Astronomy Review
Indicate areas of focus for test
The Earth’s sun is an average-sized star. The Sun is more than a million times greater in volume
than the Earth.
Life on Earth is dependent on the energy produced by the Sun.
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.
Our solar system is quite small compared to the vastness that reaches out beyond Pluto.
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 nearly circular.
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:
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the mass of the objects
the distance between them
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.
day- 24 hours caused by the rotation of the Earth
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.
eclipse - the partial or total blocking of an object by another
o solar Moon blocks Sun
o lunar Earth blocks Moon
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 latitude/longitude coordinate system and our system of time are based on celestial observations.
Early Astronomers were able to look to the
constellations to determine that the earth was
moving at a predictable rate.
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 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
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the earth rotates on its axis once every 24 hours, causing day and night
revolution (revolve) – the movement of objects around another object
orbit the path of an object as it revolves around another object in space
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the earth revolves around the sun once every 365 ¼ days (a year) causing seasons
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
Winter Solstice (December 21)- the shortest day of the year
Vernal Equinox (March 21)- equal day/night
Autumnal Equinox (September 21)- equal day/night
The shape of Earth, the other planets, and stars are nearly spherical.