Chapter 15, Section 2: Characteristics of Stars Page 598

Classifying Stars Scientists classify stars according to Color Temperature Size Chemical composition Brightness

Color, Temperature and Size Stars vary greatly in color. Different colors reveal the star’s temperature. Betelgeuse looks reddish; Rigel looks blue-white; our sun appears yellowish.

Color, Temperature and Size Stars vary greatly in size. Giant stars are typically 10 to 100 times larger than the sun and more than 1,000 times the size of a white dwarf.

Electromagnetic Spectrum Electromagnetic radiation is energy that can travel through space in the form of waves.

Increasing Energy

You actually know more about it than you may think You actually know more about it than you may think! The electromagnetic spectrum is just a name that scientists give a bunch of types of radiation when they want to talk about them as a group. Radiation is energy that travels and spreads out as it goes– visible light that comes from a lamp in your house and radio waves that come from a radio station are two types of electromagnetic radiation. Types of EM radiation are: 1. Radio Waves 5. Ultra violet 2. Microwave 6. X-rays 3. Infrared 7. Gamma rays 4. Visible Light

Radio waves: This is the same kind of energy that radio stations emit into the air for you to capture and turn into your favorite Mozart, Madonna, or The Fray tunes. But radio waves are also emitted by other things ... such as stars and gases in space.

Microwaves: They will cook your popcorn in just a few minutes! Microwaves in space are used by astronomers to learn about the structure of nearby galaxies, and our own Milky Way!

Infrared Rays: Our skin emits infrared light (heat), which is why we can be seen in the dark by someone using night vision goggles. In space, IR light maps the dust between stars.

Visible light: This is the part that our eyes see Visible light: This is the part that our eyes see. Visible radiation is emitted by everything from fireflies to light bulbs to stars ... also by fast-moving particles hitting other particles.

Ultraviolet: We know that the Sun is a source of ultraviolet (or UV) radiation, because it is the UV rays that cause our skin to burn! Stars and other "hot" objects in space emit UV radiation

X-Rays: Your doctor uses them to look at your bones and your dentist to look at your teeth. Hot gases in the Universe also emit X-rays.

Gamma Rays: Radioactive materials (some natural and others made by man in things like nuclear power plants) can emit gamma-rays.. But the biggest gamma-ray generator of all is the Universe! It makes gamma radiation in all kinds of ways.

Visible Light Regular visible light is really a combination of several colors. Red Orange Yellow Green Blue Indigo Violet Different gases, when ionized, will give off different color bands of light.

Star Spectrums Astronomers can use line spectrums to identify the chemical elements in a star. Each element produces a characteristic pattern of spectral lines.

Measuring with Light When stars are moving toward Earth, their wavelengths appear to be shortened or shirt toward the blue side of the spectrum When stars are moving away from Earth, their wavelengths appear to be lengthened or shirt toward the red side of the spectrum Site

Brightness The brightness of stars depend upon both its size and its temperature. Its apparent brightness depends on its distance from Earth. The sun, which is only average in brightness, appears to be the brightest, because it is closest.

Absolute Brightness Absolute brightness refers to the brightness of the star as if it were a standard distance from Earth. If we were to place all stars 93 million miles from Earth (the distance away of our sun) we would see that the sun is of only average brightness.

Measuring Distances Because distances in the universe are so large, astronomers use units other than meters to measure distances. Two units of measure that astronomers use are astronomical units and light-years. One astronomical unit (1 AU) is equal to the average distance the Sun is from the Earth or 93 million miles or 150 million kilometers.

Measuring Distances A light-year is the distance a particle of light would travel in one year’s time. It is a measure of distance. Light travels at 186,000 miles per second or 3 X 108 meters per second. In one year, light would travel 5,860,000,000,000 miles or 9,500,000,000,000,000 meters.

Measuring Distance: Parallax Parallax is the apparent change in position of an object when you look at it from different places.

Measuring Distances to Stars Astronomers often use parallax to measure distances to nearby stars.

The Hertzsprung-Russell Diagram Astronomers use H-R diagrams to classify stars and to understand how stars change over time.

End of Section: Characteristics of Stars Read 15.2, Do the section questions 1a – 3c on page 605