1. Comets, ASTEROIDS, AND mETEORS
Chapter 20, section 5

2. Comets, Asteroids, Meteoroids
There are many smaller objects moving through the solar system classified as comets, asteroids, or meteoroids

3. Comets Comet’s head- the brightest part of the comet
Comet- loose collections of ice, dust, and small rocky particles whose orbits are usually very long, narrow ellipses
You can think of a comet as a “dirty snowball” about the size of a mountain
Comet’s head- the brightest part of the comet
Coma- clouds of gas and dust formed around the outer layer of a comet
When the comet gets close enough to the sun, energy turns the ice into gas
Nucleus- the solid inner core of a comet
Comet’s tail- as a comet heats up, some of its gas and dust stream outward forming a tail
Most comets have two tails, an ice tail and a dust tail, and usually point away from the sun
Comet means “long-haired star” in Greek

4. Comet

5. Origin of comets
Kuiper Belt- a doughnut shaped region that extends beyond Neptune’s orbit to about 100 times Earth’s distance from the sun
Oort Cloud- spherical region of comets that surrounds the solar system out to more than 1,000 times the distance between Pluto and the sun

6. Asteroids
Asteroids- rocky objects that are too small and too numerous to be considered full- fledged planets
Asteroid Belt- the region where most asteroids revolve around the sun; between Mars and Jupiter
Astronomers have discovered more than 100,000 asteroids and are constantly finding more
Scientists believe they are the pieces of the early solar system that never came together to form a planet
65 million years ago one or more large asteroids hit Earth and may have caused extinction

8. Meteoroid
Meteoroid- a chunk of rock or dust in space; come from asteroids or comets
On average a meteor strikes overhead every 10 minutes
Meteor - When a meteoroid enters Earth’s atmosphere, friction with the air creates heat and produces a streak of light in the sky
Meteorites- a meteoroid that passes through Earth’s atmosphere and hit Earth’s surface
Craters on the moon were formed by meteoroids

9. Meteors

10. Constellations
Constellations- a group of stars that forms a pattern in the sky that looks like a familiar object.

11. Constellations
Ancient Greeks and Romans and other early cultures observed patters of stars in the night sky.
Were used as navigation tools.
No GPS!

12. Light-Year Light-Year: The distance light travels in one year.
Travels 300,000 km/second
Or 9.5 Trillion km in one year!

13. Spectrographs
Spectrograph: Breaks the light from an object into colors and photographs the resulting spectrum.
Astronomers use spectrographs to get information about stars, including their chemical compositions and temperatures.

14. Terms Characteristics of Stars
Galaxy: Contains hundreds of billions of stars. (Milky Way)
Universe: All of space and everything in it.
Light-year: Distance that light travels in one year. It is a unit of distance not time.
Parallax: The apparent change in position of an object when you look at it from different places.

15. Classifying Stars Star sizes largest to smallest are:
The main characteristics used to classify stars are: Size, Temperature and Brightness.
Star sizes largest to smallest are:
Super Giant, Giant, Medium, White Dwarf, and Neutron stars.

16. Color and Temperature of Stars
A stars color reveals its temperature. The coolest stars are red and hottest stars are blue, blue-white.
The brightness of a star depends upon its size and temperature.
How bright a star looks from Earth depends on both how far the star is from Earth and how bright the star actually is.

17. Colors of Stars
Hot Stars- - - Blue-White
Cooler Stars- - - Orange-Red

18. Hertzsprung-Russell Diagram
A graph used by astronomers that shows the relationship between surface temperature and brightness of stars.
Most stars (90%) fall under the Main Sequence in which surface temperatures increases as brightness increases.

19. Star Systems and Galaxies

20. Galaxies 3 Main Galaxies: Spiral Galaxies, Elliptical Galaxies
Irregular Galaxies
Spiral: A galaxy that has the shape of twin spirals.
Elliptical: Look like flatten balls.
Irregular: Do not have a regular shape.

21. Big Bang Theory
The initial explosion that resulted in the formation and expansion of the universe.
The universe was small, hot, and dense. It exploded about 10 to 15 billion years ago to make our universe.