Years of Classifying Stars Letters were assigned to stars of different spectrum. Stars were classified by the elements they were made of Stars are now classified by how hot they are and arranged by class and temperature blue 30,000 degrees + helium 10 Lacerate Blue & white 7,500 – 30000 degrees Hydrogen and helium Vega, Rigel, Sirius white Yellow 6,000 – 7, 500 degrees Hydrogen and heavier elements Procyon Yellow 5,000-6,000 degrees Calcium and other metals The sun & Capella orange 3,500-5,000 degrees Calcium and other molecules Aldebaran red Less than 3, 500 degrees molecules Betelgeuse

Types of Stars Stars are classified by how hot they are Brightest stars in the sky are called 1st magnitude Dimmest are called 6th magnitude Positive number stars are dim stars, and negative numbers represent brightest stars

Quasars A very bright (luminous) star-like object that generates energy at a high rate. Thought to be the most distant objects in the universe Some are as massive as 10 billion of our Suns Most powerful energy source in the universe

Blue Stars The hottest stars are blue stars such as Rigel, =30,000 ºC Brightest star in our night sky is Sirius

Pulsar A rapidly spinning neutron star that emits rapid pulses of radiation Develops at the end of a stars life as a last gasp before it goes “supernova”

Types of Brightness Apparent Magnitude Absolute Magnitude The brightness of a star as it is seen from Earth Our sun is very close to us so it has an apparent magnitude of -26.8 but only an absolute magnitude of +4.8 which makes it “apparently small” Absolute Magnitude The actual brightness of a star The brightness that a star would have at a distance of 32.6 light years from Earth Sun’s magnitude is +4.8

Main Sequence Stars Second and longest stage of a star’s life Energy is generated in the core of the star as hydrogen fuses to helium Size of the star remains constant as long as the core is full of hydrogen Move up and to the right on the HR diagram

Red Giant & Super giant A star that expands and cools once all of its hydrogen is gone Center of the star shrinks and its atmosphere grows Can be 10 times bigger than our sun as red giant or 100 times bigger as a super giant

White Dwarf A small hot star that is the leftover center of an older star Has no hydrogen left Final stage of a star’s life Can shine for billions of years before they cool completely

When Stars Get Old . . . Black hole Supernova an object so massive and dense that even light cannot escape its gravity Gas or dust that sink into black hole from a star form x-ray light which may indicate a black holes’ existence Supernova massive blue stars use their hydrogen quickly and may explode in a huge bright flash Can be brighter than an entire galaxy for several days A collapsed star can become a pulsar

Hertzsprung-Russell Diagram A graph that shows the relationship between a star’s surface temperature and absolute magnitude Shows how they are classified by brightness and temperature and how they change over time Hot blue stars are on the left cool red to the right, bright stars on top and dim stars on the bottom

Other Terms Spectrum – the band of color produced when white light passes through a prism Parallax – an apparent shift in the position of an object when viewed from different locations Main sequence – the location on the H-R diagram where most stars lie Neutron star – a star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons