Stars & Galaxies By Gina Wike

Constellations A constellation is a group of stars that when viewed from Earth look close together. In most cases, they are not related to one another.

Betelguese Betelguese is in the right shoulder of the constellation Orion.

Sirius The brightest star in the winter sky is Sirius and is located in Canis Major.

Big Dipper The Big Dipper is part of Ursa Major.

Polaris Polaris is the North Star and is located in the end of the Little Dipper- Ursa Minor.

Circumpolar Constellations Circumpolar constellations circle around Polaris in the northern sky. All of the constellations appear to move because Earth is moving.

Constellations The constellations also appear to change positions in the sky because the Earth revolves around the sun. For example, Orion is visible in the winter sky, but not in the summer.

Apparent & Absolute Magnitude The absolute magnitude of a star is a measure of the amount of light a star actually gives off. The amount of light received on Earth is apparent magnitude. A star that is actually dim can appear very bright if it is close to earth. The opposite is true also. A star that’s actually bright can appear dim if it is far away.

Parallax Parallax is the apparent shift in the position of an object when viewed from two different locations.

Parallax Observation: hold your hand at arm’s length and look at one finger first with your left eye and then with your right eye. Your finger appears to change position. Try the same thing with your finger up closer to your face. What do you notice? The nearer an object is to the observer, the greater its parallax. Parallax can be used to measure distance from Earth of relatively close stars.

Light Years Distances in space are measured in light- years. A light-year is the distance light travels in one year. Light travels at 300,000 km/s or about 9.5 trillion km in a year.

Light Years The nearest star to the Earth is Proxima Centauri and is 4.2 light years away; it takes 4.2 years for the light to reach your eyes. It is part of a group of stars known as Alpha Centauri

Star Color The color of a star determines its temperature. Very hot stars are blue-white. Cool stars are orange or red. Our sun is yellow.

Spectrographs Astronomers use spectrographs to study the spectra of stars to identify properties of stars. Spectrographs break visible light into its component colors.

Star Spectra Dark lines are in the spectrum of a star. The dark lines are caused by elements in the star’s atmosphere.

Spectra As light passes through a star’s atmosphere, some of it is absorbed by elements in the atmosphere and appear as black lines in the spectrum. Each element has a certain pattern of black lines and can be used to identify which elements are in a star.

H-R Diagram Hetzsprung and Russell noticed that for most stars, the higher their temperatures, the brighter their absolute magnitudes. They developed the H-R diagram. The temperatures were placed across the bottom and the absolute magnitude up the side. Most stars fit into a diagonal band that runs from the upper left to the lower right. This band is called the main sequence.

H-R Diagram

Star Evolution 90% of all stars are main sequence stars. The sun is a main sequence star.

Fusion Stars produce energy by fusing hydrogen into helium. 4 hydrogens combine to form one helium; mass is lost in the reaction. Fusion occurs in the cores of stars

Star Evolution The mass of a star determines its life cycle.

Star Evolution A star begins as a cloud of gas and dust known as a nebula.

Star Evolution Nebula contracts, temperatures increase, and fusion begins; a star is born. The star becomes a main sequence star. A main sequence star fuses hydrogen into helium until it is used up.

Star Evolution There is no longer a balance between pressure and gravity, so the core contracts, temperatures increase, causing the outer layer of the star to expand forming a giant. Helium fuses to form carbon in the core.

Star Evolution The core contracts and then uses up the carbon. When the core runs out of fuel, the outer layers escape into space and only the hot, dense core remains. The core contracts even more under the pressure of gravity and becomes a white dwarf.

Star Evolution In stars 10 times greater than the sun, the star becomes a supergiant. Eventually iron forms in the core and fusion cannot take place.

Star Evolution The core collapses and the outer portion of the star explodes, producing a supernova. A supernova can be millions of times greater than the original star. The collapsed core shrinks so that only neutrons can exist in the dense core. It becomes a neutron star.

Star Evolution If the remaining dense core is 3 times larger than the sun, it will quickly become a black hole. A black hole is so dense that nothing can escape its gravity field. Black holes give off x-rays.

Sun-main sequence Rigel-Supergiant Aldebaran-Red Giant Betelgeuse & Antares-Supergiant

Star Evolution Nebula comes from matter that was once in stars. Stars eject lots of matter during their lifetime. The matter in stars is recycled many times.

Sun Our sun has iron and carbon according to its spectrum; it is too young to have produced it, so it must have come from stars that died billions of years ago.

Elements in the Universe Some elements condense to form planets instead of stars. Our bodies contain elements that were fused in the cores of ancient stars. Most scientists believe the early universe consisted only of hydrogen and helium. More than 99% of the matter in our solar system is in the sun.

Sun Our sun is an average star. The sun is a main sequence star. The sun is a giant ball of gas fusing hydrogen into helium.

Sun Atmosphere The photosphere is the lower layer of the atmosphere that gives off light. The chromosphere is above the photosphere. Above the chromosphere is the corona.

Corona & Solar Winds The corona is the largest layer of the sun’s atmosphere.

Solar Winds Charged particles are given off by the corona and move through space as solar winds.

Sunspots Sunspots are the dark areas that are cooler than other areas on the sun. By studying the position of sunspots, we learned the sun rotates. The sun rotates faster at the equator than the poles. Sunspots are not permanent features on the sun. Sunspot maximums occur every 11 years. The last maximum was in The next maximum will be in 2012.

Prominences Prominences are huge arching columns of gases

Prominences It is believed they are caused by the intense magnetic field associated with sunspots.

Solar Flares Gases near sunspots sometimes shoot out at high speeds, These violent eruptions are solar flares. Solar flares increase aurora activity in both hemispheres.

Auroras Aurora Borealis- northern hemisphere; Aurora Australis- southern hemisphere Alaska-Aurora Borealis Aurora Australis

Aurora Borealis

Maine

Aurora Australis

Sun Most stars are in systems where 2 or more stars orbit one another. This is a binary system. Our sun is not in a binary system.

Galaxies A galaxy is a large group of stars, gas, and dust held together by gravity. Galaxies are grouped together in clusters. Our cluster is the Local Group. There are 3 types of galaxies: elliptical, spiral, and irregular.

Milky Way Galaxy Our galaxy is the Milky Way Galaxy and contains about 200 billion stars.

Spiral Galaxies Spiral galaxies have spiral arms that wind out from the center. The spirals are made up of stars and dust. There are fewer stars between the arms.

Barred spirals have 2 arms that extend from a large bar that goes through the center of the galaxy.

Milky Way The Milky Way is probably a normal spiral galaxy. Recent evidence points to it being a barred spiral. We can’t tell because we are in one of the arms and cannot look at it from the outside.

Milky Way The sun is located on the left side of the center of the galaxy. The Milky Way is 100,000 light years across.

Doppler Shift A Doppler Shift occurs with light and sound. When a car blows its horn as it passes by, it has a high pitch and gets lower as it goes by. This is a Doppler Shift in sound.

In light, a redshift in spectrum indicates that a galaxy is moving away from you and a blueshift means that a galaxy is moving toward you.

Redshift Because all galaxies beyond the Local Group show a redshift, it means that the galaxies are moving away from us. This means that the universe is expanding.

Big Bang Theory The big bang theory is the theory for the formation of the universe. The theory states that 15 to 20 billion years ago, the universe began expanding out of an enormous explosion. Scientists have discovered radiation in space they believe was created by the Big Bang.