STARS AND GALAXIES The Life Cycle of a Star: Stars have a life cycle and evolve over time. The mass of a star controls its Evolution Lifespan Ultimate fate (how it dies) Our Sun: an average size star :

1.Stars begin as a nebula (cloud of gas and dust) that starts to contract due to gravity. 2. Protostar : temperature increases, millions of years later the gas becomes plasma and fusion begins. 3. Main sequence star : (the longest stage in the life of a star) nuclear fusion (hydrogen fuses into helium) continues in the core of the star...our Sun is a main sequence star. Balancing Act

Stars more massive than our Sun may be main sequence stars for only 10 million years Stars less massive than our Sun may be main sequence stars for 100’s of billions of years Remember: the larger the star the shorter the life span, the smaller the star the longer the life span

A star starts to die when hydrogen runs low: 4. Giant : A star cools as it expands and starts to glow red. Giants can be more than 10 times larger than the sun. 5. White dwarf : outer layers escape into space, the star collapses into a dense hot, dim star smaller than Earth. Path of a star much larger than our sun Path of our Sun

Massive Stars die explosively!! 4. Supergiant: Massive stars become larger than giants as they leave the main sequence….they can be 100 to 1,000 times larger than the sun. 5. Supernova: the explosion of a supergiant Neutron Star: a small dense ball of neutrons that spin after a supernova explosion Black Hole: the remnants of a supernova that are contracted even more than a neutron star… it is so dense light cannot escape from it.

Can you spot the supernova?

Are Black Holes Important? Every spiral galaxy, like our own Milky Way, is thought to have a supermassive black hole at its center. The black hole at the center of the Milky Way is sort of like the Sun at the center of our solar system - the galaxy orbits the black holes like the planets in solar systems orbit the stars. ultraviolet-light exposure

Massive Stars are important because….. During the fusion process of hotter massive stars, elements such as iron, oxygen, silicon and magnesium are created. These are elements needed for life. Composition of Universe

Two types of brightness: absolute magnitude and apparent magnitude Apparent magnitude is the brightness we see here on Earth Absolute magnitude is the actual brightness the star gives off. The more negative the number, the brighter the star is! Magnitude describes the brightness of a star

ORION CONSTELLATION Betelgeuse Rigel

To figure out how far it is to a star, astronomers look at it from two different positions, called parallax Parallax is a method used to determine distance to a star.

Not all stars are the same color because different elements burn different colors. Some are red, some are blue, etc. Color tells the temperature of the star Hot stars are bluish/white and cooler stars are reddish/orange Astronomers call this a star’s spectral class. Spectral classes are O, B, A, F, G, K, and M STARS ARE CLASSIFIED BY THEIR SIZE, COLOR AND TEMPERATURE Flame Test Clip

O, B, A, F, G, K, and M... (Oh Be A Fine Guy Kiss Me) and for you guys: Oh Be A Fine Girl Kiss Me!!

Hertzsprung-Russell Diagram (H-R Diagram) Stars are ranked on the H-R Diagram based on their temperature and absolute magnitude Most stars fall in the middle of the diagram, called the main sequence Very few stars are white dwarfs or giants/supergiants

H-R Diagram---shows the life cycle of stars temperature Absolute magnitude Main sequence supergiants giants White dwarfs

THE 3 TYPES OF GALAXIES Our galaxy, the Milky Way is part of a larger group of galaxies called the Local Group There are about 30 galaxies included in the Local Group The Andromeda galaxy is an example of a spiral galaxy with huge spiral arms. Astronomers believe the Milky Way resembles this. There are three types: elliptical, spiral, and irregular 1.Our galaxy the Milky Way is a spiral galaxy

2. Elliptical galaxies are the most common Elliptical can be football-shaped Irregular 3. Irregular are all the galaxies that are NOT spiral or elliptical, and are not nearly as common

Where Are We in Our Galaxy?

AMAZING EARTH SCIENCE FACTS The life cycle of our sun is _________, ___________________, ___________, and finally a ______________________. _____________are a death stage of massive stars We are located in the ___________Galaxy which is a _______ galaxy The 3 types of galaxies are________, ___________, and _____________ The Sun is located about ______________between the center of the galaxy and an outer spiral arm nebula main sequence red giantwhite dwarf Black holes Milky Way spiral elliptical irregular midways

Constellations Constellations are patterns of stars in the night sky, commonly named after animals and characters in Greek mythology Currently there are 88 that are named If you look in the direction of north, there are constellations that appear to move in a circle around the North Star, Polaris. These are circumpolar constellations. They are visible year-round in each hemisphere