Human Understanding of both Earth and Space has Changed Over Time Unit E: Topic One

1.3 The Distribution of Matter in Space

The Big Bang Theory How did it all begin?

Galaxies A grouping of millions or billions of stars, gas, and dust. They are held together by gravity Our galaxy is the Milky Way

Galaxy Sorting activity Look at these images of Galaxies. Work with a partner. Sort the galaxies into groups. Determine How many groups did you have? What are the characteristics of each group?

Galaxies can be classified as spiral, elliptical or irregular

Spiral galaxies Huge; contain stars, gas, and dust Held together by gravity Pinwheel shape (see top view, above) halo is present (see lower view) Rich in gas and dust Young and old stars are present.

Elliptical Galaxies Huge; contain stars, gas, and dust Held together by gravity Round to oval shape Have a bulge, but no disk; halo is present Little cool gas and dust Mainly old stars are present.

Irregular galaxies Huge; contain stars, gas, and dust Held together by gravity No regular shape May show signs of a disk and/or a bulge; halo is present Usually rich in gas and dust Young and old stars are present.

What type of galaxy is the Milky Way? Spiral

What is a star? Hot, glowing ball of gas that gives off light energy Stars vary greatly in their characteristics They can be compared by their surface temperature and their brightness (luminosity) (H-R diagram – next slide) Our sun has a mass 300,000 times greater than earth.

Hertzsprung-Russel Diagram In the 1920s, two scientists, Ejnar Hertzsprung and Henry Norris Russel, began comparing the surface temperature of stars with the stars’ brightness (luminosity). When they plotted their data, they discovered that the distribution of star temperature and brightness is not random. Instead, they found that stars fall into several distinct groupings. This observation led to current theory of how stars evolve and change over very long periods of time.

The Birth of a Star Like people, stars are born, they grow old and they die. Their birth places are huge, cold clouds of gas (mostly helium and hydrogen) and dust, known as 'nebulae'. The most famous of these is the Orion nebula, which is just visible with the unaided eye. These clouds start to shrink under their own gravity. As the cloud gets smaller, it breaks into clumps. Each clump eventually becomes so hot and dense that nuclear reactions begin. When the temperature reaches 10 million degrees Celsius, the clump becomes a new star. After their birth, most young stars (proto-stars) lie at the centre of a flat disc of gas and dust. Most of this material is eventually blown away by the star’s radiation. Before this happens, planets may form around the central star.

Life cycle of a star Choose a piece of paper. Find your group members. Within your group – create a theory for the life cycle of a star.

Life cycle of a star

InfoBIT Our sun is a very average star in the middle part of its life. How average is it? Stand 1 m away from the wall. This distance represents the Sun’s diameter. At this scale, the diameter of the largest star now known would be 2300m (2.3 km).

Star Groups Constellations – groupings of stars we see as patterns in the night sky. There are 88 recognized constellations by the International Astronomical Union Unofficially recognized groupings are called asterisms. The most common asterism is the Big dipper – it is part of the constellation Ursa Major but it is not a constellation itself.

Cosmic Calendar Activity