The Earth in Space

Overview

Third Rock From the Sun

• The Earth is a rocky or terrestrial planet
• Third from the Sun

Earth is the third planet from the Sun

The Earth has A Diurnal Cycle

• Diurnal means day and night
• Causes by the spin of the Earth on its Axis
• Period = 24 hours

The Diurnal Cycle

The Earth has an Annual Cycle

• The Earth completes one orbit around the Sun is about 365.25 days.

The Earth Has Seasons

• Seasons are caused by the Earth’s 23.5 degrees axial tilt
• The Axial Tilt cause variations on the length of day over the course of a year
• The Axial Tilt also causes variations on the angle of the Sun

Shape: Oblate Sphere

• The Earth is a slightly flattened sphere of average radius 6371 km
• This flattening is caused by the spinning of the axis.

Earth is an Oblate Sphere

Mass, Density

• The mass of the Earth is 5.972 x 10²⁴ kg
• Density is 5.51 gm/cm³

Earth is a

Differentiated Planet

• Differentiated means layered
• For its entire age the most dense material has been sinking to the center
• The less dense material has been rising to the surface
• The least dense material has been escaping to space

Cross-section of the Earth with Densities

Differentiation

• The interior is mostly solid with some dense liquid, and some “partial melt,” somewhat solid and somewhat liquid
• Much of the surface is liquid water
• Above the water is gases, the atmosphere

The Magnetic Field

• The interior of the Earth generates a magnetic field.
• This causes by the motion of the liquid iron outer core with respect to the solid iron inner core.
• Magnetic North is not the same as True (Geographic) North. Presently Magnetic North is in Hudson’s Bay.
• The magnetic field reverses on geologic time scales (average time between reversals is about 1/2 million years, but it varies widely).

Earth’s Magnetic Field

Magnetic North vs. True North

True North is also called Geographic North

Magnetic Declination

Magnetic Declination for Portland Oregon is 15.15º East

Magnetic North is Moving

The Geomagnetic poles are the intersections of the Earth's surface and the axis of a hypothetical bar magnet placed at the center the Earth by which we approximate the geomagnetic field. The magnetic poles are the points at which magnetic needles become vertical

Magnetic North is Reversing

We will come back to this after spring break

Surface

• The surface of the Earth is about 75% ocean.
• The oceans are tidal.

The Surface of the Earth is Mostly Water

Goldilocks Zone

• The location of the Earth and its atmospheric conditions place it in the “Goldilocks Zone,” not too cold, not too hot.
• H₂O exists in all three states of matter:
• Solid ice
• Liquid water
• Gaseous steam

The Goldilocks Zone

The Hydrologic Cycle

Earth has a Moon

• The Moon is pretty big for a moon.
• The Moon shows phases.
• There are lunar eclipses where the Earth’s shadow covers the Moon.
• There are solar eclipses where the Moon’s shadow covers a small portion of the Earth.
• The Moon is in a locked orbit.
• The Moon causes tides.

Tides

• The Earth’s oceans are tidal.
• The tides are caused by the interaction of the Sun and the Moon.
• The effect of the Moon is more pronounced.

The Earth’s Tides

End