Recent content by O-r-i-o-n

k*r instead of k/(r^2) As you know Kepler's laws are true for simple garvitional fields , but talking about galaxies and stars in it , the gravity isn't the same as the gravity between two "very small" objects. To sum up what Tony873004 and WhyIsItSo said , in situations of this kind the force...

Good , I didn't think of that , thanks but once someone solved this but I was too young to understand what he did He was trying to solve the " m\ddot{r}=-gMm/r^2 " differential equation , but I guess your solution is good , too . Thanks

Yes , their initial velocity is zero . No it's not a homework , the teacher told us how to use Kepler's third law for a big fall like this (for example an asteroid falls to the sun) but in those kinds of cases one object is a lot heavier than the other one. so this question popped in my head...

There are two objects with the distance of r apart . because of the gravity , these two objects start to get closer to each other and then they get to each other (actually they fall on each other) .So my question is how long does it take for them to get to each other? Thank you

M>>m ? What if mass of the planet(s) is a lot less than the star they're orbiting(M>>m)? I don't think the gravity of the second planet effect the other planet's orbit? according to astro 100000 they're in the maximum mean distance condition! so the gravity force is at the minimum.

Thank you all! Got what I needed!

I don't have a specific question about Optical Depth , I just want to know what it is and what are it's uses and why astronomers use it. and about the 275 pages , really? because the number freaked me out so I didn't go to the details :D , thanks I'll check it out

Already read that one , but thanks! I got somethings from that!

275 pages? what would you have sent me if I had said my English is good? :D Thanks man but I needed sth simpler , sthh in high school level (or a little higher)

Hi Everyone! I was wondering if someone could help me with Optical Depth, I read some articles about it but since my English isn't that good I couldn't Get it well! I have some views about the Opacity But when it comes to optical depth I'll get lost :D help!