Learn: Origins of Modern Astronomy & Solar System

Geocentric vs. Heliocentric model

Geocentric is Earth-centered, while heliocentric is Sun-centered.

Aristotle's proof of Earth's shape

Earth must be a sphere because he saw a curved shadow during a lunar eclipse.

Eratosthenes' contribution

Calculated Earth's circumference to within 500 miles using the angle of the noonday Sun.

Retrograde motion

The appearance that planets stop and reverse direction for weeks or months.

Nicolaus Copernicus

Concluded Earth was a planet and constructed a model putting the Sun at the center.

Johannes Kepler's laws

Three laws of planetary motion: elliptical orbits, varying speeds, and proportional relation between orbital period and distance.

Galileo Galilei's discoveries

Discovered phases of Venus, four large moons of Jupiter, sunspots, and lunar features using a telescope.

Sir Isaac Newton

Proved that gravity combined with straight-line motion results in Kepler's elliptical orbits.

Sidereal day vs. Mean solar day

Sidereal day is one complete 360 rotation (23h 56m 4s); solar day is 1 noon to the next (~24 hrs).

Perihelion and Aphelion

Perihelion is when Earth is closest to the Sun (January); aphelion is farthest (July).

Synodic vs. Sidereal month

Synodic is the Moon's phase cycle (29.5 days); sidereal is its true revolution period (27.3 days).

Solar eclipse condition

Occurs when the Moon moves directly between Earth and the Sun during a new-Moon phase.

Terrestrial vs. Jovian planets

Terrestrial are small, dense, and rocky; Jovian are large, low density, and gaseous.

Nebular theory

Describes the formation of the solar system from a rotating cloud of gas and dust (solar nebula).

Olympus Mons

The largest volcano on Mars, located in the Tharsis bulge.

Jupiter's Great Red Spot

A counterclockwise rotating cyclonic storm in Jupiter's southern hemisphere.

Io's volcanic activity

Io is the most volcanically active body in the solar system due to tidal pulls from Jupiter.

Comet structure

Consists of a nucleus (rocky/metal/frozen gases), a coma (glowing head), and a tail pointing away from the Sun.

Meteoroid vs. Meteor vs. Meteorite

Meteoroid is in space; meteor is in Earth's atmosphere; meteorite is found on Earth's surface.

Carbonaceous chondrites

Meteorites that contain simple amino acids and organic materials, the basic building blocks of life.

Continuous spectrum

An uninterrupted band of color produced by an incandescent solid, liquid, or high-pressure gas.

Absorption (dark-line) spectrum

Produced when white light passes through a cool, low-pressure gas, showing dark lines.

Doppler effect

Apparent change in wavelength due to relative motion; increasing distance lengthens wavelengths.

Refracting vs. Reflecting telescope

Refracting uses a lens to bend light; reflecting uses a concave mirror (nearly all large telescopes).

Radio telescopes

Large telescopes using wire mesh that are less affected by weather and can be used 24 hours a day.

Solar photosphere

The Sun's surface, a layer of incandescent gas under 500 km thick with a grainy texture of granules.

Proton-proton reaction

The nuclear fusion reaction in the Sun's core converting four hydrogen nuclei into a helium nucleus.

Sunspots

Dark regions on the solar surface with cooler temperatures (umbra and penumbra) following an 11-year cycle.