Hello bloggers! How are you all doing today? I’m a little bit frustrated. Right now I’m trying to experiment with what I’ve been learning in diff geo. What I want to do is take statelier reentry data and make it into a curve of its position and platitude with respect to time. That way I can get its equation. You see, when a satellite or comet falls towards Earth it’s free falling and the only force excreted on it is gravity (if we ignore winds, which we can do if we go high enough in the atmosphere). And according to general relativity gravity isn’t a force at all but a shape. The gravity around earth is shaped a certain way and that makes things like balls and satellites travel towards the earth. I’ve included a picture of what I think the gravity around Earth looks like (this is only a slice). I’m managed to secure some satellite reentry data but it’s come in the form of a two line element (TLE) which I guess is standard for NASA. But I want longitude, latitude and altitude from this data. I’m having an impossibly hard time making the jump from Right Ascension to a longitude and altitude or whatever it supposed to be. Does anyone know how to do that? Or know anyone who would know?
Monday, August 9, 2010
Tuesday, August 3, 2010
Monday, March 15, 2010
Wednesday, March 10, 2010
Oh here is another interesting property of Hubble’s law that I don’t think I talked about last time. You can use it to set a minimum on the age of the universe. So to review, Hubble discovered that the universe is expanding and he found that the rate at which stuff (stars nebula etc.) is moving away from us is proportional to the distance they are away from us. The further they are away the fast they are receding. And then he graphed his results and found a line. The equation goes something like this: (the speed at which something is moving away from us) = (the Hubble parameter) X (the distance from us to them). This Hubble parameter is sometimes called the Hubble constant but it’s not really constant. It changes with time, that’s why we use the word parameter. There is another really cool aspect of the Hubble parameter, we can use it to tell how old the universe it.
(the Hubble parameter)= (the speed at which something is moving away from us)/ (the distance from us to them)
In math terms this is
H=S/d so if we invert this we get
and if you take any distance (say the distance that a car has travel) and you divide it by the speed that it went at they you know the time it took to get there. So from the inverse of the Hubble parameter give you the time that it took the stuff (stars nebula etc.) to get where is at, thus putting a minimum on the age of the universe. The current accepted value for H is 70.8 ± 4.0 (km/s)/Mpc which give the age of the universe to be 13.8 billion years.
Tuesday, March 9, 2010
Monday, March 8, 2010
Sunday, March 7, 2010
Hey bloggers! We’ve now made the transition to cosmology! And I have a test on General relativity tomorrow oh no! Anyway we’ve already gone over a lot of the stuff that we are talking about in class but I noticed that while I talked about Hubbles law and all (you can read about it here), I didn’t mention Cepheid variable stars. These stars a very interesting in that they blink. Their luminosity literally varies periodically like a lighthouse. But the cool thing is that there is a very linear relationship between it’s period (how fast it’s gets light and then light again) and it’s luminosity (how bright it is). I’ve included a graph to show this relationship. The cool part is the since we know this, if we look out into the sky and see a variable star we can tell how far away it is. How? Well we can see measure it’s period and see how bright it comes across to us. If we know (from the graph) how bright it’s really suppose to be we can calculate how far it. Yay! You may have heard of these stars before but usually they are referred to as standerd candles.