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Astronomy Review
The Earth’s sun is an medium-sized yellow star. The Sun is more than a million times greater in volume than
the Earth.
Other stars are like the Sun but are so far away that they look like points of light. Distances between the stars
are vast compared to distances within our solar system.
The Sun and planets that revolve around it are the major bodies in the solar system. Other members include
comets, moons, and asteroids. Earth’s orbit is an ellipse.
comet- a ball of ice and dust in orbit
moon- the natural satellite of the earth, visible (chiefly at night) by reflected light from the sun
asteroid- objects revolving around the Sun that are too small to be considered planets
Gravity is the force that keeps planets in orbit around the Sun and the Moon in orbit around the Earth.
The amount of gravitational pull is determined by 2 factors:
1. the mass of the objects
2. the distance between them
The latitude/longitude coordinate system and our system of time are based on celestial observations.
0° longitude
Early Astronomers were able to look to the
constellations to determine that the earth was
moving at a predictable rate.
0° latitude
Moons are seen by reflected light. Our Moon orbits Earth, while Earth orbits the Sun. The Moon’s phases as
observed from Earth are the result of seeing different portions of the lighted area of the Moon’s surface. The
phases repeat in a cyclic pattern in about one month.
“d” dying (waning)
“b” born (waxing)
The apparent motions of the Sun, Moon, Planets, and stars across the sky can be explained by Earth’s rotation
and revolution. Earth’s rotation on its axis causes the length of one day to be approximately 24 hours. This
rotation also causes the Sun and Moon to appear to rise along the eastern horizon and to set along the
western horizon. Earth’s revolution around the Sun defines the length of the year to be 365 1/4 days.
rotation (rotate) - the spinning motion of a planet on its axis
 the earth rotates on its axis once every 24 hours, causing day and night
Rotation
revolution (revolve) – the movement of objects around another object
 the earth revolves around the sun once every 365 ¼ days (a year) causing seasons
Revolution
orbit the path of an object as it revolves around another object in space.
Objects in orbit in space remain in orbit because of inertia and the force of gravity
Most objects in the solar system have a regular and predictable motion. These motions explain such
phenomena as a day, a year, phases of the Moon, eclipses, tides, meteor showers, and comets.
a day- 24 hours caused by the rotation of the Earth
a year- 365 ¼ days caused by the Earth’s revolution around the Sun
phases- different shapes of the moon as seen from Earth caused by the changes in the relative positions of the
Earth, Sun, and Moon.
Solar
Lunar
eclipse - the partial or total blocking of an object by another


solar Moon blocks Sun
lunar Earth blocks Moon
moon in the middle
Earth in the middle
tides- the rise and fall of the level of water in the oceans caused by the Moon’s gravitational pull
meteor showers- meteorites entering the Earth’s atmosphere causing streaks of light
comets – become visible on Earth when their orbit brings them closer to the sun
The tilt of Earth’s axis of rotation and the revolution of Earth around the sun cause seasons on Earth. The
length of daylight varies depending on latitude and season.
Summer Solstice (June 21)- the longest day of the year –
sunlight most direct
Winter Solstice (December 21)- the shortest day of the yearsunlight least direct
Vernal Equinox (March 21)- equal day/night
Autumnal Equinox (September 21)- equal day/night