2 Stars: The View From Earth Constellation: a group of stars that (from Earth) resembles a recognizable formAstronomers have officially listed a total of 88 constellations – can you name any?e.g.: Ursa Major, Cassiopeia, Orion, Pegasus, Sagittarius, Ursa MinorAsterisms: smaller recognizable star patterns within a larger constellatione.g.: Big Dipper, Little DipperAstronomical phenomenon: any observable occurrence relating to astronomy
3 Stars: The View From Earth Constellations vary greatly in their distances from EarthThey appear to be twinkling because they are of similar brightness
4 Quick Lab: Reading Star Charts Use the handout to answer the following questions on your own.In which constellation is Polaris ( the North Star) located?What planet is shown in the constellation Capricornus?Betelgeuse is a large star located in what constellation?What is the name of the constellation that has three bright stars in a row?What is the name of the star that seems to form the tail of the swan-shaped constellation known as Cygnus?Is the star Aldebaran located east or west of Betelgeuse?What is the name of the star cluster located midway between the constellations of Taurus and Perseus?What large star seems to form the right foot of the constellation commonly referred to as Orion the Hunter?
5 Quick Lab: AnswersIn which constellation is Polaris ( the North Star) located?It is located in Ursa Minor or the Little Dipper.What planet is shown in the constellation Capricornus?Venus is shown in the constellation Capricornus.Betelgeuse is a large star located in what constellation?It is located in the constellation Orion.What is the name of the constellation that has three bright stars in a row?Its name is Orion.
6 Quick Lab: AnswersWhat is the name of the star that seems to form the tail of the swan-shaped constellation known as Cygnus?The name of the star is Deneb.Is the star Aldebaran located east or west of Betelgeuse?Aldebaran is located west of Betelgeuse.What is the name of the star cluster located midway between the constellations of Taurus and Perseus?The name of the star cluster is Pleiades.What large star seems to form the right foot of the constellation commonly referred to as Orion the Hunter?Rigel is the large star forming the right foot of Orion.
7 A Star Is Born Life span of stars is VERY LONG Stars are formed from a collapsing nebulaCaused by:Gravitational attraction of a nearby starShockwave from an exploding starRegion with greatest amount of matter starts to draw material towards it using gravity star forms hereStar begins to spin from energy of material coming inHigh pressures build up, heating up atoms, star glowsProtostar: star in the first stage of formation
8 A Star Is BornEventually, temperature rises to millions of degrees CelsiusNuclear reactions startsTakes thousands of years for energy from the core to reach the star’s outsideWhen this finally happens, the star begins to shine!!
9 Life Cycle of Stars100 years ago, we knew that different kinds of stars existedWe didn’t know that they had a life cycle like usHow a stars evolves in its lifetime depends on the mass it had when it was originally formedThree general mass categories:Low massMedium massHigh massDifferent masses have different lives!!
10 Low Mass Stars Use their nuclear fuel much more slowly Can last for 100 billion years8X longer than the universe’s age right now!!Less gravity and pressures than other starsShine weakly as small red stars called red dwarfsLight starts dim and gradually gets dimmerGet cooler and turns into a white dwarfThey collapse under own gravity and burn outMost stars in our universe are red dwarfs!!
11 Medium Mass Stars – Like Our Sun Burn nuclear fuel faster than red dwarfsTakes about 10 million years to use up their fuelFor those 10 million years, star is quite stableHydrogen fuel begins to run outStar collapses under own gravity like white dwarfCollapsing raises temp and pressure again in starThis causes fusion of heliumHe accumulated at the core of the starThis reignites the starBut as core heats up, stars expands quickly into a red giante.g.: AldebaranEventually, He burns out and star collapses, slowly burning out like white dwarf
12 High Mass Stars These are more than 10 times the mass of Sun Gravity makes nuclear reactions accelerateMakes star hotter, brighter, and bluerAlways will explodeHydrogen is used up in less than 7 billion yearsStar collapses like low and medium mass starsCompression causes He to fuseVERY HIGH temps cause star to expand into a supergiante.g.: Polaris, BetelgeuseWhen He fuel runs out, collapses againProcess repeats many times new elements like Fe are made
13 High Mass Stars: What an Ending!! If too much of core is made of Fe, star turns offStar collapses one final timeThe collapse is so fast and intense, star heats up to millions of degrees and EXPLODES (supernova)All elements of periodic table were made this wayExplosion sends these heavy elements to spaceCore that’s left after this goes one of two ways, depending on the mass of the original star:Neutron StarBlack Hole
14 Neutron Stars Star was between 10 and 40 times Sun’s mass Supernova’s explosion is outward and inwardAtoms at core compress and collapse, forming neutronsWhen star’s core is just a bunch of neutrons about 15 km across neutron starMade of the densest material known
15 Black Holes Star was more than 40 times Sun’s mass After supernova, star’s core is under so much gravitational force that nothing can stop its collapseNot even formation of neutronsEffect of gravity is so great that space, light, time, and other things all start to fall to a SINGLE POINTThey grow with the more stuff they pull in
17 Hertzsprung-Russell Diagram Differences between stars include:ColourBrightness or LuminositySurface Temperature1919 Ejnar Hertzsprung and Henry Norris Russell sorted and plotted thousands of stars according to these characteristicsOne of the most important discoveries in astronomy in the 20th century
18 Hertzsprung-Russell Diagram Showed very clear relationships between star propertiesColour: red on right, blue on left, yellow in betweenLuminosity: brightest at top, dimmest at bottomLuminosity of 100 means 100 times brighter than our sunSurface temp: hottest on left, coolest on right
19 Hertzsprung-Russell Diagram Patterns based on three star propertiesStar data forms a distinct band from top L to bottom RCalled the main sequence sun is a main sequence starThese stars are thought to be in stable main part of their life cycleStars not along the main sequence are often near the end of their livesWhite = hotSmall dimRed = coolLarge bright