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

Question

Quizplus · Accepted Answer

To estimate the size in light years (or parsecs or km) of M31, we need both its angular size and distance. From the given image, we can estimate the angular size of M31 to be approximately 3 degrees.

To find the distance to M31, we can use the relationship between distance, size, and angular size:

distance (in parsecs) = size (in parsecs) / angular size (in radians)

Since we don't have the size of M31 in parsecs, we can use its size in light years and a conversion factor:

1 parsec = 3.26 light years

Therefore,

distance (in light years) = size (in light years) / (angular size (in degrees) * 3.26)

Using a known size of M31 (approximately 220,000 light years) and the estimated angular size (3 degrees), we can estimate the distance to M31 to be approximately 2.5 million light years.

Therefore, the best choice is C: its angular size in degrees and its distance in light years (or parsecs or km).

The Diagram Illustrates Physical Size and Angular Size as Seen