Chapter 2: Solar Energy to the Earth and the Seasons. Our solar system is located on a remote, trailing edge of the Milky Way galaxy. Our sun is only one of approximately 400 billion stars in the Milky Way.
Our solar system is located on a remote, trailing edge of the Milky Way galaxy. Our sun is only one of approximately 400 billion stars in the Milky Way.
Scientists believe that our solar system condensed from a large, slowly rotating and collapsing cloud of dust and gas known as a nebula.
The explanation of how suns condense from nebular clouds with planetesimals forming in orbits around their central masses is called the planetesimal hypothesis. Scientists developed the hypothesis after observing this type of process using such space-based tools as the Hubble Space Telescope.
Earth’s orbit about the Sun is not perfectly spherical. Instead, it is elliptical, which means that the Earth’s distance from the Sun varies. It is at its closest distance to the Sun (perihelion) in January, and at its furthest distance from the Sun (aphelion) in July.
Another factor that causes a variation in the amount of solar energy reaching the earth is the “tilt” of the earth’s axis. This tilt remains fixed relative to the plane of the ecliptic, which includes all points of Earth’s orbit,
The Sun captured over 99% of the matter from the original nebula, leaving less than 1% to form everything else found in the solar system. As a result, the Sun is the only body in the solar system with enough mass to produce the internal temperature and pressure necessary to sustain a nuclear reaction and produce radiant energy.
While the Sun may appear to be a quiet, glowing ball in the sky, it is actually very active, more closely resembling a boiling sphere of liquid.
There is a constant stream of “solar wind” being emitted by the Sun. This steady flow of clouds of electrically charged particles surges outward in all directions from the Sun. It causes the phenomenon of comets appearing to fly backward as they leave the solar system.
Sunspots are dark areas caused by magnetic storms on the Sun. It has been observed that solar wind grows stronger during periods of increased sunspot activity.
When the solar winds reach the earth, they are deflected toward the poles by Earth’s magnetosphere, so only a small portion reach the atmosphere of the Earth.
The Sun’s radiant energy is composed of roughly 8% ultraviolet, X-ray, and gamma length, 47% visible light, and 45% infrared. It is the difference in wavelengths that causes such phenomena as the sky being blue, and why sunsets are red.
Earth’s atmosphere is divided into layers. The visible evidence of the existence of these layers can only be seen from space.
It was discovered that the seasons result from the variation in the Sun’s altitude above the horizon, declination latitude, and daylength. These are all impacted by the Earth’s revolution about the Sun, the tilt of the Earth upon its axis, and the elliptical shape of the Earth’s orbit.
As you can see, there is a great deal of difference in the angle that the Sun strikes the Sun between the equinoxes and the solstices.
Textbook – “Geosystems: An Introduction to Physical Geography”
Third Edition, by Robert W. Christopherson
The National Aeronautics and Space Administration
The Space Science Laboratory at NASA’s Marshall Space Flight Center
Stanford Solar Center