Stars and Constellations

• Astronomy is the study of the universe and everything in it, including stars, planets, galaxies, comets and black holes
• The universe contains all galaxies, stars and planets
• The galaxy is a grouping of many planetary systems. There are billions of galaxies in the universe. There are 100 billion stars in the milky way galaxy
• Our Solar System: is composed of planets that revolve around the sun
• The closet planet to the sun is Mercury, while the farthest planet is Neptune.
• Venus is the hottest planet in the solar system because there is a lot of Carbon Dioxide in Venus' atmosphere.
• Terrestrial - small, solid and rocky composition.
• Gas Giant - Mainly gas and dust and are kind of big.
• Comet is an icy body that releases gas as it orbits around the sun (Ice -> Gas)
• Asteroid is a rocky body smaller than a planet that orbits the sun
• Meteor is a strike of line seen when a meteoroid heats up in the atmosphere. (Is trying to get in the Earth)
• Meteoroid is rocky or metallic fragments of an asteroid, comet, or planet. (Still in the atmosphere)
• Meteorite is a meteor fragment that reaches the ground and lands on the earth's surface
• The atmospheric layer's protection creates friction which causes a meteor to be created since friction = makes objects hot.
• The sun: Is 7.5 billion years old star the center of the solar system. Largest object in the solar system. 15 million degrees celcius and is 95 miles from the earth
• Nuclear Fusion: a process that occurs when the nuclei of several atoms combine into one large nucleus
• A star is a massive ball of plasma that emits light. Large ball of gas held together by gravity with a core so hot nuclear fusion occurs.
• Stellar Nebula: cloud of dust and hydrogen gas
• Protostar: hot and dense core with a dusty surrounding
• Main Sequence (Average/Massive Star): where a star spends most of its life. When Hydrogen begins to fuse in the core. An average star remains in the Main Sequence for billions of years, while a massive star remains in the Main Sequence for a few million years.
• Hydrogen becomes helium in the nuclear fusion and because of Helium, the star expands more.
• Size and mass are main factors for stars.
• Nuclear Fusion: Hydrogen becomes Helium. It releases heat and light (energy), which powers stars
• The 2 forces present in a star are Gravity which pulls a star inward causing it to shrink and then collapse. While on the other hand, Pressure is an outward force that counteracts gravity.
• Red Giant/Supergiant: hydrogen fusion stops, causing it to expand. Therefore Gravity becomes the main force.
• Supernova: an explosion which releases a vast amount of heat and light. It is an outburst of energy.
• Some parts can become a neutron star then a blackhole because of the explosion or some can form Nebula's again which can restart the life cycle.
• When energy becomes released even more from the white dwarfs, they become cold therefore it becomes a black dwarf.
• Constellations were used as maps by sailors so they could navigate their way around the world.
• A constellation is a group of stars that make up a pattern or shape. They have been named by humans over time.
• Massive stars have a shorter lifespan because they have a bigger core, which makes the hydrogen fuel deplete faster.
• Pressure = Fusion Rate. A low mass star has low pressure and a low fusion rate which means cooler stars. On the other hand, a high mass star has a high pressure and a high fusion rate which means hotter stars.
• Blackhole: a great amount of matter packed in a very small area. An empty space, hence it has a strong gravitational field.
• Celestial Sphere: an imaginary sphere surrounding Earth, where all celestial objects appear to be located when observed from our planet.
• Zenith: highest/peak point above our head on the celestial sphere. Can be used as a reference point.
• Composition: 75% hydrogen and 25% helium
• Brightness/Luminosity: amount of light that a star radiates. Characterized with Apparent Magnitude and Absolute Magnitude.
• Apparent Magnitude refers to the brightness of stars when observed on Earth.
• Absolute Magnitude is how bright a star would look like if viewed at a distance of 10 parsecs (32.6 light years).
• The brightness of a star depends on the size, temperature and proximity.