Interpretation of distance mentioned as degrees

  • Thread starter JC2000
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  • #1
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Homework Statement:
1. Consider the sun like a star at a distance of 2 parsecs. When it is seen through a telescope with 100 magnification, what should be the angular size of the star? Sun appears to be (1/2)° from the earth. Due to atmospheric fluctuations, eye cannot resolve objects smaller than 1 arc minute.

OR

Moon is seen to be of (1/2)° diameter from the earth. What must be the relative size compared to the earth?
Relevant Equations:
I know that one parsec is the angle at the vertex which subtends an arc with length 1 AU.
What is the image that comes to mind/meaning behind the above statements where an objects is seen/appears 'to be (angle) diameter of the Earth?

My interpretation is that if the given angle is drawn with one object as the vertex then the diameter of the second object subtends the given angle.(?)
 

Answers and Replies

  • #2
mjc123
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I think the statement is poorly expressed and confusing. "Sun appears to be 1/2° from earth" looks as if it means an apparent separation between sun and earth for some observer, but it actually means that the sun, as seen from earth, has an apparent angular diameter of 1/2°. So does the moon. "Angular size" is the angle subtended at the position of the observer by the diameter of the object.
 
  • #3
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So the vertex of the angle is on the Earth (the observer) and the diameter of the Sun subtends and angle of 0.5 degrees...
 
  • #4
haruspex
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So the vertex of the angle is on the Earth (the observer) and the diameter of the Sun subtends and angle of 0.5 degrees...
Yes.
 

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