Much of the visible matter in space makes up stars -- hot, glowing spheres of hydrogen gas that give off tremendous light energy. The billions and billions of stars vary in: The billions and billions of stars vary in: – – Size – – Density – – Temperature (colour depends on surface temp; very hot = blue; cooler = red) – – Brightness (luminosity) H-R animation H-R animation H-R animation H-R animation Star Spectra (Gizmo) Star Spectra (Gizmo) Star Spectra (Gizmo) Star Spectra (Gizmo)

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Just like organisms live, grow and die, so do stars. Gravity pulls gas and dust in a NEBULA together into a rotating sphere (composed of ~75% H and 23% He) As more material is drawn into the spinning ball, the mass at its core increases causing the temperature to rise and possibly start to glow (called a pro-star) As the process continues, heating in the core can reach o C and causes the fusion of hydrogen into helium. As a star is ‘BORN’, huge amounts of radiation are given off! A star will emit radiation for millions or billions of years!

Depending on the mass of a star it can be either a: Depending on the mass of a star it can be either a: Sun-like star or Massive star Sun-like star or Massive star They will spend most of their lives (millions to billions of years) in a stable state converting hydrogen to helium They will spend most of their lives (millions to billions of years) in a stable state converting hydrogen to helium But just like fuel in a car runs out, so will the hydrogen But just like fuel in a car runs out, so will the hydrogen So what happens when the hydrogen is used up???? So what happens when the hydrogen is used up????

When the hydrogen runs out, the stable star shrinks heating the helium core so it starts fusing to carbon, then to other elements. When the hydrogen runs out, the stable star shrinks heating the helium core so it starts fusing to carbon, then to other elements. As gravity causes the star to contract, further nuclear reactions occur, leading to the expansion of the outer layers As gravity causes the star to contract, further nuclear reactions occur, leading to the expansion of the outer layers Sun-like star  RED GIANT Sun-like star  RED GIANT – Our sun will do this in 5 billion years – It’s diameter will extend past the orbit of Mars Massive star  RED SUPERGIANT Massive star  RED SUPERGIANT

Red Giant Red Giant Red Supergiant Red Supergiant

For a Sun-like star: Fusion ends when the temp. is not hot enough to keep the reaction going Fusion ends when the temp. is not hot enough to keep the reaction going With no heat, the pressure decreases and gravity causes the star to slowly collapse on itself  WHITE DWARF With no heat, the pressure decreases and gravity causes the star to slowly collapse on itself  WHITE DWARF Eventually it will fade into a cold, dark, BLACK DWARF (it takes so long none have formed in the universe yet) Eventually it will fade into a cold, dark, BLACK DWARF (it takes so long none have formed in the universe yet) For a Massive star: Fusion ends when the fuel runs out Fusion ends when the fuel runs out With no heat input, gravity wins and the star collapses quickly and sends out a shock wave With no heat input, gravity wins and the star collapses quickly and sends out a shock wave This causes the outer part of the star to explode in a SUPERNOVA This causes the outer part of the star to explode in a SUPERNOVA If the star is not destroyed it will become a NEUTRON STAR or BLACK HOLE If the star is not destroyed it will become a NEUTRON STAR or BLACK HOLE

NEUTRON STAR NEUTRON STAR Is a rapidly spinning object only about 30km in diameter Is a rapidly spinning object only about 30km in diameter BLACK HOLE BLACK HOLE Highly dense remnant of a star in which gravity is so strong that not even light from the radiation going on inside the remnant can escape Highly dense remnant of a star in which gravity is so strong that not even light from the radiation going on inside the remnant can escape Scientists only know about them because of hoe material near them become very hot and bright Scientists only know about them because of hoe material near them become very hot and bright

What can colour and temperature tell us about the life cycle of star?

These two scientists began comparing the surface temp. of stars with its brightness. These two scientists began comparing the surface temp. of stars with its brightness. The noticed a pattern (pg. 385 Fig: 1.18): The noticed a pattern (pg. 385 Fig: 1.18): – 90% of all stars fit into their main sequence; – Our sun fits in the middle of the sequence – White dwarfs and super giants are the exception This pattern accounts for our current theory that stars evolve and change over long periods of time This pattern accounts for our current theory that stars evolve and change over long periods of time

A galaxy is a grouping of millions or billions of stars, gas and dust, held together by gravity A galaxy is a grouping of millions or billions of stars, gas and dust, held together by gravity Elliptical: a disk or football shaped galaxy made up of mostly old stars Elliptical: a disk or football shaped galaxy made up of mostly old stars Spiral: Milky Way style galaxies with long curved arms leading away from a bright central core Spiral: Milky Way style galaxies with long curved arms leading away from a bright central core Irregular: Small galaxy that lacks a definite shape Irregular: Small galaxy that lacks a definite shape

Constellations – groupings of stars we see as patterns in the night sky Constellations – groupings of stars we see as patterns in the night sky – There are 88 recognized by the International Astronomical Union (i.e. Ursa Major) Asterisms – unofficially recognized star groupings Asterisms – unofficially recognized star groupings – Big Dipper – see pg. 390 Fig. 1.23

Star clusters like Pleiades – SEVEN sisters is an asterism with an ancient myth! Star clusters like Pleiades – SEVEN sisters is an asterism with an ancient myth! Cassiopeia was a queen of Ethiopia known for her beauty. She was more beautiful than the Sea nymphs she believed. This enraged Poseidon. To punish Cassiopeia he sent Cetus the whale to destroy the coast of the Queen’s homeland! Cassiopeia was a queen of Ethiopia known for her beauty. She was more beautiful than the Sea nymphs she believed. This enraged Poseidon. To punish Cassiopeia he sent Cetus the whale to destroy the coast of the Queen’s homeland! The Nymphs sought eternal punishment, arranging for her to be placed in the heavens tied to a chair! The Nymphs sought eternal punishment, arranging for her to be placed in the heavens tied to a chair!

Our reference point for measuring the position of two objects in space is usually the Earth. Altitude and Azimuth are calculated from the observers position. Altitude is from 0° at the horizon to 90° straight up. ZENITH refers to the highest point directly overhead Azimuth determines the direction (0°= north, 90°= east, 180°= south, 270°= west) Describing the Position of Objects in Space