Recent content by June_cosmo

Oh I didn't see your reply before. Thanks! You're right. That makes a lot more sense!

Homework Statement (This is a long problem but I think the question is not hard.) Determining the star density from star counts is tough, but estimating counts from a density law is simpler. In practice, this method of fit-ting observed number counts to an assumed density law is becoming a...

Homework Statement https://dept.astro.lsa.umich.edu/~mmateo/Astr404_W16/WebPage/Assignment_Jan21.pdf Homework EquationsThe Attempt at a Solution Apologize for the long question. I was able to solve problem a and b. But for problem c, I was confused. I asked my professor and he gave me this...

Yes, after a second thought I think you're right. I now know how to derive that formula from cosine law. But what about the position angle?

If you look at http://spiff.rit.edu/classes/phys373/lectures/radec/radec.html#radec that @CWatters kindly provided, that would explain a lot.

Actually the "observing point" should be the north or south celestial pole. And I was looking at the webpage too but had no idea how they derived that formula : (

Thank you! I think you're right. But how do I calculate the angular distance from the coordinates?

Homework Statement Go to the following web site: http://www.astro.utoronto.ca/~cclement/cat/listngc.html This is the portal to a large on-line catalog of variable stars in globular clusters. Each link is a cluster name and will take you to a simple text page that lists near the top the...

Thanks! That is helpful!

Homework Statement Within a certain material, an EM wave with = 1 mm is attenuated to 10% of its original intensity after propagating 10 cm. Determine the imaginary part of the index of refraction ni Homework Equations 3. The Attempt at a Solution [/B] so...

Thank you! So that would be \frac{H^2}{H_0^2}=\frac{0.25}{a^3}+0.75,if we combine this with H=\frac{\dot{a}}{a} and I solved this equation (online), it gave me http://www4f.wolframalpha.com/Calculate/MSP/MSP226920fg7hgi3c9658be000033830f2a7886e3e4?MSPStoreType=image/gif&s=20&w=550.&h=47. ...

Oh that's right! So how do I derive a(t) from Friedmann equations?

Homework Statement Numerically integrate and report the particle horizon distance today for the currently fa- vored model \Omega_M=1-\Omega_{DE}=0.25,\omega=-1. Assume the scaled Hubble constant to be h = 0.72, and report the particle horizon in billions of lyr (Gyr). Homework EquationsThe...

I see. Should I use the deceleration formula?

Homework Statement Assume the cosmological model with H0=72,Omega_M=1-Omega_lamda=0.3,(so dark energy with w = − 1) and a flat universe.) a) Find the redshift z at which the universe starts accelerating (that is, when it transitions from decelerating to accelerating). b) How long ago did this...