Stars & Universe

Absolute and Apparent Magnitudes Absolute Magnitude: is a measure of the amount of light it gives off. Apparent Magnitude: is a measure of the amount of light received on Earth. A star that’s dim can appear bright if it is close to Earth.

Measurement in Space Parallax: one way to measure the distance from Earth to stars. It is the apparent shift in the position of an object when viewed from two different positions. It can be used for relatively close stars. Light-Year: measures distances between stars and galaxies. The distance that light travels in one year. 1 light year = 9.5 trillion km/year

Properties of Stars Color indicates temperature. Hot = blue-white color Cool= orange or red The composition of stars is observed by their spectra. Each element absorbs certain wavelengths producing unique pattern of dark lines.

The Sun An average star, middle –aged, absolute magnitude is about average, yellow star, Light from the Sun takes 8 minutes to reach Earth. Main sequence star has a life span of 10 billion years. The Core: Energy produced from nuclear fusion, H atoms join to form HE Radiation Zone: Energy in the core moved out thru the radiation zone, it is a very dense areas with tightly packed gas, can take 100,000 years to move through. Convection Zone: The outermost layer of Sun’s interior, convection currents.

Sun’s Atmosphere Photosphere: Inner layer, visible light, when you see an image of the sun you are looking at the photosphere. Chromosphere: The middle layer of the sun has a reddish glow in a total eclipse. Corona: (crown) the outer layer of the sun extends into space, white halo.

Surface Features Sunspots: Dark spots due to cooler areas, shows that the Sun rotates, faster at equator (25 days) than poles (35 days), sunspot maximum occur every 10- 11 years. Prominences: Huge reddish loops of gas which link different parts of sunspot regions.

Solar Flares: Loops in sunspot, regions connect releasing large amounts of magnetic energy. The energy heats gas and erupts into space. Solar Wind/ CME: large amounts of electrically charged gas is ejected from the corona, can create powerful electric currents that cause gas to glow in the atmosphere of Earth (auroras at the poles), Can affect Earth’s magnetic field causing magnetic storms which can disrupt radio, telephone, and TV receptions.

Classifying Stars Hertzsprung and Russell developed a graph that placed temperature across the X axis and absolute magnitude on the y axis. This chart is known as the H-R diagram. The main sequence: 90 % of stars, contains hot, blue, bright stars in the upper left and cool, red, dim stars in the lower right. Yellow main sequence stars, like the Sun, fall in between. Dwarfs and Giants: 10 %, white dwarfs are small stars located on the lower left of the H-R diagram. Giants/Red giants: are large stars on the upper right of the H-R diagram, they are usually red. The largest are called supergiant.

Evolution of Stars Low-mass stars end their lives as white dwarfs and High-mass stars become neutron stars or black holes. Nebula: a large cloud of gas and dust, gravitational forces cause it to contract. It can collapse into smaller pieces and become a star. A star: the particles move closer together, temperature increases and fusion begins. The energy released radiates outward through the condensing ball of gas.

Main sequence Heat from fusion causes pressure to increase and the star becomes a main sequence. The H fuel continues to be used. The core contracts and temperatures inside the star increase. The outer layer of the star expands and cools and becomes a giant. After temperatures increase more He fuse to form C in the giant’s core. The star has gotten bigger and the outer layers are much cooler. White Dwarf: After the star’s core uses allot of He it contracts and the outer layers escape into space. What is left behind is a hot, dense core and it’s now a white dwarf. They are about the size of Earth. Eventually it will cool and stop giving light.

Supergiant and Supernova Stars that are massive (8x that of sun) stages occur quickly and violently. The core heats up to much higher temperatures. Heavier elements form by fusion and it’s a supergiant. Iron forms in the core it then and it collapses violently. The outer portion of the star explodes producing a supernova. Neutron Star: very dense stars. Black Holes: If the dense core of the supernova is more than three times massive than the sun the cores mass collapses. The gravity near this mass is so strong that nothing can escape it not even light.

Galaxies A large group of stars, gas, and dust held together by gravity. 1. Spiral: have spiral arms that wind outward from the center. The Milky Way is a spiral galaxy. 2. Elliptical: shaped like large 3-D ellipses, many are football shaped and some are round. 3. Irregular: have different shapes and are smaller than others.

The Milky Way 100,000 light-years across, contains one trillion stars, has a supermassive black hole in the center which is about 25 x more massive than the sun. Evidence comes from observing the orbit of a star near the galaxy’s center, evidence includes x-ray emissions detected by the Chandra x-ray observatory.

Expansion of the Universe The Doppler shift causes wavelengths of light coming from stars and galaxies to be compressed or stretched. As a star moves away from an observer on Earth, light from the star is shifted to the red end of the spectrum. As a star moves toward an observer on Earth, light from the star is shifted to the blue end of the spectrum.

The Big Bang Theory States that the universe began with an explosion about 13.7 billion years ago.