1. Astronomy Stars, Galaxies, and the Universe

2. What is Astronomy?
Astronomy is the study of the moon, stars, and other object in space
Astronomers study the Universe using telescopes, satellites, probes, as well as manned and unmanned space flights

3. The Universe
Astronomers define the Universe as all of space and everything in it
What’s found in the Universe
Galaxies
Nebulas
Stars
Solar Systems (planets, dwarf planets, moons)
Asteroids, comets, meteors, meteoroids
Dark matter
Does not give off electromagnetic energy and can not be seen directly
Estimated to make up 23% of the Universe’s mass

4. The Origin of the Universe
Astronomers believe that billions of years ago all the matter and energy in the Universe was concentrated into single hot dense point called a singularity
Tremendous amounts of heat and pressure made this point so unstable that it exploded

5. The Big Bang Theory
According to the Big Bang Theory , the Universe began to expand after an enormous explosion of concentrated matter and energy
As it expanded, the Universe cooled
Atoms formed after a few hundred million years
The first stars and galaxies formed after about 200 million years

6. In Support of the Big Bang
Moving Galaxies-
Edwin Hubble discovered that almost all galaxies are moving away from us and from each other
Hubble’s Law- the farther away a galaxy is, the faster it is moving away from us
Cosmic Background Radiation-
The electromagnetic radiation (thermal energy) leftover from the big bang
Detected with a radio telescope in 1965 by Arno Penzias and Robert Wilson

7. Age of the Universe
Can be determined based on measurements of how fast distant galaxies are moving away from us and from the cosmic background radiation
Astronomers estimate
that the Universe is
13.7 billion years old

8. Galaxies A galaxy is a large system of stars and other cosmic bodies
Galaxies are the major features of the Universe
There may be more than 100 billion major galaxies
There are three main types of galaxies

9. Spiral Galaxies
Have a bulge in the middle and arms that spiral outward, like pinwheels
Bright, central nucleus is made up of millions of stars
Spiral arms contain millions of bright, young stars as well as dust and gas
Example: our Milky Way Galaxy
The Milky Way Galaxy is approximately 100,000 light years across. We are located about 25,000 light years from the center, out on one of the spiral arms

10. Elliptical Galaxies
Vary in shape from nearly spherical to flattened disks
Most of the stars are close to the center
Have no arms
Contains billions of stars but little gas or dust
Stars are no longer forming and are generally older than those in the other galaxies

11. Irregular Galaxies Have no definite shape Stars are spread unevenly
Typically smaller than other types of galaxies
Generally have many bright young stars and lots of gas and dust to form new stars

12. Quasars (quasi-stellar objects)
Very bright, distant objects
Many 10 billion light years away
Look almost like stars
Believed to be active young galaxies with enormous amounts of gas revolving around a giant black in their centers

13. Stars
There may be as many as 200 quintillion stars in the universe (200,000,000,000,000,000,000)
Stars are huge spheres of glowing gas
Made up mostly of hydrogen
Produce energy by nuclear fusion
Stars differ in size,
mass, color, composition
temperature, and
brightness

14. Color & Temperature of Stars
The color of stars can be used to determine
their surface temperature
Blue = 35,000°C
White = 10,000°C
Yellow = 6,000°C
Red-orange = 5,000°C
Red = 3,000°C
The temperature at the center
of a star is much greater than
at its surface

15. Stars are divided into 5 main groups according to size
Smallest
Neutron stars- the smallest stars (avg. diameter = 16 km)
White dwarfs- smaller than the Earth (ex. Van Maanen’s star)
Medium-sized stars- vary in size from 1/10 to 10 times the size of the Sun (ex. the Sun & Sirius)
Giant stars- 10 to 100 times as large as the Sun (ex. Aldebara)
Supergiant stars- up to 1000 times larger than the Sun (ex. Rigel & Betelgeuse)
Largest

16. Composition of Stars
Spectroscopes are used to determine the composition of stars
Almost all stars have the same composition
% hydrogen
20 – 30% helium
2% other elements

17. Brightness of Stars
The brightness of a star depends on its size, its surface temperature, and its distance from Earth
Apparent magnitude- the brightness of a star as it appears from Earth
Absolute magnitude- the amount of light a star actually gives off

18. Hertzsprung-Russell Diagram
A chart that shows the relationship between the absolute magnitude and the surface temperature of stars
Astronomers use H-R diagrams to classify stars and to understand how stars change over time
As the absolute magnitude of main sequence stars increases, the temperature increase as well

19. Hertzsprung-Russell Diagram

20. Measuring Distances to Stars
Astronomers use light years to measure distances between stars
A light year is the distance light travels in a year, 9.5 trillion kilometers
Parallax is used to measure distances to nearby stars
Parallax is the apparent change in
position of an object when you look at
it from different places
The star is viewed when Earth is on
one side of the Sun and then six months
later when Earth is on the other side of the Sun

21. Evolution of Stars Stars evolve, or change, over time
The amount of mass a star begins with is the main factor that determines its evolution
The different kinds of stars in the sky represent the various stages in the life cycle of stars

22. Stages in the Life Cycle of Stars
All stars are created from the gases in a nebula
When the contracting gas and dust from a nebula become so dense and hot that nuclear fusion begins, the protostar begins to shine
When a star begins to run out of fuel, its core shrinks and its outer portion expands
The evolutionary path of a star depends on its mass
Medium-sized stars Expand to red giants  white dwarfs  dims to a black dwarf or dead star
Massive stars  Expand to red giants or supergiants  explode in a supernova  become a neutron star or a black hole (depending on initial mass)

23. Possible Evolutionary Paths for Stars

25. Constellations Groups of stars that form a pattern
The revolution of the Earth around the Sun cause different constellations to be seen at different times of the year
Stars located above the north and south poles, called circumpolar stars, appear to move in circles above the horizon each night
Astronomers use constellations as landmarks to locate other objects in the sky

26. Constellations in the Autumn Sky

27. Atomic Spectra and Astronomy
Since each element has a unique atomic spectrum, the lines in a spectrum can be used to identify the elements present in a star or other source in space.
For atoms that are neutral or have lost only one or two electrons (ions), most spectral lines are in the UV, visual or near infrared range.
For highly ionized atoms, the lines are found in the extreme UV or x-ray region.

28. Different wavelengths of light
When a material is heated to high temperatures, it releases energy in the form of light. The frequency of that light is determined by what the material is, as well as its temperature.
Different wavelengths from stars, including our sun, can be mapped to determine what the composition and/or temperature is of a material.

29. Other information available
The relative intensity of lines in a spectrum varies with temperature so the temperature of a star’s surface can be estimated.
The width of the lines depends on the pressure of the gas.
The structure of the lines depends on the magnetic field strength.
Etc.

30. Our sun
One example of how all of this is used is how NASA looks at our sun.
Pictures are taken and colorized since our eyes cannot see the frequency of light that is being measured.

32. Nasa’s Extreme Imaging Telescope images the solar atmosphere at several wavelengths, and therefore shows solar material at different temperatures.