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Chapter 3: Problem 20

How is an annular eclipse of the Sun different from a total eclipse of the Sun? What causes this difference?

Short Answer

Expert verified
An annular eclipse differs from a total eclipse of the Sun in that during an annular eclipse, the Moon doesn't completely cover the Sun, creating a visible ring of sunlight around the Moon. This occurs because the Moon is farther away from the Earth in its orbit (at apogee), and thus appears smaller. In contrast, during a total eclipse, the moon completely covers the Sun as it is closer to Earth in its orbit (at perigee).

Step by step solution

01

Identify the different Eclipse Types

A total eclipse occurs when the Moon completely obscures the Sun, leaving only the solar corona visible from Earth. On the other hand, an annular eclipse occurs when the Moon is in front of the Sun but does not completely cover it, leading to a visible ring (annulus) of sunlight around the Moon.
02

Understand the Causes of the Eclipses

The difference in the visual sizes of the Sun and Moon as seen from Earth is the main cause for these different types of eclipses. This can be attributed to the Moon's elliptical orbit around the Earth.
03

Relate the Moon's Orbit to the Eclipse Type

When the Moon is closer to the Earth (perigee), it appears larger and can cover the Sun completely, resulting in a total eclipse. However, when the Moon is farther from the Earth (apogee), it appears smaller and cannot cover the Sun completely, resulting in an annular eclipse.

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Most popular questions from this chapter

How did Aristarchus try to estimate the diameters of the Sun and Moon?

What is a penumbral eclipse of the Moon? Why do you suppose that it is easy to overlook such an eclipse?

What is the difference between the umbra and the penumbra of a shadow?

Use the Stary Night Enthusiast \({ }^{\mathrm{TM}}\) program to observe the motion of the Moon. (a) Display the entire celestial sphere, including the part below the horizon, by moving to the Atlas mode. You do this by selecting Favourites \(>\) Guides \(>\) Atlas. Here, you will see the sky, containing the background stars and the planets, overlaid by a coordinate grid. One axis, the Right Ascension axis, is the extension of the Earth's equator on to the sky and is marked in hours along the Celestial Equator. At right angles to this equator are the Declination lines at constant Right Ascension, converging upon the North and South Celestial Poles. These poles are the extensions of the two ends of the Earth's spin axis. You can use the Hand Tool to explore this coordinate system by moving your viewpoint around the sky. (Move the mouse while holding down the mouse button to achieve this motion.) Across this sky, inclined at an angle to the celestial equator, is the Ecliptic, or the path along which the Sun appears to move across our sky. This is the plane of the Earth's orbit. (If this green line does not appear, open the Options pane and check that the Ecliptic is selected in the Guides layer.) Use the Hand Tool to move the sky around to find the Moon, which will be close to, but not on, the ecliptic plane. Once you have found the Moon, use the Hand tool to move the Moon to the right-hand side of the main window. On the toolbar across the top of the main window, click on the Time Flow Rate control (immediately to the right of the date and time display) and set the discrete time step to 1 sidereal day. Then advance time in one-sidereal-day intervals by clicking on the Step Time Forward button (the icon consisting of a black vertical line and right-pointing triangle to the far right of the time controls). You will note that the background sky remains fixed, as expected when time moves ahead in sidereal- day intervals. How does the Moon appear to move against the background of stars? Does it ever change direction? (b) Use this Step Time Forward button to determine how many days elapse between successive times when the Moon is on the ecliptic. Then move forward in time to a date when the Moon is on the ecliptic and either full or new. What type of eclipse will occur on that date? Confirm your answer by comparing with Tables 3-1 and \(3-2\) or with lists of eclipses on the World Wide Web.

(a) Suppose the diameter of the Moon were doubled, but the orbit of the Moon remained the same. Would total solar eclipses be more common, less common, or just as common as they are now? Explain. (b) Suppose the diameter of the Moon were halved, but the orbit of the Moon remained the same. Explain why there would be no total solar eclipses.
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