Line
 Why are some solar eclipses longer than others? Question Date: 2017-08-25 Answer 1: The duration of an eclipse depends on several factors. First, it depends whether it is a partial or total eclipse. Then it depends on how close the moon is to Earth in its elliptical orbit (affecting the apparent size and speed of the moon). And lastly, it depends on how close Earth is to the sun in its orbit (affecting the apparent size of the sun). On average a total eclipse lasts a couple hours from start to finish, with totality (when the sun is completely obscured) lasting only a couple minutes. Answer 2: The moon's orbit isn't perfectly circular. When the moon is closer to the earth, it appears larger in the sky, and when the moon is farther away, it appears smaller. If the moon is close to the earth, then the size of the shadow that it casts on the earth is bigger, and so takes longer for the moon to move out of the way in its orbit. The opposite happens if the moon is farther away, and if it is really far away, then the apparent size of the moon is smaller than that of the sun, and so you get an annular eclipse that is never total because you can see the edges of the sun around the moon. Answer 3: This NASA website says the eclipse duration is shorter when the shadow falls on the curve of the earth, instead of straight down on the earth: Answer 4:Because of the rotation of the earth, the region on Earth in the umbra will not stay in the umbra forever. That's why the total solar eclipse usually lasts for a few minutes. To have the longest duration of the total solar eclipse, the moon must be as close to Earth as possible. This will make the region in the umbra created by the moon larger, which means longer total solar eclipse. You can think of this in another way, you are walking in the shadow of a building under the sun. If you walk slower or if you can make the building larger (larger shadow), then you will stay longer in the shadow. So when the Earth-Moon distance is smallest, the shadow projected on Earth is larger, then longer total solar eclipse. There are some other factors that will also affect the length of the total solar eclipse, such as the Earth-Sun distance and at which point or region the totality happens on Earth, etc.Click Here to return to the search form.