"B" can be for a lot of things, like Blueshift. Blueshift is the opposite of redshift. OK, I suppose you want more of an explanation? Blueshift is a shift in the lines of an object's spectrum toward the blue end when it is coming towards you. Redshift is the shift that occurs when the object is moving away from you. The larger the shift, the faster the object is moving. It is like hearing a train's whistle as it approaches and passes you. In this respect, sound waves act the same as light. Of course Black Hole, Big Bang, and Bolide comes to mind, also.
"C" is for Comet, which can brighten up the night sky with their beauty, or for Constellation which are groupings of stars that can form a picture, or for Cosmic Rays which hit the Earth's atmosphere with very high energy, or craters which form when smaller bodies smash into larger ones.
"D" is for Dark Matter. Stuff out there in space that can only be detected by its gravitational effects on other stuff that can be seen.
"E" is for Extraterrestrial. That is what we call anything that does not originate on Earth.
"F" is for Fireball. That would be an extremely bright meteor or bolide (see "B" above)."
"G" is for Galaxy. A galaxy is a huge group of stars. Some have formed a spiral like our own Milky Way galaxy.
"H" is for Hubble's Law which says that the farther a galaxy is from us, the faster it is moving away from us.
I am going to quit now. That was probably a lot more than you wanted to hear or know, but I am not going to give up. Yep, I will finish the alphabet at another time. Just a warning. But for now, have a great day, you hear?