Earth under the Astronomical Microscope

70%

The oceans cover _____ of Earth's surface.

21%

No other planet's atmosphere contains more oxygen than Earth's, which has a ___ oxygen content.

Auroras

These emerge when electron fluxes from the magnetosphere of the Earth fall on the atmosphere below, causing oxygen and other atoms to shine.

Glow

The simplest aurora. It looks like thin clouds are reflecting moonlight or city lights.

Arc

Shaped like a rainbow but with no sunlight to make one. A steady or pulsating green arc is the most common type of arc, but sometimes dim red arcs appear.

Curtain

Also called drapery. This spectacular aurora resembles a billowing curtain at a theater, but nature is the star of the show.

Rays

One or more long, thin bright lines in the sky, appearing like faint beams from the heavens.

Corona

High overhead, a crown in the sky, with rays emanating in every direction.

Lithosphere

Our planet's rocky terrain.

Hydrosphere

The water in the oceans, lakes, and elsewhere on Earth.

Cryosphere

The frozen regions — Antarctica and Greenland’s ice caps.

Atmosphere

The air from ground level up to hundreds of miles.

Biosphere

All living things on Earth.

Magnetosphere

Plays a vital role in protecting Earth from many of the dangerous emanations from the Sun.

Earth’s Radiation Belt

Regions where electrically charged particles — bounce back and forth above Earth, trapped in its magnetic field.

Geomagnetic Field

Moving streams of molten iron in the outer core generate a magnetic field that reaches out through the whole planet and far into space.

Cosmic Rays

High-speed, high-energy particles that come from explosions on the Sun and from distant points in space.

Geomagnetic Field

• Makes the needle of a compass point toward north (or south).

• Provides an invisible guidance system for homing pigeons, some migratory birds, turtles, salmon, various ants and bees (among other bugs), and even some ocean-dwelling bacteria.

• Forms the magnetosphere far above Earth.

Mean Solar Time

The length of the day, 24 hours, is the average time it takes for the Sun to rise and set and rise again.

365 days

A year consists of approximately ___, the time that it takes Earth to make one complete orbit around the Sun.

Sidereal Days

Earth turns once in 23 hours, 56 minutes, and 4 seconds concerning the stars.

Sidereal Clocks

Measures sidereal time by registering 24 sidereal hours during an interval of 23 hours, 56 minutes, and 4 seconds of mean solar time.

Universal Time (UT)

Also known as Greenwich Mean Time (GMT); Common standard time, and simply the standard time at Greenwich, England.

Coordinated Universal Time (UTC)

The official international time standard.

Axis

The line through the North and South poles; it isn’t perpendicular to the plane of Earth’s orbit around the Sun.

Polaris

The north star; the star Alpha Ursae Minoris, located in the Little Dipper asterism of the Little Bear constellation, Ursa Minor.

Vernal equinox

On the first day of spring, the Sun crosses from “below” (south) the equator to “above” (north).

Summer solstice

The Sun reaches the farthest point north on the ecliptic.

Autumnal equinox

The Sun crosses the equator going back down south, and fall begins.

Winter solstice

The Sun gets as far south as possible on the ecliptic.

Radioactive Isotopes

It turns into another isotope of the same element, or into a different element, at a rate determined by the half-life of the radioactive substance. If the half-life is 1 million years.

Parent Atoms

The original radioactive isotope atoms.

Radioactive Dating

An approach to date minerals and rocks that makes use of radioactive isotopes.

Volcanism

The eruption of molten rock from within Earth, including the formation of new volcanoes.

Meteorites

These are considered debris from asteroids, and asteroids are thought to be debris from the very early solar system, when the planets first formed.