Solar System Overview

The Solar System, Sun, and Earth

• Our solar system is part of the Milky Way Galaxy, a flattened disk containing over 400 billion stars.
• Our solar system is roughly halfway from the Milky Way's center, located in the Orion Spur of the Sagittarius arm.
• The sun, along with the solar system, formed more than 4.6 billion years ago.

Dimensions and Distances

• Light-year: The distance light travels in one year. 1 light-year = 9.5 trillion km.
• Light speed: 300,000 km/s.
• Milky Way Galaxy: 100,000 light-years across.
• Our Solar System: 11 light-hours across.
• Moon: 1.28 light-seconds away.
• Observable universe: Roughly 12 billion light-years in all directions.

Earth's Orbit

• Earth's orbit around the Sun is elliptical.
• Earth’s average distance from the Sun is 150 million km, and light takes 8 minutes and 20 seconds to reach Earth.
• Perihelion: The point in Earth's orbit where it is closest to the Sun (January 3)—147,255,000 km.
• Aphelion: The point in Earth's orbit where it is farthest from the Sun (July 4)—152,083,000 km.

Solar Energy

• Solar energy: Radiant light and heat from the Sun.
• Nuclear fusion: The process that generates solar energy in which hydrogen nuclei are joined, forming helium and releasing energy.

Sunspots

• Sunspots: Dark areas on the Sun’s surface caused by magnetic storms.
• Sunspots are more than 12 times the diameter of Earth.
• Sunspots have a lower temperature than their surroundings.
• Sunspots have an 11-year activity cycle.
• Solar wind: A stream of energetic particles emitted from the Sun’s corona, often associated with sunspots.
• Coronal Mass Ejection (CME): A large burst of plasma and magnetic field from the Sun’s corona.
• Magnetosphere: Earth’s magnetic field that shields the planet from most of the solar wind.

Insolation Receipts and Earth’s Curved Surface

• Insolation: Solar radiation that reaches Earth’s surface.
• The thermopause (480km above Earth’s surface) marks the outer boundary of Earth's energy system.
• Subsolar point: The location on Earth where the Sun’s rays strike directly at 90 degrees.
• The subsolar point moves between the Tropics of Cancer and Capricorn, due to Earth's tilt.
• Locations further from the subsolar point receive more diffuse insolation.

Causes of the Seasons

• Revolution: Earth’s yearly orbit around the Sun.
• Rotation: Earth’s daily spinning on its axis.
• Tilt of Earth’s axis: The axis is tilted 23.5 degrees from the perpendicular to the plane of the ecliptic.
• Equinoxes: Twice a year, the circle of illumination aligns with the lines of longitude, resulting in equal day and night for all locations (March 20/21 and September 22/23).
• Axial parallelism: The tilt of Earth’s axis remains fixed as it orbits the Sun, meaning the North Pole points toward Polaris.
• Sphericity: Earth’s shape, slightly flattened at the poles and bulging at the equator, affects the distribution of solar radiation.

The Four Seasons

• Summer solstice: The day with the longest period of daylight in the hemisphere tilted toward the Sun.
• In the Southern Hemisphere, this occurs on December 21 or 22.
• Winter solstice: The day with the shortest period of daylight in the hemisphere tilted away from the Sun.
• In the Southern Hemisphere , this occurs on June 20 or 21.
• Midnight Sun: When the Sun remains above the horizon for 24 hours during the summer solstice at high latitudes.
• Annual March of the Seasons: Earth’s position in its orbit around the Sun determines the intensity and duration of solar radiation received by each hemisphere throughout the year.

Explore the fascinating characteristics of our solar system, including its formation, dimensions, and the unique relationship between the Earth and the Sun. This quiz covers various aspects of astronomical distances and the intricacies of Earth's orbit. Test your knowledge about the Milky Way Galaxy and beyond!