Absolute Magnitude Questions
Try to do these without looking at your notes first!
1. Define the absolute magnitude of a star
2. Explain how it is based on luminosity.
3. State the relation between apparent magnitude m, absolute magnitude
M and distance r.
4. Derive the absolute magnitude equation using the inverse square law
of radiation.
5. For Rigel, apparent magnitude m=+0.3 and absolute magnitude M=-7.5,
calculate the distance to Rigel.
6. The star Sirius has an apparent an absolute magnitude of +1.42 and is
at a distance of 2.64pc. Calculate its apparent magnitude.
7. The star Canopus has an apparent magnitude of -0.72 and is at a
distance of 96 parsecs. Calculate its absolute magnitude.
8. Calculate the absolute magnitude of the Sun given its apparent
magnitude is about -27.
For those that like a challenge…
9. You observe a Cepheid variable star in the Andromeda galaxy whose
brightness varies with a period of 30 days. If its apparent magnitude
varies around a figure of +19.5:a. Calculate the distance to the Andromeda galaxy in light years.
b. What is the absolute magnitude of Andromeda if its apparent
magnitude is +4.4.
If you really, really like a challenge…
c. Express intensity, I, in terms of an object’s luminosity, L and
the distance to that object, r.
d. Estimate how many stars there are in the Andromeda galaxy
assuming each star’s luminosity is equal to that of the Sun.