Physical Science 101
Solar Interactions

The Solar System

Revolution of the Earth

The Earth revolves around the Sun
1 sidereal year = 365.25636 days
1 tropical year = 365.24219 days
The orbit is an elliptical path
The orbit defines a plane - Ecliptic Plane
Average orbital velocity = 29.8 km/s
Orbital length = 940,416,480 km
Closest approach to the Sun = 147 million km
Farthest distance from the Sun = 152 million km

Rotation of the Earth

The Earth rotates on its axis One complete rotation = one day 1 day =
Equatorial mean rotational velocity = 0.4651 km/s

Tilt of the Earth

Axis is tilted relative to the ecliptic - 23.5 degrees (23°27') from a perpendicular to the ecliptic
The axial tilt varies between:

Precession of the Axis

At present the Earth's axis appears to point towards Polaris (North Star)
Over time the axis moves - precesses


Seasons are caused by variations in the amount of solar radiation received
Controlled by two main factors


The Circle of illumination passes through the Earth's axis; each hemisphere is equally illuminated
Subsolar Point is located at the Equator
Subsolar Point is the point on the Earth's surface where the sun's rays are perpendicular to the surface
Vernal Equinox:
Autumnal Equinox:


Circle of illumination is tangent to the Arctic or Antarctic Circle
One hemisphere receives more sunlight than the other
Winter Solstice:
Subsolar point is located on the Tropic of Capricorn
Summer Solstice:
Subsolar point is located on the Tropic of Cancer

Tropic and Arctic Circles

Tropics of Cancer and Capricorn are located at 23.5 degrees N and S Latitude
Marked by the subsolar point on the Solstices
Arctic and Antarctic Circles are located at 66.5 degrees N and S Latitude
Marked by the circle of illumination on the Solstices

Earth's Vital Statistics

Radius 6,371 km
Circumference 40,000 km
Mass 6x1024 kg
Density 5.519 g/cc
Surface Area 510,050,100 km2
Surface Area - land 29.2 %
Surface Area - water 70.8 %
Volume 1,083,157,900,000 km3


The capacity to do work.
Common forms of energy include:
Kinetic Energy:
Potential Energy:

Temperature - Heat

Temperature is a measure of heat
Everything has some measure of heat
Heat is:
The amount of heat in an object is related to how fast the atoms are moving in that object


The study of the behavior of heat and heat transfer.
Heat always flows from warmer areas to cooler areas T
hermal energy flows from areas of higher energy to areas of lower energy
Heat is transferred by:


The transfer of heat through collisions between atoms and molecules.
Metals are good conductors
Poor conductors, like air and rock, are called insulators


Heat transfer due to movement or circulation of a fluid or gas
As a material becomes hot, it begins to rise. Why?
As heat is transferred away from the circulating material, it cools. The cold material has a higher density and sinks down to replace the rising, hot material.
This process occurs in the atmosphere and in the Earth's interior.

Electromagnetic Radiation

Based on variations in the wavelengths of light (radiation)
Each color is part of the visible spectrum
Full Spectrum:
    Gamma Rays: <0.01 nm
    X-rays: 0.01 - 10 nm
    Ultraviolet: 10 - 380 nm
    Visible Spectrum: 380 - 750 nm
    Infrared: 750 nm - 1 mm
    Microwaves: 1 mm - 10 cm
    Radio Waves: >10 cm

4 Laws of Radiation

Blackbody Radiation:
Stefan-Boltzman Law:
Wien's Displacement Law:
Kirchoff Law:

Incoming Solar Radiation

Radiation transmitted by the Sun and received on Earth:
Earth only receives radiation from the Sun on one half of the sphere.
9% ultraviolet radiation
41% visible radiation
50% infrared radiation

Outgoing Radiation: Earth into Space

Approximately 1/3 of all incoming radiation is reflected directly back into space.
Visible, IR and UV radiation are absorbed by Earth, reemitted as infrared radiation.
Radiation is lost to space on both the night side and day side of the sphere.
Three major dips in the outgoing radiation curve occur.
What's Missing?

Heat Budget

Global Radiation Balance: The amount of incoming solar radiation equals the amount of outgoing radiation.
Changes in the amounts of incoming radiation vs. outgoing radiation can have dramatic effects on the global climate.
What happens to solar radiation?

Radiation Pathways

Incoming Radiation
Outgoing Radiation

Net Radiation

The Global Energy Balance is a global average.
Radiation is only received on one half of the globe.
Energy is being lost on all parts of the globe.
Equatorial regions receive more radiation than polar regions.
Polar regions loose more radiation than they receive.
Excess energy from the equator must be moved to the polar regions.