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Gr. 9 Unit 1
Space
Chapter 10 Notes
Observing Celestial Bodies
Celestial Bodies are natural objects found in space. They include
 Moon
 Sun
 Planets
 Comets
 Asteroids
Constellations are a distinctive pattern in the night sky formed by groups of stars.
 Many are named after Greek and Roman mythology characters.
 88 constellations (20 can never be seen from this hemisphere)
Constellations you need to recognize on a sky chart are:
 Ursa Major, the Great Bear (including the Big Dipper)
 Ursa Minor, the Little Bear -(including the Little Dipper)
 Orion
 Cassiopeia
 Leo
Asterisms are small groups of stars that form a pattern within constellations. The Big
Dipper is a asterism within Ursa Major.
Movement of Celestial Bodies (Sun, Moon, and Planets)
Revolution
 Refers to a planet moving around the sun
Rotation
 Refers to the spin of the planet on it’s axis
Planets, suns and moons move in cyclic paths called orbits (a result of gravitational
forces). They also revolve or rotate around a central axis, while orbiting other celestial
bodies.
The sun follows the same path, called the ecliptic, through the sky every day. The
zodiacal constellations are in this path.
The moon and planets move at different rates along the ecliptic.
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Looking down from the north pole, the earth spins in a counterclockwise direction on an
imaginary line called its axis once every day. This accounts for the fact that the sun rises
in the east and sets in the west.
Movement of Comets and Asteroids
Comets are small bodies made up of rock and ice, their tail may be visible from Earth.
They travel in a long, elliptical orbit around the Sun.
Asteroids are rocky bodies in our solar system. Most asteroids orbit the Sun in a band
between Mars and Jupiter.
Movement Of Stars
Looking southwards the stars move from east (rise) to west (set) during the nightLooking
North stars seem to rotate around Polaris (the north star)
Circumpolar Constellations
Constellations in our north sky (eg. Ursa Major, and Ursa Minor) never appear to go
below the horizon. They just rotate around the Polaris and appear in the North sky all
year.
Seasonal Constellations
Some constellations are visible all year long and some in certain seasons only.
We see different constellations in every season because the Earth moves around the Sun
preventing us from seeing others.
Early Models of the Universe
Human beings have always been curious about the world around them. Early astronomers
built observatories to track the motions of the heavens and developed theories and models
to explain the motions they saw. Examples of this include Stonehenge, in England, and
the Pyramids of Giza, in Egypt.
Contributions to our knowledge and understanding of celestial bodies and their motions
have been made by various individuals. They include:
1) Aristotle
 Visualized the universe as being geocentric (Earth is the centre of the universe
and everything revolves around it).
 He concluded that the Earth was fixed in space and that it was a sphere, due to the
curved edges observed during a lunar eclipse.
2) Ptolemy
 Based his model on his observations of Mars, whose orbital path creates a loop or
s-shape in the sky.
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 His model showed each planet attached to a crystal sphere with its centre at Earth.
Each planet was not attached directly to its sphere but to an off-centre wheel
(epicycle).
 This model was accepted for nearly 1500 years.
Around Ptolemy’s time the astrolab was invented. This instrument was used to locate and
predict the position of the Sun, Moon and stars. It allowed for more accurate observations
to be made.
3) Copernicus
 Believed in a heliocentric universe (Sun at the centre).
 He proposed that the Earth rotated on its axis once daily and revolved around the
Sun once a year.
4) Galileo
 First person to view the “heavens” through a telescope (Allowed him to see
objects about 20x closer)
 He observed: Craters on the Moon, spots on the Sun and four “stars” orbiting
Jupiter (called the Galilean Moons)

Galileo used the scientific method and applied it to astronomy for the first time.
Now that the Sun was placed at the centre of our solar system, other astronomers
could work to understand the motion of the planets. Improvements in the
telescope would show new and strange objects never imagined!
5) Kepler
 He developed 3 Laws of Planetary Motion:
1. All planets move in ellipses with the Sun at one focus.
2. Planets sweep out equal areas of their elliptical orbit in equal times.
3. The time a planet takes to revolve around the Sun is directly related to how far
away it is from the Sun.
6) Newton
 Developed the three laws of motion.
 First to show that the force of gravity affects all celestial bodies, causing them to
stay in orbit

Invented the reflecting telescope, which uses a curved mirror to focus the light to
a point at an eyepiece.
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