Lecture 2

Vocabulary flashcards covering the origin of the universe, solar system dynamics, planetary classification, and Earth's compositional structure.

Big Bang Theory

The theory that the universe began with an episode of rapid expansion from a compact form approximately $13-14$ billion years ago.

Hydrogen and Helium formation

Simple elements that formed within hours of the Big Bang as subatomic particles combined; Hydrogen consists of $1$ proton + $1$ electron, and Helium consists of $2$ protons + $2$ neutrons + $2$ electrons.

Nuclear fusion

The process in the interiors of stars where very high temperatures and pressures fuse hydrogen atoms together to form helium.

Nebula

A rotating disk of cosmic gas and dust that acts as an incubator for new stars and planets.

Exoplanets

Extra-solar planets that revolve around stars other than the sun.

Astronomical Unit (AU)

A unit of measure defined by the roughly $150,000,000\,km$ distance between the Earth and the Sun.

Differential rotation

The phenomenon where the Sun's equatorial region rotates faster ($25$ days) than its polar regions ($36$ days), disrupting the magnetic field.

Sunspot cycle

An $11$-year cycle involving variation in the number of sunspots, with energy output being slightly larger during a solar maximum.

Solar wind

A stream of charged particles emitted from the sun's magnetic field traveling at approximately $1,600,000\,km/hr$.

Heliosphere

The volume of space affected by the solar wind.

Aurora Borealis and Aurora Australis

Light displays generated in polar regions by the interaction of solar wind with Earth's magnetic field; Borealis occurring in the Northern Hemisphere and Australis in the Southern.

BYBP

An abbreviation meaning Billion Years Before Present; the solar system began forming $4.6$ BYBP.

Terrestrial planets

Small, rocky planets formed closer to the Sun: Mercury, Venus, Earth, and Mars.

Jovian planets

Large, less dense gas giants formed farther from the Sun: Jupiter, Saturn, Uranus, and Neptune.

IAU Definition of a Planet

An object that orbits a star, is massive enough to be approximately spherical ($\sim 400\,km$ radius), and has cleared the neighborhood around its orbit.

Dwarf planets

A class of objects, including Pluto, that orbit a star and are spherical but have not cleared their orbital neighborhood.

Crust

The Earth's outermost compositional layer composed of lighter elements like silicon and oxygen.

Mantle

The compositional layer between the crust and core, primarily made of oxygen, silicon, and magnesium.

Core

The innermost compositional layer composed of iron and nickel, featuring a solid inner core and a partially melted outer core.

Lithosphere

The rigid outer layer of Earth composed of the crust and the upper, cooler mantle.

Asthenosphere

The plastic, slowly deforming layer in the uppermost part of the mantle located beneath the lithosphere.

Tectonic plates

Large slabs of lithosphere that move over Earth's surface, producing earthquakes, volcanoes, and mountain belts.

Axial tilt

The orientation of Earth's rotational axis at $23.5^{\circ}$ to the vertical, which is the cause of seasonal temperature contrasts.

Insolation

The amount of solar energy reaching Earth's surface, which is greatest at the Equator and least at the Poles.

Greenhouse effect

The process where water vapor and carbon dioxide ($0.038\%$) absorb heat, maintaining Earth's average temperature between $15-18^{\circ}C$.