Solar Energy, Earth-Sun Relationships

Vocabulary-style flashcards covering key terms and definitions from Pages 1–5 on solar system, solar radiation, and Earth-Sun relationships.

Galaxy

A gravitationally bound collection of stars, gas, and dust; billions exist in the observable universe.

Milky Way Galaxy

Our spiral-shaped galaxy containing stars, gas, and dust.

Solar System

The Sun and all objects bound by its gravity (planets, moons, asteroids, comets, etc.).

Gravity

The attractive force between objects; stronger with more mass.

Sun’s mass dominance

The Sun holds about 99.8% of the Solar System’s mass and dominates gravitationally.

Planet

A celestial body that orbits the Sun, is spherical, and has cleared its orbital neighborhood.

Terrestrial (Inner) planets

Rocky, metal-rich planets: Mercury, Venus, Earth, Mars.

Gas/Giant (Outer) planets

Massive planets composed mostly of gas and ice: Jupiter, Saturn, Uranus, Neptune.

Pluto (dwarf planet)

Dwarf planet status since 2006, located in the Kuiper Belt.

Mercury

Closest planet to the Sun; an inner terrestrial planet.

Venus

Second planet from the Sun; terrestrial; notable for its rotation (exception to some rotation rules).

Earth

Our planet; a terrestrial world with atmosphere and life-supporting conditions.

Mars

Fourth planet; terrestrial; known as the red planet.

Jupiter

Largest planet; gas giant with many moons.

Saturn

Gas giant known for its prominent ring system.

Uranus

Ice giant with an extreme axial tilt; rotates on its side.

Neptune

Farthest recognized planet; an ice giant.

8 planets

There are eight planets orbiting the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

146 moons

Number of moons in the Solar System (as noted).

Asteroids

Rocky objects, mostly between Mars and Jupiter.

Comets

Icy bodies with glowing tails that develop when near the Sun.

Kuiper Belt

Region beyond Neptune filled with icy bodies; Pluto is in this belt.

Insolation

Incoming solar radiation intercepted by a surface; measured in W/m^2; depends on sun angle and exposure.

Sun

Center of the Solar System; emits matter and radiant energy.

Solar wind

Outward flow of electrically charged particles from the Sun’s corona; ~400 km/s; reaches Earth in ~4 days; can disrupt satellites; is blocked by magnetic fields.

Aurora (borealis/australis)

Northern/southern lights produced when solar wind energizes atmospheric ions.

Sunspots

Cooler regions on the Sun’s photosphere; appear darker and can be large.

Electromagnetic spectrum

All forms of electromagnetic radiation; energy distributed across wavelengths.

Ultraviolet (UV)

Short-wavelength, high-energy radiation from the Sun.

Visible light

Wavelengths of the spectrum visible to the human eye.

Near infrared

Infrared radiation just beyond the visible range.

Shortwave infrared

Infrared wavelengths invisible to the naked eye; part of the infrared spectrum.

Thermal infrared

Wavelengths longer than about 3 micrometers; emitted by cooler bodies; perceived as heat.

Perihelion

Closest point in a planet’s orbit to the Sun; Earth’s perihelion ~Jan 3 at ~91.5 million miles.

Aphelion

Farthest point in a planet’s orbit from the Sun; Earth’s aphelion ~July 4 at ~94.5 million miles.

Axial tilt

Earth’s axis is tilted about 23.5° relative to its orbital plane and does not rotate about the tilt.

Circle of illumination

Boundary between day and night on Earth; half the globe is illuminated at any time.

Declination of the Sun

Latitude where the Sun’s rays are directly overhead; ±23.5° depending on season.

Subsolar point (SSP)

Point on Earth receiving the Sun’s rays directly overhead at noon.

Tropic of Cancer

Latitude 23.5° N; northernmost latitude where the Sun is overhead at solar noon on solstices.

Tropic of Capricorn

Latitude 23.5° S; southernmost latitude where the Sun is overhead at solar noon on solstices.

Arctic Circle

66.5° N; boundary for polar day/night phenomena in the northern hemisphere.

Antarctic Circle

66.5° S; boundary for polar day/night phenomena in the southern hemisphere.

Summer Solstice

Around June 21/22; Sun’s declination ~23.5° N; NH longest day, SH shortest; equator ~12 hours day/night.

Winter Solstice

Around December 21/22; Sun’s declination ~23.5° S; NH shortest day, SH longest; equator ~12 hours day/night.

Autumnal (September) Equinox

Sun directly overhead at the equator; 12 hours day and night globally; circle of illumination touches poles.

Vernal (March) Equinox

Sun directly overhead at the equator; 12 hours day and night globally.

Equinoxes

Two moments (approx. Mar and Sep) when day and night are equal; sun’s direct rays strike the equator.

Solar altitude

Apparent height of the Sun above the horizon at noon; depends on latitude and solar declination.

Analemma

A figure-eight diagram showing the Sun’s declination over the year.