Chapter 10: Stars

What is a star? The objects that heat and light the planets in a system A star is a ball of super hot gas (plasma) held together by its own gravity Nuclear reactions occur in stars (nuclear fusion of hydrogen gases to helium; H  He)

I. Stars The Brightness of Stars -Star: A hot glowing sphere of gas that produces energy by fusion. -Fusion: The joining of separate nuclei. Common in nature, but not on Earth.

Characteristics of Stars Magnitude (brightness) A measure of brightness of stars Apparent magnitude How bright a star appears to be from Earth Absolute magnitude How bright a star actually is

Brightness The brightness of a star is dependent size temperature and distance from Earth. Apparent Brightness – is the brightness of a star as it appears from Earth. The apparent brightness decreases as its distance from you increases Absolute Brightness – is how bright a star really is. The absolute brightness is a characteristic of the star and is not dependent on its distance from Earth.

1. Actual vs. Apparent Brightness Variables which affect a star’s brightness: Star size Distance from Earth Star temperature Apparent Brightness: The amount of light received on Earth from a star. Actual Brightness: How large and hot a star is in relation to other stars.

Star Brightness Example: Sirius has a greater apparent brightness then Rigel, even though Rigel is a much hotter and brighter star. Why?

Characteristics of Stars Temperature & Color The color of a star indicates the surface temperature of the star Below is the colors from hottest to coolest

Properties of Stars Astronomers classify stars by their color, size, and brightness. Other properties of stars are chemical composition and mass. Color and Temperature – a stars color indicates the temperature of its’ surface. The hottest stars appear blue The cooler stars appear red The spectrum of color in a star is from blues to greens to yellows and reds.

Determining a Star’s Temperature A star’s temperature can be determined by its color. All objects will glow a different color when heated differently Colors hottest to coolest: Blue/white  yellow  orange  red.

Star Size Dwarfs- small and mediums sized stars The Sun is actually a medium sized star, it is just very close Giant Stars- 10’s-100’s of times larger than dwarfs, and 100’s of times brighter Supergiants- the biggest and brightest of the stars Thousands of times brighter and hundreds of times bigger

Characteristics of Stars DISTANCE Measured in light-years The distance which a ray of light would travel in one year About 6,000,000,000,000 (6 trillion) miles 186,000 miles per second

Light-Years Light-year: Distance light travels in one year. (Equal to about 9.5 trillion kilometers) Approximate distances: -Sun to edge of solar system = 5.5 light hours -Nearest star (Alpha Centauri) = 4.3 light years -Center to edge of Milky Way = 50,000 light years

Parallax Astronomers have developed various methods of determining the distance of stars. The change in position of a star in relationship to other stars is called parallax. As Earth moves in its orbit, astronomers are able to observe stars from two different positions. Astronomers measure the parallax of nearby stars to determine their distance from Earth

Kinds of Stars Variable Stars A variable star is a star that regularly or repeatedly changes in magnitude Pulsating variable star- has periods of swelling and shrinking Eclipsing Variable Stars- occurs when pairs of stars orbit each other because of their gravitational pulls on each other

Pulsating Variable Stars

Variable Stars Eclipsing Variable Stars

Kinds of Stars: Novas A nova is a new star It is believed they form when an existing star suddenly flares up and becomes hundreds or thousands of times brighter

How Stars Form A nebula is a large cloud of gas and dust spread out over a large volume of space. Some nebulas are glowing clouds lit from within by bright stars. A star is formed when a contacting cloud of gas and dust becomes so dense and hot that nuclear fusion begins.

Kinds of Stars Nebula: A large cloud of interstellar gas and debris. Dust and gas particles exert a gravitational force on each other which keeps pulling them closer together. Orion Nebula

More Nebulas As the particles pull closer together the temperature increases. Another view of Orion

Kinds of Stars When no more hydrogen is left in the core it explodes into a supernova. This is the death explosion of a star The star grows bigger and brighter and finally collapses

Kinds of Stars: Supernovas Smaller stars become neutron stars Pulsar: a neutron star that spins rapidly on its axis Massive supernovas will collapse into a black hole. Neutron Star

Life Cycle of Stars Life span of a star depends on its size. Very large, massive stars burn their fuel much faster than smaller stars Their main sequence may last only a few hundred thousand years Smaller stars will live on for billions of years because they burn their fuel much more slowly Eventually, the star's fuel will begin to run out.

The Death of a Star The dwindling supply of fuel in a star’s core leads to the star’s death as a white dwarf, neutron star, or black hole.

Nothing (even light) can escape the gravity of a BLACK HOLE

Life Cycle of Stars

Life Cycle of Stars

Life Cycle of Stars If the star is massive enough, the collapse will trigger a violent explosion known as a supernova If the remaining mass of the star is about 1.4 times that of our Sun, the core is unable to support itself and it will collapse further to become a neutron star

Constellations Constellations are groups of stars in patterns (animals, heroes… etc) Stars that appear to revolve around the North Star are called circumpolar constellations

Astrology Astrology is the study of how the stars and cosmos control or guide our lives A type of religion for some Astronomy is the scientific study of stars How they form Where they are located Their size and composition

Telescopes Refracting telescope- bend, or refract, light to make objects seem larger Reflecting telescopes- produce a clearer image because the light is not bent, but rather reflected through a series of mirrors Radio telescopes- collect radio waves (using a concave disk) to detect objects other telescopes cannot

Spectroscopes They break down light given off a star into all of its colors

Spectroscope Redshift occurs when an object moves away from the Earth the wavelengths become longer, causing the colors shift towards the red end of the color spectrum

Star Groups: Small Groups Binary System is the smallest of star groups It consists of 2 stars close together Multiple Star Groups consists of three or four stars that stay close together

Star Clusters Open Star Clusters a group of several hundred to a few thousand stars with no particular arrangement Globular Cluster is a group of several thousand to a million stars arranged in a ball shape

Galaxies A galaxy is a huge star system that has millions to billions of stars and covers many light years of space We live in the MILKY WAY

The Milky Way Galaxy 100,000 light years in diameter Our sun orbits the center of the galaxy once every 240 million years Contains over 200 billion stars Its where I live!!!!!

The Local Group Local groups are galaxies close to galactic neighbors The Milky Way and Andromeda are in the local group

Space Objects Asteroids- irregularly shaped pieces of rock, metal, and dust Meteoroids- a chunk of metal or stone that is moving towards the Earth Meteor- a meteoroid that has moved through Earth’s atmosphere and light’s up Meteorites- meteors that hit the Earth’s surface

Space Objects Comets are chunks of frozen gases, water and dust that orbits the Sun over and over again