Chapter 30 Section 1 Stars, Galaxies and the Universe

Stars-balls of gases that give off a tremendous amount of electromagnetic energy. The energy comes from nuclear fusion. Stars vary in color. Antares-has a slightly reddish glow

Star “Rigel” shines with blue-white color

The star “Arcturus” shines with an orange tint

Our star “Sol” is a normal star and glows yellow.

Stars are made up of different elements in the form of gases. The inner layers are very hot The outer layers are somewhat cooler. Every chemical element has a characteristic spectrum in a range of temperatures. The color will indicate what the element is. Most stars are made of the same elements as Earth except the most common element is different. On Earth it is oxygen and for stars it is hydrogen.

What do you think is the 2nd most common element in stars? Helium The remaining elements that make up stars are: carbon, oxygen and nitrogen—these are in very small quantities.

Temperatures of Stars Blue above 30,000 10 Lacertae

Blue-white 10,000-30,000 Rigel and Spica

White 7,500-10,000 Vega & Sirius

Yellow-white 6,000-7,500 degrees C. Canopus and Procyon are examples:

Yellow 5,000 – 6,000 degrees C. Sun, Capella

Orange 3,500 – 5,000 degrees C. Arcturus and Aldebaran

Red less than 3,500 degrees C Betelgeuse and Antares

Remember that blue stars shine with the hottest temperatures and red are coolest. Blue stars are generally 35,000 degrees C., but some have been as high as 50,000 C. Red stars are the coolest and the average surface temperatures are 3,000 degrees C. Yellow stars, such as our sun, have surface temperatures of about 5,500 degrees C.

Stars vary in size and mass. Dwarf stars are about the size of Earth. Our sun is a medium sized star. (1,390,000 km in diameter). Giant stars can be 1,000 times the diameter of our sun. Most stars that are visible from Earth are medium sized stars and similar to our sun.

A star’s motion actually has to do with it’s closeness to Earth and how fast the star is actually moving. Circumpolar stars—like the ones in the big dipper are always visible. The farther an observer moves from the north pole area to the equator, the less circumpolar stars would be seen.

Actual movements of stars 1. Rotate on their axis. 2. May revolve around another star. 3. Moving away from or toward our solar system. Using the light colors of the spectrum scientists can tell which way the stars are going.

The Doppler effect comes from the movement of the star which seems to shift the light source. A star moving toward Earth are shifted slightly toward blue. This is called a “blue shift”. This is caused by shorter light waves as it moves toward Earth.

Stars moving away from Earth shift their color to the red and are called “red shift”. Red Shifts occur because the wavelengths of light appear to be longer. Distant galaxies have red-shifted spectra which indicates that these galaxies are moving away from Earth.

Are there other types of “red shifts” ? Yes-- A gravitational red shift occurs when light is affected by strong gravitational forces—like those at the surface of a star or in the vicinity of a black hole. A cosmological red shift only begins to affect the light from galaxies at great distances from the earth. This happens due to the expansion of the universe. The expansion causes more distant objects to move away at greater speeds.

What is a “light-year”? The distance that light travels in one year. The speed of light is 300,000 km/s. So light travels about 9046 trillion km in one year. Our closest star next to the sun is called “Proxima Centuari” is 4.2 light-years from Earth

It takes only 8 min. for the light to reach us so we say that the sun is: 8 light-minutes from Earth. When we see Polaris-- AKA the “North star”-- You see it’s light the way it was 700 years ago!

Stellar Brightness: the visibility of a star depends on two things: 1. It’s brightness 2. It’s distance from Earth Two scales are used to describe the brightness of a star Apparent magnitude: the brightness of a star as seen from Earth

See page 780 in your Earth book. Notice that the lower the number of the star on the chart, the brighter it will appear to us. Absolute magnitude: the brightness that a star would have at a distance of 32.6 light-years from Earth---in other words, if all stars were the same distance from Earth this is how they would look. So, the brighter a star actually is, the lower it’s number of absolute magnitude.

The end of chapter 30 section 1