Earth's Rotation, Revolution, and Seasons

Scientific Notation

• Expresses very large or very small numbers

Earth's Tilt

• Earth is tilted at 23.5 degrees relative to its orbit around the Sun
• The tilt is responsible for the changing seasons

Seasons

• Seasons are caused by Earth's tilt and its revolution around the Sun
• Summer occurs when a hemisphere is tilted toward the Sun, leading to longer days and more direct sunlight
• Winter happens when a hemisphere is tilted away from the Sun, resulting in shorter days and less direct sunlight

Equinox/Solstice

• Equinox (Spring & Fall): Day and night are approximately equal and occur around March 21 and September 23
• Solstice (Summer & Winter): The longest and shortest days of the year occur around June 21 and December 21

Rotation/Revolution

• Rotation: Earth spins on its axis in about 24 hours, causing day and night
• Revolution: Earth orbits around the Sun in about 365 days, creating years

The Moon

• Earth's only natural satellite
• Tidal locking: The same side always faces Earth due to the moon's synchronized rotation and revolution
• The moon orbits Earth every 27 days

Lunar Cycle

• The Moon's phases result from its position relative to Earth and the Sun
• Phases: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Third Quarter, Last Quarter, Waning Crescent
• Waning is on the left while waxing is on the right
• One complete lunar cycle takes about 27 days

Eclipse

• Solar Eclipse: The Moon blocks sunlight from reaching Earth during a New Moon
• Lunar Eclipse: Earth casts a shadow on the Moon during a Full Moon

Space Race (Important Dates)

• 1957: Sputnik 1, the first artificial satellite, was launched by the USSR
• 1958: Explorer 1, the first artificial satellite launched by the USA
• 1959: NASA announces the Mercury 7 astronauts
• 1961: Yuri Gagarin was the first human in space, from the USSR
• 1962: John Glenn was the first human to orbit Earth, from the USA
• 1969: Apollo 11, the first Moon landing occurred, from the USA
• Neil Armstrong, Buzz Aldrin, and Michael Collins were the three astronauts on the mission
• 1986: The Space Shuttle Challenger exploded
• 1998: Construction began on the International Space Station (ISS)

Artemis Program

• NASA's mission to return humans to the Moon and establish a lunar base
• Artemis I: Uncrewed test flight (2022)
• Artemis II: First crewed mission (planned for 2024)
• Artemis III: The first woman and person of color is planned to land on the Moon (planned 2025+)

Solar System (Planets)

• Inner Planets: Rocky, terrestrial planets
• Mercury: The only planet without an atmosphere
• Venus: Has an atmosphere made up of Greenhouse Gases
• Earth: The only planet in the solar system with a livable atmosphere
• Mars: Experiences weak winds due to its thin atmosphere
• Outer Planets: Gas giants
• Jupiter: Known for being the largest planet in the solar system
• Saturn: Experiences wind speeds up to 1800 km/h, making it the windiest planet in the solar system
• Uranus: Its axis is greatly tilted, causing it to roll through its orbit
• Neptune: The farthest planet and the most dense of the gas giants

Scale of the Universe

• Vast distances measured in Astronomical Units (AU) or light-years
• 1 AU = distance from Earth to Sun (~150 million km)
• Light-year = distance light travels in one year (~9.46 trillion km)

Asteroids and Comets

• Asteroids: Rocky bodies, mostly in the Asteroid Belt between Mars & Jupiter
• Comets: Made of ice and dust, develop tails when near the Sun Comets come from the Kuiper Belt (more specifically the Oort Cloud), found beyond Neptune

Big Bang Theory

• The leading theory is that the origin of the universe occurred approximately 13.8 billion years ago
• The universe began as a singularity and has been expanding since
• Cosmic Background Radiation is all over the universe and was left over from the Big Bang
• The Universe is still expanding
• The abundance of Hydrogen and Helium (the first elements the Big Bang made)

Gravity

• A force of attraction between objects with mass
• Affects planetary orbits and tides
• Gravity gets stronger as an object's mass increases
• Gravity increases as the distance between objects decreases

Formation of Stars and Galaxies

• Nebula: Cloud of gas and dust where stars form
• Galaxies: Massive collections of stars, gas, and dust held together by gravity (e.g., Milky Way)
• Spiral, Elliptical, Irregular galaxies are types of galaxies

Life Cycle of a Star

• Small stars: Nebula -> Main Sequence -> Red Giant -> Planetary Nebula -> White Dwarf
• Large stars: Nebula -> Main Sequence -> Red Supergiant -> Supernova -> Neutron Star or Black Hole

Hertzsprung-Russell Diagram

• A graph showing the relationship between a star's brightness (luminosity) and temperature
• Main Sequence: Most stars, including the Sun
• Red Giants & Supergiants: Cool but very bright
• White Dwarfs: Hot but dim
• Star colors and temperatures are confusing because blue stars are the hottest, followed by white, yellow, orange, and red stars