Atmosphere and Layers of the Planets

The solar system consists of 8 planets, each with its own unique atmosphere:
- Terrestrial planets (Mercury, Venus, Earth, Mars): thin atmospheres, mostly composed of nitrogen and carbon dioxide
- Gas giants (Jupiter, Saturn, Uranus, Neptune): thick atmospheres, mostly composed of hydrogen and helium
Layers of the atmosphere:
- Exosphere: outermost layer, where atmospheric gases escape into space
- Thermosphere: layer where aurorae occur, temperatures increase with altitude
- Mesosphere: layer where meteors burn up, temperatures decrease with altitude
- Stratosphere: layer where ozone layer is present, temperatures increase with altitude
- Troposphere: lowest layer, where weather occurs, temperatures decrease with altitude

Earth's orbit:
- Elliptical shape, with the Sun at one of the foci
- Takes approximately 365.25 days to complete one orbit
- Orbital velocity: approximately 29.78 km/s
Earth's tilt:
- Axis tilted at approximately 23.5° from the plane of the orbit
- Causes seasonal variations on Earth

Rising and Setting of the Sun:
- Due to Earth's rotation, the Sun appears to rise in the east and set in the west
- Angle of the Sun's rays changes throughout the day, affecting the apparent position of the Sun
Rising and Setting of Other Stars:
- Due to Earth's rotation, stars appear to move in the sky
- Some stars are visible in the night sky, while others are below the horizon

Seasonal Variation:
- Caused by Earth's tilt and orbit around the Sun
- Four distinct seasons: spring, summer, autumn, and winter
- Seasons vary in duration and characteristics depending on the hemisphere
Phases of the Moon:
- Caused by the relative positions of the Earth, Sun, and Moon
- Eight distinct phases: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent
Tides:
- Caused by the gravitational pull of the Moon and Sun on the Earth's oceans
- Two high tides and two low tides daily, due to the Moon's orbit
Formation of the Moon:
- Giant impact hypothesis: Moon formed from debris left over after a massive collision between Earth and a Mars-sized object
- Capture hypothesis: Moon formed elsewhere in the solar system and was captured by Earth's gravity
Major Lunar Missions:
- NASA's Apollo program: first human missions to land on the Moon (1969-1972)
- Soviet Union's Luna program: first unmanned missions to impact the Moon's surface (1959) and return lunar samples (1970)

Terrestrial planets (Mercury, Venus, Earth, Mars) have thin atmospheres composed mostly of nitrogen and carbon dioxide
Gas giants (Jupiter, Saturn, Uranus, Neptune) have thick atmospheres composed mostly of hydrogen and helium

Exosphere: outermost layer where atmospheric gases escape into space
Thermosphere: layer where aurorae occur, temperatures increase with altitude
Mesosphere: layer where meteors burn up, temperatures decrease with altitude
Stratosphere: layer where ozone layer is present, temperatures increase with altitude
Troposphere: lowest layer, where weather occurs, temperatures decrease with altitude

Earth's orbit is elliptical in shape with the Sun at one of the foci
It takes approximately 365.25 days to complete one orbit
Orbital velocity is approximately 29.78 km/s
Earth's axis is tilted at approximately 23.5° from the plane of the orbit, causing seasonal variations

The Sun appears to rise in the east and set in the west due to Earth's rotation
The angle of the Sun's rays changes throughout the day, affecting the apparent position of the Sun
Stars appear to move in the sky due to Earth's rotation
Some stars are visible in the night sky, while others are below the horizon

Seasonal variations occur due to Earth's tilt and orbit around the Sun
There are four distinct seasons: spring, summer, autumn, and winter
Seasons vary in duration and characteristics depending on the hemisphere
The Moon orbits the Earth, causing phases of the Moon: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent
Tides are caused by the gravitational pull of the Moon and Sun on the Earth's oceans
There are two high tides and two low tides daily, due to the Moon's orbit

The Moon formed from debris left over after a massive collision between Earth and a Mars-sized object (Giant Impact Hypothesis)
Alternatively, the Moon formed elsewhere in the solar system and was captured by Earth's gravity (Capture Hypothesis)
NASA's Apollo program sent the first humans to land on the Moon (1969-1972)
The Soviet Union's Luna program sent the first unmanned missions to impact the Moon's surface (1959) and return lunar samples (1970)