Astronomy is the scientific study of space. It covers a wide range of topics, such as planets and their compositions, how orbits of planets and moons work, studies of both our own solar system and galaxies outside of it, comets and asteroids, asterisms and stars, and so much more. There are countless topics to explore in astronomy, and it overlaps with many other fields of science -- especially physics and chemistry.

Most of my sources come from the college course I took, my textbook for that class, the numerous astronomy books I own, NASA and its affilated websites, and so on. I would like to thank my astronomy professor for being one of the most kindhearted and enthusiastic professors I have ever had the joy of studying under DESPITE all the comments on ratemyprofessor saying otherwise. You have sparked my interest in this subject like nothing else, and if I had the mathematical capabilities, I would have changed my career path.


General Terms to Know

  • Astronomy - The study of the physical world beyond Earth's atmosphere. It's the scientific study of the universe and everything it contains.
  • Galaxy - A cluster of stars bound together and orbiting a common center of mass
  • Universe - Everything. All of space. We only know of one universe.
  • Nebula - A cloud of gas and dust


Space is so vast that astronomers have to use their own units. An Astronomical Unit (AU) is the average distance between the Earth and the Sun (93,000,0000 mi or 1.496x10^8 km). AUs are commonly used in astronomy to measure distances of other planets, among other things.

The Kuiper belt, a ring of Icy objects just outside of Neptune, where Pluto is located, is 30-50 AU away from the sun!

Light years (ly) are also used to measure distance. 1 light year is the distance light can travel in one year (63,240 AU or 9.46x10^12 km). Because of the massive distances in space, this affects the timeline of when we see a star or planet vs. what the planet is doing at that exact same second. For example, because light takes 8.3 minutes to get from the sun to your eyes, you are actually seeing the sun as it was 8.3 minutes ago. This can have bigger effects, such as looking at a star 5,000 ly away, as you are actually seeing the star as it was 5,000 years ago.

Overview of our Solar System

Our solar system is defined as our sun (sometimes referred to as Sol) and everything orbiting it. In our solar system, we have one star (Sol), 8 planets, 5 dwarf planets, and 180+ moons, as well as many asteroids and comets.

Overview of Neighboring Stars and Galaxies

Our galaxy, the Milky Way, is around 100,000 ly across. The nearest star to our solar system is Proxima Centauri which is 4.2 ly away. The nearest galaxy to ours is Andromeda, which is 2.5 million ly away.

Empty Space

Most people think that space is a vaccum, which is technically not true! In between each star, there is an average of about 1 particle per cubic centimeter. For comparison, there are 10^19, or 10,000,000,000,000,000,000, particles per cubic centimeter in the air on earth :)

These particles in space are known as the Interstellar Medium (ISM). They are denser in some areas than in others, and about 99% consists of hydrogen and helium, with the remaining 1% being other gases and dust. You can learn about the ISM on the sidebar to the right.

Rotation and the Sky

Vocabulary and basics

  • Celestial Sphere - The ancient Greeks and Romans believed the Earth was surrounded by a giant crystal sphere with the stars laid flatly on it. In modern times, we know this isn't true, but we keep the celestial sphere as a concept to calculate location of objects in the sky using Right Ascention and Declination (defined below). The Earth is the center of the celestial sphere, and the sphere extends infinitely.
  • Celestial North/South Pole - projections of Earth's north and south pole, its spin axis, onto the celestial sphere.
  • Celestial Equator - projection of Earth's equator onto the celestial sphere.

  • Constellations - An area or region of the sky.
  • Asterism - A pattern of stars. This is what most people mean when they say "constellation".
  • Circumpolar - Region of the sky that never rises or sets for the observer (explained more in depth in the stars section)
  • Ecliptic - Apparent path of the sun in the sky
  • Equinox - When the ecliptic path and the celestial equator cross. These days have equal amounts of sunlight and darkness.
  • Solstice - When the sun is as far north or south as it gets. These days are the longest or shortest.


  • Rotation - a spin. The Earth rotates once per day, from West to East.
  • Revolution - an orbit. The Earth completes one revolution per year around the sun.

sun goes eastward around earth, earths tilt, seasons, ect

solar vs sidreal - explain sidreal day is 4 minutes faster so stars appear earlier each night

Coordinates in the Sky

  • Horizon - The circle around an observer where the sky hits the ground.
  • Zenith - The point directly above the observer in the sky.
  • Nadir - The point directly below the observer.
  • Altitude - Angle above horizon
  • Great Circle - When slicing a sphere, the great circle is the biggest possible circle you can get. The Prime Meridian and the Equator are the two great circles on Earth.

  • Longitude - Measures East and West
  • Latitude - Measures North and South
  • Right Ascension - Celestial equivalent to longitude. Angle measured Eastward in the sky from where the ecliptic intersects the celestial equator in the vernal equinox.
  • Declination - Celestial equivalent to latitude. Measured from celestial equator.
  • Tropic Circles - Farthest points north or south where the sun can be seen in the zenith, or directly overhead. This area runs from around the middle of Mexico/bottom of Libya/middle of India, down to the top of Argentina/top of south Africa/middle of Australia.

    Degrees, Min of Arc, and Sec of Arc are used to measure angles in astronomy.

  • Min of Arc - 1° = 60 min of arc = 60 arcmin = 60'
  • Sec of Arc - 1' = 60 sec of arc = 60 arcsec = 60"
  • Tilt of Earth = 23.5°

Moon orbital cycle

27 days moves east or something

laws of planetary motion

  1. first law - definition
  2. second - def
  3. third - def
Earth's Moon


size and density

atmosphere and magnetic field

rises in east

Phases of the Moon

Overview of phases [chart]

each phase corrosponds with a different time of day for us. [insert chart]

what causes the phases of the moon?

moon phase cycle vs moon orbital cycle


the moon is a wobbly mfer

Synchronous Rotation



what are maria?

type of rock

% of moon - side we see is mostly maria


what are they?

rock types

% of moon


I wrote this down 10 minutes ago but i dont remember what it is

Theories of Formation of the moon

Giant Impact Hypothesis - boom crash pow

others here idk

Our Solar System


our sun, sometimes called sol, and everything orbiting it. consists of 1 sun, 8 planets, 5 dwarf planets, 180+ moons, asteroids and comets


there are requirements for something to be a planet

  1. put them here

Small Overview of Each Planet

there are 4 terrestrial planets and 4 jovian planets. dont worry because i WILL go into more detail about them later

  • mercury
  • venus
  • earth - boring
  • mars
  • jupiter
  • saturn
  • uranus
  • neptune

Dwarf Planets

dwarf planets are defined by blah blah blah. there are 5. just because pluto is a dwarf planet does not make it lesser do not argue about this with me

  • pluto
  • idk
  • idk - boring
  • the oval one
  • idk

Significant Moons in our Solar System

there are many

  • Our Moon, of course!
  • Jupiter's 4 Moons
  • Titan
  • The Moon that could have organisms in its water i forgot what its called

Other Objects in our Solar System

  • asteroid belt
  • comets
  • satellites
Terrestrial Planets


what are they how many are there ect


what makes a planet terrestrial?

common makeup

what are they generally made of



go fucking wild

entomology (????)


temperature, sky color, pressure


makeup, livable?

Craters and Landmarks

History and Important Missions


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i have a book on this one :)

Jovian Planets


what are they how many are there ect


what makes a planet Jovian?

common makeup

what are they generally made of

Why cant we live on them

too many. gas :(


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its fucking MOONS


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finish later