Stars

Stars Our Sun is one type of star Stars create their own light Nuclear fusion in stars generates energy Atoms slam into each other at high temperatures and velocities to form larger heavier atoms Stars have their own life cycle

How can we describe stars? Turn and talk – what characteristics can be used to describe stars? Stars are classified based on: size color temperature luminosity (brightness)

Our Sun Our Sun is merely a spec in the Milky Way galaxy The Sun and Earth are located a little over 1/2 way from center in one of the spiral arms The Milky Way contains about 1 trillion other stars. Sun orbits central Milky Way at about 235 km/s around the center of the galaxy The term “light-year” will be discussed in depth in a later slide. NOTE: The image of the spiral galaxy is a close approximation as to what our galaxy would look like from an outsider. The arrow points to our solar system approximate location 2/3 distance out from galactic core. You are here!

Stars Types Colors protostar Blue (hottest) main sequence blue-white dwarf giant super giant neutron Colors Blue (hottest) blue-white white yellow red-orange Red (coolest) TYPES: protostar = new born star just beginning its development main sequence = stable star like our sun dwarf star = small, dying star giant star = stars that are 10 to 100 times larger than our Sun super giant = stars that are 30 to 500+ times larger than our sun neutron star = remains of a collapsed star; very small, hot and massive (~ 30 km diameter with 1 teaspoon of neutron star weighing about 10 million tons) COLORS: represent star temperature listed here in order from hottest to coolest

Stars: Life Cycle—medium size (Sun) Nebula = large area of gas & dust where stars are born. (protostar) Main sequence star = stable, longest stage Red giant = star grows, but cools White dwarf = (eventually will be a Dead Star) Fusion is no longer occurring. The star continues to shine because it is so hot. Nebula =

Stars: Life Cycle - Massive and Super Massive Stars nebula = large area of gas & dust where stars are born (Protostar) main sequence = stable, longest stage red supergiant = star grows, but cools NOTE: Neutron stars that rotate very rapidly and giving off pulses of radio waves are called “pulsars” ***The diameter of a neutron star, made mostly of neutrons, is about 10 km & the mass of 1 teaspoon full of neutron star would be about 500 million tons!!!

Stars: Life Cycle - Massive and Super Massive Stars 4. supernova = star blows off outer portion of gasses 5. neutron star = very small, hot star that develops from a massive star 6. black hole = so small and dense, that even light cannot escape its gravitational pull. They develop from Super Massive Stars

Life Cycle of a Star

Let’s Check… Stars are classified by 4 major things: What are they? What diagram do we use to compare stars? The 4 major colors of stars are _?_. Will our Sun go supernova? Why or why not? temperature, color, type (size), and brightness HR Diagram Blue, white, Yellow, red No, it is too small: It will grow into a red giant and will be large enough to engulf the inner planets in about 5 million years.

Magnitudes of Stars We use telescopes to observe and measure light from stars Magnitude = brightness of a star Absolute magnitude – a measure of the light actually given off by a star Apparent magnitude – a measure of the amount of light received on Earth from a star

So we learned about the big bang Theory which says everything is Expanding away from each other In the universe…. How do we know This is true? We know the universe is expanding because of the red shift… introduce this to students using the next slide with a video link.

How we know… Edwin Hubble

The Electromagnetic Spectrum Energy moves in uniform patterns called waves. The electromagnetic spectrum consists of the range of all possible frequencies of electromagnetic radiation. Wave lengths in this spectrum cover radio waves and light rays. Electromagnetic Waves: Do not need a medium (matter) to travel through

This is a great chart comparing EM spectrum information…not the association between wavelength and approximate equivalent size. Also, note that the LIGHT we see is a very small part of the spectrum.

Amplitude: The amount of energy in a wave Amplitude: The amount of energy in a wave. The height of the wave above or below the rest position. Wavelength: The distance between two crests (top points) or between two troughs (bottom points) in a wave. Radio waves- waves with a wavelength the size of a house. X-rays- waves with a wavelength the size of an atom. Frequency: The rate at which waves occur over time, measured in waves per second (or Hertz). 106.1 FM has a higher frequency (their waves move faster) than 94.5 FM but they are both radio waves, so their wavelengths are the same.

Stars: How do we know? The Doppler Effect explained Doppler shift – Light from moving objects will appear to have different wavelengths depending on the relative motion of the object and the observer. if the spectrum lines shift towards the red end of the visible spectrum, the star is moving away from Earth if the spectrum lines shift towards the blue end of the visible spectrum, the star is moving towards Earth The Doppler Effect explained TEACHER NOTE: The spectrum image is actually called an “absorption” spectrum. Note the black lines on the top and bottom spectrums. Comparing these to know elemental spectrums, we can analyze the makeup of a star. If, as in the top image, the dark lines are shifted to the blue side, we know the star is moving towards us. Conversely, if the dark lines are shifted towards the red, as the bottom spectrum, we know the star is moving away from us. The more the shift, the faster the star is moving. The Doppler shift was explained by Edwin Hubble. The middle spectrum is a normal light spectrum from our Sun using a triangular prism. The instrument used by scientists to gather absorption spectrum is called a spectroscope.

Doppler Shift NRAO/AUI/NSF 21

We also use the spectrum to identify elements within the universe Neon Sodium 434 nm 486 nm 656 nm Hydrogen Bottom one is hydrogen. Lines are produced as electrons jump from higher energy levels to lower ones. Energy released in the form of specific wavelengths or colors of light. NRAO/AUI/NSF 22 22

Think – pair- share How can using the spectrum to identify elements within the universe be helpful?