AS101 Study Guide - Midterm Guide: Tropical Year, Star Cluster, Declination
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Astronomy (Lecture 1) Luke MacKenzie
- Mostly vacuum (empty space)
- Everything we can possibly see is a tiny fraction
The Sun is Our Star:
- massive ball of glowing gas that generates energy through nuclear fusion
- 100x as wide as the Earth
- source of almost all energy on Earth
Planets:
- are less massive than stars
- non-luminous and spherical
- in orbit around a star
Exoplanets:
- over 600 planets confirmed to be orbiting other stars
- thousands of “candidate” exoplanets, observed by the Kepler Space
Telescope
Some planets have satellites (an object in orbit around a planet)
- natural satellites are also known as “moons”
Asteroid:
- a small, rocky object orbiting a star
Comet:
- a small, icy object orbiting the sun
Galaxies: “cities” of the Cosmos:
- a large system of stars, dark matter, gas, and dust, all bound together by
their combined gravity
Nebulae:
- clouds of gas and/or “dust”
- raw materials for new stars from previous generations
Star clusters:
- Open clusters: 1000s of stars
- Globular clusters: 100000s of stars
- Our Sun probably formed in an open star cluster but has since “moved out”
Galaxy groups and clusters:
● a group of galaxies (a few dozen up to thousands) all held together
gravitationally
Many clusters form a Supercluster: