Astronomy Review

Lesson 115

There have been a lot of things that have caught my eye in the past week of studying astronomy. I have learned about galaxies (mainly the Milky Way galaxy), black holes (my favourite), and constellations.

I will run you through what I have learned.

Constellations and Asterisms:

Asterisms are arbitrary patterns of stars.

-Con – “together”
-Stellar – “Of or pertaining stars”
-Constellations therefore means “Group of stars”

Technically, a constellation is a region of the sky. And the sky is divided into 88 regions.

The constellation “Ursa Major” (Great Bear) also has the “Big Dipper” in it.

Black Holes:

Black holes are created from an object that has been condensed into a small enough space. That space is called “The Schwarzschild Radius”, and every object has one. If you collapsed the Earth in to it’s Schwarzschild Radius (the size of a peanut), it would become a black hole. The small point, that the object (usually a star that has run out of fuel) collapses to is called the “singularity”.

It’s density is so great, that it’s gravity is so great, that nothing can escape it.

The extraordinary thing about Black Holes is that light can be pulled in by the Black Hole. There is a place in the Black Hole that is called the Photon Sphere where light can actually orbit the Black Hole. And there is also a place called Horizon. That is where the gravity over comes the speed of light and pulls it in. Once something gets too that point, it can’t get back. That is also why you can’t see Black Holes. The light that hits it can’t get out.


Our galaxy is the Milky Way Galaxy, and it is said to orbit around a massive black hole. The type of Galaxy is a Barred spiral galaxy. It is 100,000 — 120,000 light years across and has more than 400 billion stars. There are two outer arms and two inner arms, and a smaller arm that our solar system is in. We can see the centre of our galaxy through a place in the sky called “Baades Window”.

There are so many things in the universe and it is so fun learning about it.

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