In 2014, the Mars rover named Curiosity observed the Martian moon Phobos eclipsing most of the Sun as shown in the figure below. Look up the “average” Sun-Mars distance in units of AU and use this value throughout this problem. (a) Using the fact that the Sun subtends an angle of 0.5 degrees from the Earth, determine the angular size of the Sun from Mars. (i.e., use ratios of Earth and Mars properties, instead of just looking up the actual size of the Sun) (b) Find the dimensions of Phobos and its average distance from Mars. Use this to check your answer about the Sun’s angular size, by roughly determining the angular size of the Phobos and seeing that this is somewhat consistent with the eclipse picture below. Ignore details of less than a factor of 2. This is an ungraded review problem on angular size ratios.
Sun as shown in the figure below. Look up the “average” Sun-Mars distance in units of AU and use this value throughout this problem.
(a) Using the fact that the Sun subtends an angle of 0.5 degrees from the Earth, determine the
angular size of the Sun from Mars. (i.e., use ratios of Earth and Mars properties, instead of just
looking up the actual size of the Sun)
(b) Find the dimensions of Phobos and its average distance from Mars. Use this to check your answer about the
Sun’s angular size, by roughly determining the angular size of the Phobos and seeing that this
Calculate the angular size of the Sun from Mars
To determine the angular size of the Sun from Mars, we can use ratios of Earth and Mars properties. We are given that the Sun subtends an angle of 0.5 degrees from Earth.
The average distance from the Sun to Mars can be found by looking up the “average” Sun-Mars distance in units of AU. Let’s assume this value is 1.5 AU.
Using the fact that angular size is inversely proportional to the distance, we can set up the following proportion:
Earth-Sun distance / Earth-Sun angular size = Mars-Sun distance / Mars-Sun angular size
Plugging in the values:
1 AU / 0.5 degrees = 1.5 AU / Mars-Sun angular size.
Plugging in the values:
1 AU / 0.5 degrees = 1.5 AU / Mars-Sun angular size
Rearranging the equation to solve for Mars-Sun angular size:
Mars-Sun angular size = (1.5 AU / 0.5 degrees) * 1 AU = 3 degrees
So, the angular size of the Sun from Mars is 3 degrees.
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