The diagram illustrates physical size and angular size as seen by the observer. We can estimate the size in light years (or parsecs or km) of M31 from
A)its angular size in degrees.
B)its distance in light years (or parsecs or km).
C)its angular size in degrees and its distance in light years (or parsecs or km).
D)It is impossible to estimate the size of M31.

Question

The diagram illustrates physical size and angular size as seen by the observer. We can estimate the size in light years (or parsecs or km) of M31 from 
A)its angular size in degrees. 
B)its distance in light years (or parsecs or km). 
C)its angular size in degrees and its distance in light years (or parsecs or km). 
D)It is impossible to estimate the size of M31.

Quizplus · Accepted Answer

Using the diagram, we can measure the angular size of M31 to be approximately 3 degrees. To estimate the distance to M31, we can use the standard ruler method. By comparing the physical size of M31 (measured in the diagram) to its angular size (measured in degrees), we can calculate its distance. Assuming the physical size of M31 is 100,000 light years, we can set up a proportion:

Physical size / Distance = Angular size

Plugging in the values we have, we get:

100,000 ly / Distance = 3 degrees

Solving for distance, we get:

Distance = 100,000 ly / 3 degrees = 33,333 ly/degree

Multiplying this by the angular size of M31 (3 degrees), we get the distance to M31:

Distance = 33,333 ly/degree * 3 degrees = 100,000 ly

Therefore, the size of M31 can be estimated to be approximately 100,000 light years and its angular size is approximately 3 degrees.

The Diagram Illustrates Physical Size and Angular Size as Seen