Astronomy: Celestial Bodies and Models

• Astronomy is the study of the universe and everything in it.
• Celestial bodies include the sun, moon, and stars.
• Earth is tilted on its axis by 23.5°, which causes seasons.

Asterism & Constellations

• An asterism is a distinctive star pattern.
• A constellation is a group of stars that forms a pattern or grouping.

Geocentric Model vs Heliocentric Model

• Two models were developed to explain celestial motion: the Earth-centered (Geocentric) model and the Sun-centered (Heliocentric) model.
• Nicolaus Copernicus developed the Sun-centered and accepted model, Heliocentric.
• Newton developed the Universal Law of Gravitation.

Solar Plane

• An imaginary flat disk extends out from the sun's equator.

Celestial Bodies

• Asteroids are minor rocky planets.
• Asteroids are found between Mars and Jupiter.
• Comets consist of dust and ice
• Comets have a bright nucleus and a faint tail, they also point away from the sun.
• Meteors are commonly known as "shooting stars".
• Meteors are not stars and consist of dust and rock fragments.
• Meteorites are remnants of meteors that do not completely burn up.
• Meteorites fall to Earth as solids made of stone or iron.

Sun Features

• Solar prominences are glowing gas that arches into space.
• Sunspots are regions on the sun that are cooler and appear darker.
• Solar flares occur near sunspots.
• Solar flares are high-temperature eruptions of gases.
• The sun is 330,000 times larger than the Earth.
• The photosphere is the region where the sun's light originates.
• The temperature of the photosphere is 6000°C.
• The corona is an irregularly shaped halo around the sun that is visible during a total eclipse as a ring.
• The temperature of the corona is 1,000,000 °C.

Celestial Measurements

• Planets are celestial bodies that orbit a star.
• Retrograde refers to actual or apparent movement opposite the usual east-to-west direction.
• Inner planets include Mercury, Venus, Earth, and Mars, with similar rocky composition.
• Outer planets include Jupiter, Saturn, Uranus, and Neptune, and are similar in their gaseous composition.
• Temperature is measured in Celsius (°C).
• Distance to the sun is measured in Astronomical Units (AU).
• A light-year is a unit to express greater distances in the universe.
• A light-year is beyond our solar system and equals 9.46 trillion kilometers.

Electromagnetic Spectrum

• Arrangement of electromagnetic waves that include visible light.

Star Characteristics

• Luminosity measures the total energy a star radiates per second.
• A yellow star has a temperature of 6000 °C.
• A red star has a temperature of 3000 °C.
• A blue star has a temperature between 20,000 – 35,000 °C.
• A spectroscope collects a star's spectra pattern.
• Dark bands on a star's spectra represent light absorbed by gases in the atmosphere.
• Solar mass is a term used to express the mass of a star.
• Binary stars are two stars that orbit one another.

Hertzsprung-Russell Diagram

• A plot of color on the x-axis and luminosity on the y-axis.
• About 90% of all known stars are in the main sequence, while red giants are not.

Star Creation

• Gravity is how a star is created and can cause them to die.
• Nebulae are the birthplace of stars, made up of dust and gas.
• Gravity pulls the gas and dust together, and, at 1,000,000 °C, fusion turns the star on.
• Fusion is a nuclear reaction that converts hydrogen into helium and is the source of energy for the Sun.

Star Types

• Low mass stars begin as cool red dwarfs.
• Low mass stars use hydrogen slowly (100 billion years) and become hot white dwarfs.
• Intermediate mass stars include the sun and other red giants.
• Fusion occurs over approximately 10 billion years in Intermediate mass stars.
• Hydrogen gets used up and expands, then helium fuses into carbon and a planetary nebula, which cools into a white dwarf star and then to a black dwarf star.
• High mass stars include supergiants.
• Hydrogen fuses into helium faster over a million years in High mass stars, then swell.
• Fusion stops when iron is made, resulting in a supernova.
• High mass stars will become either a neutron star or a black hole, depending on the remnant size.
• Stellar winds reveal fuzzy objects that are called planetary nebula.
• As the mass of stars increase, stellar winds increase.
• A supernova is a huge explosion of a supergiant or high mass star.
• A neutron star has a mass of 1.5 solar mass and a diameter of 20 km.
• Neutron stars are remnants of a high mass star.
• A remaining core of a star must be less than 3 solar masses to be considered a neutron star.
• Black holes are compact and dense objects that light cannot escape.
• Remaining core is greater than 3 solar masses in a black hole.

Galaxy Characteristics

• The Milky Way galaxy includes the Sun and the Earth.
• The Milky Way is made up of 400 billion stars.
• A galaxy is a huge accumulation of stars, gas, and dust held together by gravity.
• Open clusters contain 50-1000 stars along the main band of the Milky Way.
• Globular clusters are made up of 100,000-1,000,000 stars in a spherical shape.
• Globular Clusters do not lie along the main band of the Milky Way.
• The three major types of galaxies are: Elliptical, Spiral, and Irregular.
• Elliptical galaxies are the most common and are football shaped.
• Elliptical galaxies are composed of old stars and very little gas or dust.
• Spiral galaxies are flat pinwheel shaped with spiraling arms from the central region.
• Star formation occurs in Spiral galaxies which are composed of gas and dust and this includes the Milky Way.
• Irregular galaxies are made up of both young and old stars embedded in gas and dust.
• Irregular galaxies do not have a particular shape and are smaller and less common.
• The Milky Way is one of 30 galaxies that make up the cluster called the Local Group.