Formula - Galaxies

Elliptical Galaxies - The categorization of elliptical galaxies involves measuring the two axis - the longest and the shortest, and using those values to determine just how elliptical one of these things is.
Formula: e = 10 (a-b)/a where:

• e = elliptical value, rounded to the nearest integer
• a = longest axis distance, measured in any sort of units
• b = shortest axis distance, measured in any sort of units
When "a" and "b" are measured they must be measured with the same units! It doesn't matter what units you use, but they need to be the same.

Typical Problems

1. Galaxy NGC 2033 has a long axis that is 74,000 pc long, and a short axis that is 32,000 pc long. What type of elliptical galaxy is it?

Solution: Pop the values into the formula
e = 10 (a-b)/a
e = 10 (74,000-32,000)/74,000
e = 10 (42,000)/74,000
e = 10 (0.57)
e = 5.7, rounded up to 6. The galaxy is a E6 type.

2. Galaxy NGC 4535 has a long axis that is measured as 15.7" long, and a short axis that is 12.3" long. What type of elliptical galaxy is it?

Solution: Different units, but since they are the same (arc-seconds), you can just pop them into the formula
e = 10 (a-b)/a
e = 10 (15.7-12.3)/15.7
e = 10 (3.4)/15.7
e = 10 (0.22)
e = 2.2, rounded down to 2. The galaxy is a E2 type.