Intro to Astronomy

Grade 9 Science

Astronomy IntroGrade 9 Science

• The universe is everything that exists, including all matter and energy everywhere.

• The study of what is beyond Earth is called astronomy.

Astronomy IntroGrade 9 Science

History…Geocentric Model• The geocentric model (earth

centered model) was based on an ideas from Aristotle, but refined and finished by Claudius Ptolemy.

• Ptolemy imagined that the solar system was made of perfect circles, but his model also had to explain retrograde motion. He did this by adding smaller perfect circles (epicycles) on the orbital paths of each planet (except for the sun).

Astronomy IntroGrade 9 Science

Heliocentric Model• Nicholas Copernicus with the

help of Galileo proposed a model where the sun is the center of solar system. This model was not well received, but it did explain the retrograde motion better then Ptolemy’s model.

• Johannes Kepler added to Copernicus’s by changing the orbital paths to elliptical instead of circular. This explained the speed changes they observed in the night sky.

Astronomy IntroGrade 9 Science

Origins of the Universe• There are a lot of models and ideas that

exist to explain how the universe came about. The current accepted scientific model is called the Big Bang theory. Which states that the universe started from an infinitesimal point that exploded in a huge release of energy and matter 10 to 15 billion years ago.

• The study of the origin and changes of the universe is called cosmology.

Astronomy IntroGrade 9 Science

• Planets orbit the sun in elliptical orbits which are caused by gravitational forces. Orbital Period is the time it takes for one full orbit. Orbital period increases as the body gets closer to the sun. Along with orbiting, a planet also rotates about a central axis.

Astronomy IntroGrade 9 Science

Planets have two types of motion:Rotation

Revolution

Effect of Earth’s Rotation• Rotation – the spinning of an object around its

axis (an imaginary straight line joining the North Pole to the South Pole)

• The Earth’s rotation around its axis takes 24 hours. The rotation causes day and night.

Astronomy IntroGrade 9 Science

Effect of Earth’s Revolution• Revolution – the movement of one object

travelling around another.• It takes the Earth one year (365 days) to

revolve around the Sun. This allows us to see different stars in different seasons.

• The angle of the Earth’s axis in combination with its revolution cause our seasons.

Astronomy IntroGrade 9 Science

Seasons• Although the Earth’s distance from the Sun

changes slightly as it orbits, the distance is not great enough to cause a substantial change in the climate.

• The tilt of the Earth (23.5o) is what causes the seasons to change.

• During the summer, the Northern Hemisphere is titled towards the Sun, while during the winter the Northern Hemisphere is titled away from the Sun.

Astronomy IntroGrade 9 Science

• Each planet is unique in our solar system. Some of the differences are:– Surface temperature– Density– Combination of chemical elements– Gravitational field strength

Astronomy IntroGrade 9 Science

The Inner Planets (Terrestrial Planets)• 1. Mercury• 2. Venus• 3. Earth• 4. MarsThe Outer Planets (Gas Giants)• 1. Jupiter• 2. Saturn• 3. Uranus• 4. Neptune• 5. Pluto (Dwarf Planet)

MercuryDiameter:4,878km

Mass:0.0553EM

Density:5.43

Gravity:0.284EG

Average Temperature:

400 to -170°C

Venus

Diameter:12,102km

Mass:0.8149EM

Density:5.25

Gravity:0.878EG

Average Temperature:500°C

Earth

Diameter:12,756km

Mass:5.9741024 kg

Density:5.52

Gravity:9.8m/sec2

Average Temperature:15°C

Mars

Diameter:6,786km

Mass:0.1074EM

Density:3.95

Gravity:0.379EG

Average Temperature: -60°C

Jupiter

Diameter:142,984km

Mass:317.938EM

Density:1.33

Gravity:2.4EG

Average Temperature: -140°C

Saturn

Diameter:120,536km

Mass:95.181EM

Density:0.69

Gravity:0.923EG

Average Temperature: -175°C

Uranus

Diameter:51,118km

Mass:14.531EM

Density:1.29

Gravity:0.793EG

Average Temperature: -214°C

Neptune

Diameter:49,528km

Mass:17,135EM

Density:1.64

Gravity:1.122EG

Average Temperature:-214°C

Astronomy IntroGrade 9 Science

Solar System • At the centre of

our solar system is a star, the Sun, that is essential to life on Earth. The sun is the largest body in our solar system.

Astronomy IntroGrade 9 Science