Christmas Star. There was something different at the end of this year. No, not the lengthy pandemic, even though that is not exactly wrong. It is Jupiter and Saturn that look so close to each other on the sky that they almost look like one bright star, the Christmas Star.
Dark matter is an "invisible" matter can only be detected mainly from its gravitational effect.
Dark matter makes up about ~27% of the universe. What is the effect of dark matter and how is it measured?
Active galactic nucleus (AGN) is a region at the center of a galaxy that is extremely bright.
There are many types of AGNs with distinct appearances and profiles, but they are all thought to be the same object.
Why do they look different, then?