Recent content by Singlau

Do you mean the shell is doing CNO cycle in red giant stage? Then is it using PP chain or CNO cylcle in subgiant stage(i. e. First ignition)?

Yes indeed subgiants are going to be red giants eventually. The graph I showed is a model for a star slightly larger than sun. What I'm curious about is the quick turn off from subgiant branch to red giant branch. For every other turn offs in the graph it has a trigger event: e. g. Main...

The photo is the rotation curve of galaxies, you can see the velocity is nearly flat. Then how do people measure velocity dispersion(sigma)? And the other question is why does larger central mass implies larger sigma. I primarily comprehend it like this: the larger the central mass, the larger...

Actually when I first learned stellar evolution two years ago, I directly skipped from main sequence to red giant, omitting subgiant, as most people regard it 'minor. But I read some articles that says the ignition point of hydrogen shell is the turnoff point from the main sequence (i. e. Start...

The path on an HR diagram after a star leaves the main sequence stage is known as post-main sequence evolution. In the graph, it consists of 2 parts: sub-giant branch and red giant branch. The near-horizontal is the former one, and the near-vertical is the latter one. Subgiants are...

It seemed to have been asked before, but I am still a bit confused. How is the velocity dispersion formed? Doesn't the evidence of dark matter tells us that the orbital speed is uniform in a galaxy? Is there a direction of dispersion? (e. g velocity gets larger to the core) And why does...

Earth will not fall into sun because it has inertia, keeping it in orbit. Even if it suddenly loses some inertia, it falls to a lower orbit and won't fall into the sun, as its inertia increase again due to conservation of angular momentum. So, if a thing fall near a black hole, shouldn't it make...

Yes, I know that northern hemisphere is not heated that much. But what I'm saying in the first post is that wind is caused by a rapid decrease of air in southern hemisphere, instead of rapid increase of northern ice. Anyway, now I do understand that the effect on deposition is slower or somehow...

Thanks!

Recently I read a book about Mars, and it says that global sandstorm blows from southern hemisphere to northern hemisphere at perihelion. It's because the southern part is more heated at that position and the closer distance to sun gives it a high temperature, thus sublimating large amount CO2...

It happens at a moment called recombination, where the whole universe suddenly became clear. As universe is broad (or may be infinite), lights from a moment need different time to reach Earth as their sources are at different places.

Hello everyone. I am Sing Lau, a 14-year-old student from Hong Kong. I do astrophotography. At the same time, astronomy theories attract me so much, and raise my infinite number of questions(some stupid). I am here to thank everyone that may answer my questions in the future. Happy Physics! PS...