The Wonder And Beauty Of: stars

Stars: The View From Earth Constellation: a group of stars that (from Earth) resembles a recognizable form Astronomers have officially listed a total of 88 constellations – can you name any? e.g.: Ursa Major, Cassiopeia, Orion, Pegasus, Sagittarius, Ursa Minor Asterisms: smaller recognizable star patterns within a larger constellation e.g.: Big Dipper, Little Dipper Astronomical phenomenon: any observable occurrence relating to astronomy

Stars: The View From Earth Constellations vary greatly in their distances from Earth They appear to be twinkling because they are of similar brightness

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?

Quick Lab: Answers In 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.

Quick Lab: Answers What 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.

A Star Is Born Life span of stars is VERY LONG Stars are formed from a collapsing nebula Caused by: Gravitational attraction of a nearby star Shockwave from an exploding star Region with greatest amount of matter starts to draw material towards it using gravity  star forms here Star begins to spin from energy of material coming in High pressures build up, heating up atoms, star glows Protostar: star in the first stage of formation

A Star Is Born Eventually, temperature rises to millions of degrees Celsius Nuclear reactions starts Takes thousands of years for energy from the core to reach the star’s outside When this finally happens, the star begins to shine!!

Life Cycle of Stars 100 years ago, we knew that different kinds of stars existed We didn’t know that they had a life cycle like us How a stars evolves in its lifetime depends on the mass it had when it was originally formed Three general mass categories: Low mass Medium mass High mass Different masses have different lives!!

Low Mass Stars Use their nuclear fuel much more slowly Can last for 100 billion years 8X longer than the universe’s age right now!! Less gravity and pressures than other stars Shine weakly as small red stars called red dwarfs Light starts dim and gradually gets dimmer Get cooler and turns into a white dwarf They collapse under own gravity and burn out Most stars in our universe are red dwarfs!!

Medium Mass Stars – Like Our Sun Burn nuclear fuel faster than red dwarfs Takes about 10 million years to use up their fuel For those 10 million years, star is quite stable Hydrogen fuel begins to run out Star collapses under own gravity like white dwarf Collapsing raises temp and pressure again in star This causes fusion of helium He accumulated at the core of the star This reignites the star But as core heats up, stars expands quickly into a red giant e.g.: Aldebaran Eventually, He burns out and star collapses, slowly burning out like white dwarf

High Mass Stars These are more than 10 times the mass of Sun Gravity makes nuclear reactions accelerate Makes star hotter, brighter, and bluer Always will explode Hydrogen is used up in less than 7 billion years Star collapses like low and medium mass stars Compression causes He to fuse VERY HIGH temps cause star to expand into a supergiant e.g.: Polaris, Betelgeuse When He fuel runs out, collapses again Process repeats many times  new elements like Fe are made

High Mass Stars: What an Ending!! If too much of core is made of Fe, star turns off Star collapses one final time The collapse is so fast and intense, star heats up to millions of degrees and EXPLODES (supernova) All elements of periodic table were made this way Explosion sends these heavy elements to space Core that’s left after this goes one of two ways, depending on the mass of the original star: Neutron Star Black Hole

Neutron Stars Star was between 10 and 40 times Sun’s mass Supernova’s explosion is outward and inward Atoms at core compress and collapse, forming neutrons When star’s core is just a bunch of neutrons about 15 km across  neutron star Made of the densest material known

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 collapse Not even formation of neutrons Effect of gravity is so great that space, light, time, and other things all start to fall to a SINGLE POINT They grow with the more stuff they pull in

Life Cycles of Stars

Hertzsprung-Russell Diagram Differences between stars include: Colour Brightness or Luminosity Surface Temperature 1919 Ejnar Hertzsprung and Henry Norris Russell sorted and plotted thousands of stars according to these characteristics One of the most important discoveries in astronomy in the 20th century

Hertzsprung-Russell Diagram Showed very clear relationships between star properties Colour: red on right, blue on left, yellow in between Luminosity: brightest at top, dimmest at bottom Luminosity of 100 means 100 times brighter than our sun Surface temp: hottest on left, coolest on right

Hertzsprung-Russell Diagram Patterns based on three star properties Star data forms a distinct band from top L to bottom R Called the main sequence  sun is a main sequence star These stars are thought to be in stable main part of their life cycle Stars not along the main sequence are often near the end of their lives White = hot Small  dim Red = cool Large  bright