Our Solar System

Our Solar System

• Our solar system consists of 8 planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
• To be considered a planet, an object must:
  • Be in orbit around a star (like our Sun)
  • Dominate its orbit (i.e., its mass must be greater than anything else that crosses its orbit)
• Our solar system has two main types of planets:
  • Terrestrial planets: Mercury, Venus, Earth, and Mars (smaller, hard, rocky surfaces)
  • Gas giants: Jupiter, Saturn, Uranus, and Neptune (larger, composed of gases and liquids)

Dwarf Planets and Smaller Objects

• Our solar system also consists of smaller objects that orbit the Sun, including:
  • Pluto, a dwarf planet that doesn't meet the new definition of a planet
  • Moons (natural satellites that orbit planets or dwarf planets)
  • Asteroids (small, irregularly shaped objects made of rock and metal)
  • Meteoroids (small pieces of metal or rock)
• Meteoroids can be as small as dust or as large as a car or building
• If a meteoroid enters Earth's atmosphere, it's called a meteor; if it hits the surface, it's called a meteorite

The Kuiper Belt and Oort Cloud

• Beyond the gas giants lies the Kuiper belt, full of dwarf planets, asteroids, and meteoroids
• The Oort cloud marks the boundary of our solar system

Geocentric vs. Heliocentric Views

• The Geocentric Theory: the Earth is at the center of the universe, and all planets revolve around it
• Aristotle placed the Earth at the center of the universe
• Ptolemy advanced the geocentric theory, adding mathematics to support it
• Heliocentrism: the theory that the Earth and other planets revolve around the Sun
• Copernicus developed the heliocentric theory, which was later supported by Galileo

Eclipses

• An eclipse is an astronomical event involving objects casting shadows on each other
• There are two main types of eclipses: solar and lunar
• Solar eclipses occur when the Moon casts a shadow on Earth
• Lunar eclipses occur when the Earth casts a shadow on the Moon
• Eclipses can only occur when the Sun, Earth, and Moon are aligned (in syzygy)
• Solar eclipses can be total, partial, or annular
• Lunar eclipses can be partial or total

Phases of the Moon

• As the Moon orbits the Earth, different shapes appear due to changing sunlight reflection
• The Moon never changes shape, but appears to due to its orbit

Seasonal Change

• Earth has an axis about which it spins, creating day and night
• Earth orbits the Sun, taking one year to complete a revolution
• As the Earth revolves around the Sun, different parts are tilted towards or away from the Sun, causing seasonal changes
• When the Northern Hemisphere is tilted away from the Sun, it experiences winter; the Southern Hemisphere experiences summer
• Areas along the equator get 12 hours of daylight and night consistently throughout the year
• North and south of the equator, the length of day and night changes throughout the year