The Sun, Stars, and Planets

• The Sun provides light and heat, essential for photosynthesis, the water cycle, and maintaining Earth's climate.
• Nuclear fusion produces energy within the Sun.

Astronomical Phenomena

• The Northern and Southern Lights (Aurora Borealis and Aurora Australis) are caused by charged particles from the Sun interacting with Earth's magnetic field and atmosphere.
• The distance between Earth and the Sun is about 150 million kilometers, or one astronomical unit (AU).

Stars, Planets, and Moons

• Stars emit light through nuclear fusion, while planets reflect light and orbit a star. Both can possess atmospheres.
• "Luminous" means producing its own light; the Moon is visible due to reflected sunlight.
• There are eight planets in the solar system, orbiting in elliptical paths.
• Inner planets (Mercury, Venus, Earth, Mars) are rocky; outer planets (Jupiter, Saturn, Uranus, Neptune) are gas giants.
• The asteroid belt is between Mars and Jupiter; asteroids are spread out.
• A dwarf planet orbits the Sun without clearing its orbital path; Pluto is an example.

Eclipses and Celestial Bodies

• Solar eclipse: The Moon blocks sunlight from reaching Earth.
• Lunar eclipse: Earth blocks sunlight from reaching the Moon.
• Earth is located in the Milky Way Galaxy.
• Size ranking: Universe > Galaxy > Solar System > Star > Planet > Comet.
• Asteroids are rocky bodies, meteoroids are smaller rocky debris, and comets are icy bodies with tails when near the Sun.

Time, Seasons, and Motion

• A day is 24 hours due to Earth's rotation on its axis.
• A year is 365.25 days because of Earth's orbit around the Sun; leap years adjust for the extra time.
• The Sun appears to rise in the East and set in the West due to Earth's west-to-east rotation.
• Earth's 23.5° tilt causes seasons by varying sunlight angles in different hemispheres.

Observing the Night Sky

• Constellations are star patterns named after mythological figures or animals.

The Universe and Star Life Cycles

• The Big Bang Theory explains the universe's origin, about 13.8 billion years ago.
• Stars form from collapsing gas and dust in nebulae; color indicates temperature (blue = hottest, red = coolest).
• After exhausting nuclear fuel, a star can become a white dwarf (small mass), neutron star (medium mass), or black hole (large mass).

Planetary Facts

• Mercury's surface temperatures range from -180°C to 400°C.
• Earth has an atmosphere containing oxygen.
• Pluto is neither a gas giant nor a terrestrial planet.
• Jupiter has the strongest gravitational pull of all planets.
• Saturn has over 1,000 rings.
• Mars appears reddish.
• Uranus rotates on its side (90° axis).