The Stars, Galaxies, and Universe Light: The Astronomer’s Friend! This is what you just saw. The prism refracts (bends) the light and divides it up into its component parts. Before we can study stars, we must study the light that comes from them. For, it is this light that tells us everything that we want to know about a star. A nebula, the birthplace of stars Stars give off different types of light. We need to use these different types of light to study them. This involves using the electromagnetic spectrum. Mr. T gives off a different type of light too. What kind of light is this? Mr. T gives off a different type of light too. What kind of light is this? Visible Infrared (FLIR) Camera Camera Infrared! Visible Light is a form of electromagnetic radiation. It travels in waves, similar to the waves on the ocean. Waves have certain parts to them. The crest is the highest part, and the trough is the lowest part. The amplitude of a wave is the distance from the center of the wave to the crest (or trough). It is ½ of the wave height. Amplitude is usually measured in the base unit of meters. Wave height The wavelength of a wave is the distance from one crest to the next crest, or one trough to the next trough. The Greek letter lambda () means wavelength. The wavelength of a wave is measured in the base unit of meters. Because the waves are usually small, they are measured in μm (micrometers) or nm (nanometers). 1 μm = 1 X 10-6 m and 1 nm = 1 X 10-9 m The frequency of a wave is a measure of how many wave crests pass a certain point in a certain time. The more waves, the higher the frequency. The less waves, the lower the frequency. The Greek letter nu () means frequency The frequency of a wave is measured in units called hertz (Hz). 1 hertz = 1 cycle per second. KROQ radio broadcasts on an FM frequency of 106.7 MHz, KFWB radio broadcasts on an AM frequency of 980 KHz, and my radio control airplane works on a frequency of 72.670 MHz. Electromagnetic waves are the result of electricity and magnetism working together. The Blue arrows show the electric field and the red arrows show the magnetic field. The fields are perpendicular to each other and to the direction of the wave. Electromagnetic waves travel at the speed of light, which is measured to be 3.0 X 108 meters/second or 186,000 miles/second or 669,600,000 miles/hour? The speed of light (c) is equal to the frequency () times the wavelength (). c=x How are energy, frequency, and wavelength related? Go here to find out. Here is the calculation for radio station KROQ at 106.7 MHz, or 106,700,000 Hz = 106,700,000 cycles/second. 300,000,000 meters/second = 106,700,000 cycles/second X 2.81 meters The light that you see and the radios stations described beforehand are all part of the electromagnetic spectrum. Here is a NOVA tour of the electromagnetic spectrum. So, How do we know what stars are made of is we can’t go to them to sample their chemistry? We use a method called spectroscopy, where the spectra of a star is analyzed. We separate the light coming from a star by using a tool called a spectroscope. We then analyze the spectra, or colors, that a star emits (gives off) or absorbs. The spectra below is referred to as a continuous spectrum. Light from all visible wavelengths is being emitted. A continuous spectrum is emitted from glowing solids (a light bulb), glowing liquids (molten iron), and the hot compressed gases inside stars The second spectra below is referred to as an emission spectrum. Light from only certain wavelengths is being emitted. Each chemical element emits a different pattern of light. We can analyze these patterns to determine what chemical element(s) is(are) in a star. Go here for an example of various emission spectra for different gases. The third spectra below is referred to as an absorption spectrum. Light from only certain wavelengths is being absorbed by the cooler gas it passes through. “By comparing emission and absorption spectra, scientists can determine what elements are present in the cooler gas that is absorbing some of the light.” We can also use absorption spectra to determine the composition of a planet’s atmosphere. “If the spectrum of the reflected light from a planet contains dark lines not contained in the sun’s spectrum, then these lines must be caused by substances in the planet’s atmosphere.” Sources of Continuous, Emission, and Absorption Spectra Continuous: From a light bulb or hot metal Emission: From light emitted from a hot gas Absorption: From light that passes through a cooler gas The Doppler Effect. We can measure the amount of blue-shift or red- shift in a star’s spectrum to determine if a star is moving towards us or away from us. The Doppler Effect. You have experienced the Doppler Effect before with police cars. If the police car comes toward you, the higher pitch (shorter wavelength) you hear. The Doppler Effect. You have experienced the Doppler Effect before with police cars. If the police car moves away from you, the lower pitch (longer wavelength) you hear. The Doppler Effect. If a star is moving towards us, we will see a blue- shift. This is because the wavelengths of light are compressed into the shorter blue wavelengths. The Doppler Effect. If a star is moving away from us, we will see a red-shift. This is because the wavelengths of light are expanded into the longer red wavelengths. The Doppler Effect. The spectra of a star reveal which direction a star is moving. The Doppler Effect. A cosmological red-shift indicates that stars and galaxies are moving away from us. As Mr. Auld pointed out, this means that our Universe is expanding, or moving outwards. WOW! Stars and Their Characteristics How many stars are in our galaxy? How many galaxies are in our Universe? The stars that you see with the naked eye are only within our Milky Way Galaxy. What is the difference between astrology and astronomy? Astrology is a belief that the stars and planets can influence human life in a mystical fashion. Astronomy is a science that attempts to explain the Universe and everything within it. We are studying astronomy in this class. We call groups of stars constellations. These are names given to groups of stars by ancient astronomers. Constellations help us to find stars. Go here for more information. The Constellation Orion The positions of constellations change throughout the year because of Earth’s revolution around the sun. The Constellation Orion The Constellation Scorpius is is visible in Winter visible in Summer The Apparent Magnitude is how bright a star appears from the Earth. The lower the Star’s apparent magnitude, the brighter the star is. Negative magnitudes are the brightest stars. For each increase of 1 in apparent magnitude, relative brightness increases by 2.5 times. magnitude 0 1 2 3 4 5 6 7 8 9 10 Relative 100 4000 160 630 250 100 40 16 6.3 2.5 1 brightness 00 0 Star distances are measured in units called light years. A light year is the distance that light travels in one year. If light travels at 186,000 miles per second or 686,600,000 miles per hour, then how many miles is one light year? Star Parallax, an apparent shift in star position, is a method of measuring distances to the nearest stars. You use parallax every day. What do you use it for? Distance in parsecs = 1 / parallax angle 1 parsec = 3.26 light years 1 parsec = 3.26 light years Stars have different mass, size, and temperature. Star Type Solar masses Solar radii Sirius Main seq. 2.3 2.5 Rigel Blue super 20 36 Betelgeuse Red super 20 1,000 Aldebaran Red giant 5 20 Deneb Yellow Super 14 60 Capella Red Giant 3.5 13 Pollux Red Giant 4 8 Altair Main seq. 2 1.5 Relative Sizes of Stars Relative Sizes of Stars Relative Sizes of Stars Relative Sizes of Stars Relative Sizes of Stars Temperature and Color of Stars Temp. (C) Color Elements Class > 30,000 Bluish white Ionized He Oh 9,500-30,000 Bluish white Neutral He Be 7,000-9,500 White Metals, H A 6,000-7,000 Yellow white Metals, H Fine 5,200-6,000 Yellow Metals, H Girl (or Guy) 3,900-5,200 Yellow Metals, H Kiss orange < 3,900 red TiO2 Me The Luminosity of a star is its actual brightness. Luminosity only depends on size and temperature. The Absolute Magnitude of a star is how bright it would be if it were a distance of 10 parsecs (32.6 light years) from Earth. This is different from apparent magnitude because the apparent magnitude does not account for the distance to the star and the star’s luminosity. Apparent Magnitude vs. Absolute Magnitude Star Apparent Mag. Absolute Mag. Aldebaran +0.87 -0.65 Algol +2.09 -0.15 Antares +1.06 -5.38 Betelgeuse +0.45 -5.09 Capella +0.08 -0.48 Polaris +1.97 -3.59 Procyon +0.41 +2.62 Rigel +0.18 -6.75 Sirius -1.44 +1.42 Spica +0.98 -3.55 Cepheid Variable Stars can be used to measure long distances to stars. Cycles of brightness range from 1 to 50 days. A star with a cycle of 50 days would be brighter than a star with a brightness range of 1 day. Astronomers can calculate long distances by comparing a Cepheid’s apparent and absolute magnitude. Life Cycles of Stars are shown with a Hertzsprung-Russell Diagram Blue Super Red Super Giants Giants Main Sequence White Dwarfs Red Dwarfs We gauge the Life Cycle of Stars using the Hertzsprung Russell (H-R) Diagram Blue Super Red Super Giants Giants Main Sequence White Dwarfs Red Dwarfs Another H-R Diagram Click on this link to investigate the different life cycles of stars and how they relate to the H-R Diagram. The stability of a star depends on the balance between gravity pulling inward and energy from nuclear reactions pushing outwards. Relativity and Black Holes Albert Einstein was famous for his ideas on relativity. The Stars Study Quiz The Stars Pre Quiz Please respond with “Agree,” “Disagree,” or “Don’t Know” on a half sheet of paper. 1. We know about stars by analyzing the light that we see. 2. Stars have life cycles, which last many many years. 3. The Universe is becoming smaller. 4. Stars are much closer to us than the planets are. 5. Hotter stars are red in color.