GEO 130 - Earth-Sun Relationships

Milky Way Galaxy

One of countless star assemblages (galaxies) in the universe

Solar System

The Sun plus its eight orbiting planets, dwarf planets, and other smaller celestial bodies

Why is Earth's location in the Solar System considered unique?

It occupies the habitable zone, with a particular geometric and motional relationship to the Sun

What two things combine to cause Earth's seasons (viewed from space)?

The spatial characteristics of the Earth-Sun relationship, plus Earth's sphericity

Five spatial characteristics of the Earth-Sun relationship

Rotation, Revolution, Eccentricity, Obliquity (axial tilt), and Axial Parallelism (Polarity)

Rotation (definition)

Earth's spinning about its own axis; makes a day

Circle of illumination

The imaginary moving boundary between day and night, caused by rotation

Three effects of Earth's rotation

Diurnal temperature change, the Coriolis Effect, and tidal cycles

Revolution (definition)

Earth's orbiting around the Sun; makes a year

Eccentricity

A measure of how much Earth's elliptical orbit departs from a perfect circle

How long does one revolution (year) take?

365.242 days, in a counterclockwise, uneven-speed elliptical orbit

Perihelion and Aphelion

The two extreme points of Earth's orbit around the Sun (closest and farthest), about 5 million km apart

Obliquity

The tilt of Earth's axis relative to the plane of its orbit

Plane of the ecliptic

The plane containing Earth's orbit around the Sun; forms a 23.44° angle with the plane of the equator

Axial Parallelism (Polarity)

Earth's axis maintains the same alignment, constantly pointing toward Polaris, during revolution

What two local factors determine seasonality from a specific place on Earth?

Changing sun angle (intensity) and day length (duration)

Subsolar point

The point on Earth's surface where the sun is directly overhead; its changing location marks the annual Earth-Sun cycle

Range of the subsolar point's migration

Between 23.44° N and 23.44° S

Winter solstice

When the subsolar point reaches the Tropic of Capricorn

Summer solstice

When the subsolar point reaches the Tropic of Cancer

Vernal equinox

When the subsolar point crosses the Equator moving north; the circle of illumination passes through both poles

Autumnal equinox

When the subsolar point crosses the Equator moving south

Phenology

The study of annual life-cycle events of the biosphere triggered by seasonality

Milankovitch Cycles (definition)

Periodic changes in the Earth-Sun geometric relationship caused by gravitational forces from other planets, supported by paleoclimatic records like ice ages

Orbital Eccentricity cycle (Milankovitch)

The shape of Earth's orbit changes in eccentricity on an approximately 100,000-year cycle

Axial Obliquity cycle (Milankovitch)

Earth's axial tilt shifts between 22.1° and 24.5° and back on a 41,000-year cycle

Axial Precession (Milankovitch)

The wobble of Earth's rotational axis, tracing a circle in the sky every 26,000 years