Solar Energy to Earth and the Seasons

What is a galaxy?

A group of stars, dust, and gases held together by gravity

What is the size of the Milky Way?

A large spiral galaxy whose disk is about 100,000 light-years wide and about 10,000 light-years thick at the nucleus

Describe the structure of the Milky Way.

The Milky Way has at least three distinct spiral arms, with some splintering

What is a light-year?

A unit of distance, not time, representing the distance that light travels in one year

How fast does light travel?

300,000,000 m/s;
300,000 km/s

How long does it take for us to see light from the following objects?

Alpha Centauri (closest star system to the Sun) - 4.3 years
The Sun - 8 minutes
Andromeda - 2.5 million years

Approximately how many kilometers is one light-year?

9.5 trillion km

What shape is Earth’s orbit around the Sun?

Elliptical (a closed oval path)

What is the plane of the ecliptic?

Plane of Earth’s orbit about the Sun

What is the average distance from the Earth to the Sun?

150,000,000 km

How long does it take for light from the Sun to reach Earth?

8 minutes, 20 seconds

When is Earth’s perihelion to the Sun?

Closest on January 3;
147,255,000 km

When is Earth’s aphelion to the Sun?

Farthest on July 4;
152,083,000 km

How long would it take for Voyager 1 to send a signal to Earth?

1.5 days (36 hours)

What are the four parts the Sun can be divided into?

1. Solar interior

2. Visible surface/photosphere

3. Two atmospheric layers, chromosphere and corona

What is the photosphere?

The region of the Sun that radiates energy to space, or the visible surface of the Sun

What does the photosphere consist of?

A layer of incandescent gas less than 500 kilometers thick

What does the photosphere exhibit?

A grainy texture made of many small, bright markings, called granules, produced by convection

What is the chromosphere?

The first layer of the solar atmosphere found directly above the photosphere

What does the chromosphere consist of?

A relatively thin, hot layer of incandescent gases a few thousand kilometers thick

What does the top of chromosphere contain?

Numerous spicules, which are narrow jets of rising material

What is the corona?

The outer, weak layer of the solar atmosphere

What is a solar wind?

A stream of protons and electrons ejected at high speed from the solar corona

What is a sunspot?

A dark spot on the Sun that is cool in contrast to the surrounding photosphere

Why do sunspots appear dark?

Because of their temperature, which is about 1500 K less than that of the surrounding solar surface

What causes sunspots?

Magnetic storms on the Sun

How long is the activity cycle of sunspots?

11 years

What are prominences?

Huge cloudlike structures consisting of chromospheric gases

What causes prominences?

Ionized gases trapped by magnetic fields that extend from regions of intense solar activity

What is nuclear fusion?

Process in which pairs of hydrogen nuclei are joined, form helium, and emit a large amount of energy

What is energy?

The capacity of a physical system to do work

What is the unit of energy?

Joule (J)

What is solar energy?

Radiant energy (i.e., radiant light and heat) from the Sun

What can produce solar wind?

Sunspots

What helps protect the Earth from solar winds?

The magnetosphere deflects the solar wind towards both of Earth’s poles and only a small portion of it enters the atmosphere and produces auroras

What are auroras?

The result of solar flares;
Are bright displays of light caused by solar radiation interacting with the upper atmosphere in the region of the poles

What is a photon?

A small pocket of light energy

Light can behave as both what?

Waves and particles

What is spectroscopy?

The study of the properties of light that depend on wavelength

What is a continuous spectrum?

An uninterrupted band of light emitted by an incandescent solid, liquid, or gas under pressure

High energy (or shortwave radiation) is associated with ___ temperature.

High

Low energy (or longwave radiation) is associated with ___ temperature.

Low

What is insolation (i.e., incoming solar radiation)?

Solar radiation that reaches a horizontal plane at Earth

What is the solar constant (insolation at the top of the atmosphere)?

1372 W/m²

What is the outer boundary of Earth’s energy system?

The thermopause (480 km above Earth’s surface)

What percentage does the Earth receive of the Sun’s total energy output?

One two-billionth

The tropics receive more concentrated insolation due to Earth’s curvature. They receive how many more times of what poles receive?

2.5 times

What is the subsolar point?

The location where insolation is perpendicular to the surface

What is the formula for net radiation?

Incoming shortwave radiation - outgoing longwave radiation

What is seasonality?

The seasonal variation of the Sun’s position above the horizon and changing daylengths during the year

What are the five reasons for Earth’s seasons?

1. Revolution

2. Rotation

3. Tilt of Earth’s axis

4. Axial parallelism

5. Sphericity

Explain revolution.

Earth revolves around the Sun.
Voyage takes one year.

Explain rotation.

Earth rotates on its axis once every 24 hours.

Explain the tilt of Earth’s axis.

Axis is tilted 23.5 degrees from plane of ecliptic.

Explain axial parallelism.

Axis maintains alignment during orbit around the Sun.
North pole points toward the North Star (Polaris).

Who was the Greek scientific writer, astronomer, and poet who made the first measurement of the size of Earth for which any details are known?

Eratosthenes

Describe the Winter Solstice.

Occurs on December 21 or 22;
Subsolar point at Southern Tropic (23.5 degrees S)

Describe the Spring/Vernal Equinox.

Occurs on March 20 or 21;
Subsolar point at equator

Describe the Summer Solstice.

Occurs on June 20 or 21;
Subsolar point at Northern Tropic (23.5 degrees North)

Describe the Fall/Autumnal Equinox.

Occurs on September 22 or 23;
Subsolar point at equator