ok the question is,(adsbygoogle = window.adsbygoogle || []).push({});

Calculate the photons you expect to recieve per Angstrom at the focus of a Cassegrain telescope of aperture 30cm for a star of V magnitude 9.0, observed at a zenith distance of 60 degrees. Assume extinction coefficient of 0.15 magnitudes per airmass, reflectivity at each surface = 90%, wavelength = 5500 Angstrom.

I'm overwhelmed with all the numbers given and cannot find any equations that are useful to this question. If anyone has an idea please give me a hint on where to start or how to approach this question. Thanks in advance.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Astronomy problem

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**