Light Years, Important People, Galaxies 8th Grade
WHAT IS A GALAXY? A galaxy is a hugegroup of single stars, star systems, star clusters, dust, and gas held together by gravity
How big are galaxies? The largest galaxies have more than a TRILLION stars. There are BILLIONSof galaxies in the universe.
Galaxies • The sun is a star in the Milky Way galaxy. • The sun and its planets are located about 2/3 of the way from the center of the galaxy
3 Types of Galaxies As you look at this image, you will notice many different types of galaxies. Edwin Hubble, the astronomer for whom the Hubble Space Telescope is named, began to classify galaxies in the 1920s, mostly by their shapes. We still use the galaxy names that Hubble originally assigned.
Spiral Galaxies A nucleus of bright stars and two or more spiral arms Spiral galaxies appear to have a bulge in the middle and arms that spiral outward, like pinwheels. The spiral arms contain many bright, young stars as well as dust and gas. Relatively few new starsare forming in the central bulge. The milky way is a spiral galaxy
Elliptical Galaxies Spherical or flattened discs About one third of all galaxies are simply massive blobs of stars. Elliptical galaxies have very bright centers and very little dust and gas. Because there is so little gas, there are no new stars forming, and therefore elliptical galaxies contain only old stars.
Irregular Galaxies NO DEFINITE SHAPE When Hubble first classified galaxies, he had a group of leftovers. He named them “irregulars.” Irregular galaxies are galaxies that do not fit into any other class. As their name suggests, their shape is irregular.
What is a light year? • The distance lighttravels in oneyear *Distances in space are SO GREAT that the numbers we usually use just get too large to work with • Crazy Fact: The milky way galaxy is 150,000 light years across it’s middle • Our Neighbor: The closest galaxy to us, the Andromeda Galaxy, is 2.5 million light-years away
How old is the light? • Light from the sun takes 8 minutes to travel from the sun to Earth • The farther an object is away, the older the light from it!
The sun is about 150,000,000 km away from earth. Why is the light from the sun about 8 minutes old when it reaches your eye?
If the North Star is 360 light years away, it takes 360 years for its light to reach earth. If it is now 2014, the light from the North Star we see now is from the year 1654.
Galileo Galilee • Father of modern astronomy • Improved the telescope • Proved heliocentric model of the universe (sun is the center, not the earth)
Johannes Kepler • Proposed elliptical orbit of planets around the sun • Also said earth revolves around the sun, not the other way around
Edwin Hubble • Classified galaxies by their shape • He is who the Hubble Space Telescope (a REALLY powerful telescope used by NASA) is named after!
Why the controversy? • Both men got in trouble for saying that the earth revolved around the sun! • At the time, many people though the earth was the center of the universe • Why were people so mad?
Why is this important? • Discuss at your tables WHY it is important for people to study the universe • Then discuss WHY it is important for US to LEARN about it!
TOMORROW The CREATION and EXPANSION of the Universe!
Nebula • Galaxies contain giant clouds of gas and dust—we call these clouds nebula. The Latin word for cloud is nebula. • Some types of nebulas glow by themselves, while others absorb light and hide stars. • Still others reflect starlight, creating some awe-inspiring images. • Some nebulas are regions where new stars form. • Spiral galaxies generally contain nebulas; elliptical galaxies do not.