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Astronomy Study Guide
Standard S6E1: Students will explore current scientific views of the universe and how those
views evolved.
Element S6E1.a: Relate the Nature of Science to the progression of basic historical scientific theories
(geocentric and heliocentric) as they describe our solar system and the Big Bang as it describes the formation
of the universe.
 Geocentric theory states that Earth is the center of the solar system
 Heliocentric theory states that the sun is the center of the solar system.
 The great explosion that produced the universe is called the Big Bang.
 Our sun is a star that is part of a family of about 300 billion stars called the Milky Way Galaxy.
 Copernicus suggested that the sun, not Earth, was at the center of the solar system.
 Galileo made several observations that conclude that the sun was at the center of the solar system.
Element S6E1.b: Describe the position of the solar system in the Milky Way galaxy and the universe.
 A light year is the distance light travels in a year. Measured in km, this distance is about 9.5 trillion billion
km.
 The Milky Way Galaxy has a spiral shape. The sun and solar system is located on one of the outer arms
of the galaxy.
 An astronomical unit is the distance between the sun and Earth (150,000,000 km).
Element S6E1.c: Compare and contrast the planets in terms of:
 Size relative to the earth
 Surface and atmospheric features
 Relative distance from the sun
 Ability to support life
(Key Ideas)
 The four inner planets-Mercury, Venus, Earth, and Mars- are small and have rocky surfaces. They are often
called the terrestrial planets.
 Four outer planets-Jupiter, Saturn, Uranus, and Neptune-are much larger than Earth.
 Pluto has a solid surface and a mass mush smaller than that of Earth.
 Observations tell us that Earth is the only planet that can support life as we know it.
 Mars may have been able to support some type of life at one time.
Solar System Data
Planet
Average
Year Length
Gravity (X
Distance from
Diameter (km)
(in Earth
Earth’s)
Moons
the Sun (km)
days/years)
Mercury
58,000,000
4,880
88 days
0.38
Venus
108,000,000
12,100
225 days
0.91
0
Earth
150,000,000
12,760
365 days
1.0
1
Mars
228,000,000
6,790
687 day
0.38
2
Jupiter
778,000,000
143,000
11.9 years
2.53
63
Saturn
1,427,000,000
120,500
29.4 years
1.14
47
Uranus
2,871,000,000
51,100
84 years
0.90
27
Neptune
4,498,000,000
49,500
165 years
1.14
13
Pluto
5,906,000,000
2,390
248 years
0.8
1
Element S6E1.d: Explain the motion of objects in the day/night sky in terms of relative position.
 Earth’s rotation on is axis causes day and night.
 One complete revolution of Earth around the sun is called a year.
 A constellation is a pattern of stars that ancient people pictured as mythological characters, animal, and other
objects.
 Earth’s revolution around the sun together with its rotation on its axis makes you think the stars change
positions in the sky from night to night.
Element S6E1.e: Explain that gravity is the force that governs the motion in the solar system.
 Gravity is the force that attracts objects to one another.
 The strength of gravity depends on two factors: the product of the masses of the objects and the distance
between them.
 All objects in our solar system travel around the sun in paths called orbits. They follow slightly egg-shaped
paths called ellipses.
 Inertia is the tendency of an object to keep doing what they have been doing before an outside force acts on it.
 Planets stay in their orbits because of gravity and inertia. Gravity pulls the object towards the sun, inertia
pushes the object forward.
Element S6E1.f: Describe the characteristics of comets, asteroids, and meteors.
 Comets are made of ice and dust particles.
 Comets are chunks of material called a nucleus.
 Their tails always points away from the sun.
 Asteroids are chunks of rock and metal and orbit the sun like the planets.
 Most asteroids are found in a belt located between Mars and Jupiter.
 Meteoroids are made of rocky materials, metals, or a combination of both, usually from comets or asteroids.
 When a meteoroid plunges to Earth’s atmosphere, it is called a meteor. If it hits the surface, it is called a
meteorite.
S6E2: Students will understand the effects of the relative positions of the earth, moon, and sun.
Element S6E2.a: Demonstrate the phases of the moon by showing the alignment of the earth, moon, and sun.
 The changing shapes of the moon we see are called phases. The phase of the moon you see depends on how
much of the sunlit side of the moon faces Earth.
 The moon shows all of its phases in a cycle that lasts 29.5 days.
 The names of the moon’s 8 phases in order of appearance are: new moon, waxing crescent, first quarter,
waxing gibbous, full moon, waning gibbous, last quarter, waning crescent.
 Since the moon does not produce light, light from the sun reflects off the moon, enabling it to be seen from
Earth.
 Waxing means “increasing.’
 Waning means “decreasing.”
 During a new moon, the moon is between the sun and Earth, you cannot see the moon.
Element S6E2.b: Explain the alignment of the earth, moon, and sun during solar and lunar eclipses.
 There are two types of eclipses.
 The moon goes dark during a lunar eclipse.
 The sun goes dark during a solar eclipse.
 A lunar eclipse occurs when Earth passes directly between the sun and the moon. The Earth casts a shadow
on the moon.
 A lunar eclipse can happen only during full moon.
 A solar eclipse occurs when the moon passes directly between the sun and Earth. The moon casts a shadow
on a part of Earth’s surface.
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A solar eclipse can happen only during a new moon. This is because it is the only time when Earth, the sun,
and the moon are directly lined up with the moon between Earth and the sun.
There is not a lunar or solar eclipse every month because the moon is not always on the same plane as Earth
and the sun.
The moon orbits Earth at an angle.
An eclipse can be total or partial.
A total eclipse occurs when the `moon or sun becomes completely covered.
A partial eclipse occurs when the moon or sun becomes only partly covered.
Element S6E2.c: Relate the tilt of the earth to the distribution of sunlight throughout the year and its effect on
climate.
 Earth’s axis is tilted from its orbit around the sun by 23.5°.
 Earth has seasons because its axis is tilted as it moves around the sun.
 As Earth revolves around the sun, its axis is tilted away from the sun part of the year and toward the sun for
part of the year.
 The cycle of seasons is caused by Earth’s revolution around the sun and the tilt of Earth’s axis.
 Summer solstice (June 21)is the first day of summer in the Northern Hemisphere. At this time, Earth’s North
Pole is tilted a full 23.5° toward the sun. This Hemisphere of Earth has its longest day.
 Autumnal equinox (Sept. 22) signals the first day of autumn. At this point, Earth is neither pointed toward or
away from the sun.
 All parts of Earth have days and nights that are almost equal in length.
 Winter solstice (Dec. 21) is the first day of winter in the Northern Hemisphere and is a point in Earth’s orbit.
Earth’s North Pole is tilted a full 23.5° away from the sun.
 Sunlight strikes areas north of the equator at a greater angle than at any other time of the year.
 Days are the shortest and nights are the longest.
 Vernal equinox (March 20) marks the first day of spring in the Northern Hemisphere
 At this time, Earth is not tilted toward or away from the sun.
 Days and nights are of equal length.
 At the equator, sunlight hits Earth’s surface more directly or at smaller angles.
 Closer to the poles, sunlight hits Earth’s surface at greater angles. Near the poles, energy from the sun is
spread out over a greater area.
 For this reason, areas near the equator have a very warm climate, and areas farther from the equator have
cooler climates.
 Areas farthest from the equator have the coldest climate since sunlight strikes these areas at the greatest angle.