Lesson Notes By Weeks and Term v4 - SHS 3
BASIC PHYSICS
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BASIC PHYSICS
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Subject: Physics
Class: SHS 3
Term: 1st Term
Week: 9
Grade code: 3.1.1.LI.4
Strand code: 1
Sub-strand code: 1
Content standard code: 3.1.1.CS.3
Indicator code: 3.1.1.LI.4
Theme: MECHANICS AND MATTER
Subtheme: BASIC PHYSICS
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For centuries, we in Ghana, like people all over the world, have looked up at the night sky with wonder. We see countless stars, the moon, and sometimes the faint, milky band of light we call the Milky Way. But what are we actually seeing? We are looking out into the vast universe, a place filled with giant collections of stars, gas, and dust called galaxies. Understanding these structures helps us understand our own place in the cosmos. From our ancient fishermen navigating by the stars to our modern scientists at the Kuntunse Radio Telescope, the study of the sky is part of our past, present, and future.
A. What is a Galaxy?
A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants (like white dwarfs and neutron stars), an interstellar medium of gas and dust, and dark matter. Think of it as a giant city of stars. Our solar system, including the Sun and Earth, is located within a galaxy called the Milky Way. When you see a faint, hazy band of light across the night sky in a very dark place (like in the village, away from the city lights of Accra or Kumasi), you are looking into the dense centre of our own galaxy. B. Main Types of Galaxies
Galaxies are classified based on their visual shape, a system developed by astronomer Edwin Hubble. Spiral Galaxies: Description: These galaxies have a central bulge (a dense ball of older stars), a flattened rotating disk of stars and interstellar matter, and beautiful spiral arms that wrap around the bulge. Composition: The spiral arms are regions of active star formation and contain many young, hot, blue stars, along with gas and dust. The central bulge contains older, yellower stars. Examples: Our own Milky Way and the nearby Andromeda Galaxy.
 Elliptical Galaxies: Description: These galaxies are smooth, featureless, and shaped like an elongated sphere or an ellipse (like a slightly squashed football). They range from nearly circular to very flat. Composition: They contain very little gas and dust, which means there is very little new star formation happening. They are mostly made up of older, cooler, redder stars. Examples: Messier 87 (M87).