These are my complete notes for Classical Astronomy, covering topics from throughout the progression of Astronomy, from the ancient beliefs of Aristotle and Ptolemy, to the more modern developments that have contributed to our currrent understanding of the cosmos, such as the revelations of Copernicus and Newton.
NOTE: This section differs from other categories on the site and within Astronomy itself, because the Rules are written more narratively and are much less dense in their information. This is only the case for Classical Astronomy, which deals with many of the characters that existed throughout the early developments of Astronomy, like Ptolemy, Galileo, and Kepler.
I color-coded my notes according to their meaning - All numbered notes (which I call rules) are red, and include examples and the basis for understanding a topic. Definitions are written in green, and other important information (such as large-scale drawings that are better visualized than explained) was written in blue. All of this information is preserved on this page, with logical flow and breaks. I use ascii line drawings sparingly - If I can convey information or a graph using an image online, I will do so.
All of the knowledge present in these notes are filtered through my personal explanations for them, the result of my attempts to understand and study them from my classes. In the unlikely event there are any egregious errors, contact me at jdlacabe@gmail.com.
Summary of Classical Astronomy (Complete)
I. Introduction/General Terms.
Astronomy: The study of the objects that use beyond planet Earth and the proesses by which these objects interact with eachother. Organization of a history of the universe, from the Big Bang to the present. "Science is the progress report of the progress report probing of the secrets of the universe" - Charles Bailyn.
Light-Speed: The distance which light travels within one year. This is 9.46 × 10¹² kilometers per year. Light travels through the universe at this constant. The stars outside are only sending their light at lightspeed, so if one is 20 lightyears away, Earth will only see the stars as it looked 20 years previously. Therefore, we can learn about what happened billions of years ago, at the dawn of the universe, by looking at stars farther away.
Astronomical Units: The distance between the Sun and the Earth. Light travels from the sun over 8 minutes to the Earth. 1 year is the length of time it takes the Earth to rotate around the Sun. Our velocity with respect to Earth is zero, but with respect to the Sun, we're moving 110,000 kilometers per second due to the Earth's orbit. This is Relative Motion & Velocity, which is mathematically elaborated on in Classical Physics.
A. Rule 1. There are eight planets that orbit around the sun along with bunches of other bodies like moons, dwarf planets, and whatever. These make up the solar system we live in. Planets are celestial bodies of significant size that orbits a star. If the planet consistently produces its own light, it is a star.
The Sun being our local star, and stars themselves are basically just enormous balls of bglowing gas which generate energy by internal nuclear reactions.
A. Rule 2. All of the stars visible out in the sky are a part of the Mily Way Galaxy - there are hundreds of billions of more stars in our galaxy, and hundreds of billions of galaxies in the Universe. The Milky Way Galaxy is like a giant disk with a small ball in the middle. The space between the stars is actually not completely empty: there is a sparse distribution of gas intermixed with tiny particles called interstellar dust. The gas and dust will collect into huge clouds in the galaxy, which will form the raw material for future star generations. This interstellar dust is extremely sparse, however, so sparse still serves as a great vacuum. Built-up dust is the space smog, blocking the view of more distant regions of the galaxy to Earth.
A. Rule 3. Because of experimental/observational evidence proving that there is some unknown material exerting gravitational force upon space objects, we know there is some "Dark Matter" that cannot be directly observed interfering with everything.
A. Rule 4. While many solar systems only have on star (like ours), many systems are double or triple systems, with 2, 3, or more stars revolving around each other. Several places in the galaxy have so many stars they are called star clusters.
A. Rule 5. All stars die after running out of fuel, because stars can only produce energy as they do while they have some fuel source. The Sun, for example, uses nuclear fusion to create fuel, converting hydrogen into helium, which releases energy in the form of light and heat. When stars die, they explode and their star dust is fed back into the universe for reuse.
Constellation: The 88 patches of sky which humans have deliminated to simplify observations. For example: the Saggitarius Dwarf Galaxy is in the direction of the Saggitarius constellation.
A. Rule 6. The Milky Way Galaxy has many orbiting satellite galaxies that will eventually be incorporated/subsumed by the Milky Way Galaxy itself, such as the Magellanic Clouds and the Sagittarius Dwarf Galaxy. The nearest non-satellite galaxy to the Milky Way is the Andromeda Galaxy (of the Andromeda Constellation), and these two galaxies, along with 50 others nearvy, are called the Local Group, our local galaxy cluster. Most galaxies occur in cluster.
A. Rule 7. Some galaxy clusters themselves from into larger groups, called superclusters. The Local Group is part of the Virgo Supercluster, 110 million lightyears across. Farther aqat, there are quasars
