Because of interstellar dust, astronomers can see at most about 5 kpc into the disk of the galaxy at visual wavelengths. What percentage of the galactic disk does that include? (Hint: Consider the area of the entire disk versus the area visible from Earth. The diameter of the Milky Way Galaxy is approximately 25 kpc.)

Question

Physics

Adyson Cooley

6 March, 00:24

Because of interstellar dust, astronomers can see at most about 5 kpc into the disk of the galaxy at visual wavelengths. What percentage of the galactic disk does that include? (Hint: Consider the area of the entire disk versus the area visible from Earth. The diameter of the Milky Way Galaxy is approximately 25 kpc.)

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Answers (1)

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Jennifer Cooke · Answer 1

96%

Explanation

Let A the total area of the galaxy, is modeled as a disc:

A = πR^2 = π (25 kpc) ^2

And let a be the area that astronomers are able to see:

a = πr^2 = π (5 kpc) ^2

The percentage that can be seen is equal to 100 times the ratio of the areas, of the galaxy and the "visible" part:

P = 100 a/A = (5/25) ^2 = 100/25 = 4%

Therefore, the percentage of the galaxy not included, i. e. not seen is:

(100-4) % = 96%