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

Actual vs. Apparent Brightness Variables which affect a star’s brightness: 1.________________ 2.________________ 3.________________ _______________: The amount of light received on Earth from a star. ______________: How large and hot a star is in relation to other stars.

Star Brightness Example: (Fig. 20.1) Sirius has a greater apparent brightness then Rigel, even though Rigel is a much hotter and brighter star. Why?

B. The Birth of a Star Stars form in dark, cool clouds called ____________. Something happens to make these clouds __________and __________. Orion Nebula

More Nebulas ________ pulls all of the pieces close to the center and squeezes them creating immense pressure. This contraction could last over a __________years. Another view of Orion

Protostar Stage The temperature of this gaseous body continues to rise until it starts emitting _____________, like the burner of a stove. Stars that are red have the _________surface temperature and the _____________ wavelength light. The inside of the protostar continues to increase in temperature. When it reaches about _____________degree s Fahrenheit, __________________ __________________ begins and a star is born.

Main-Sequence Stage Stars have an enormous amount of __________inside of them that pushes them out. ____________ holds this pressure back and keeps the star together. It is this balance between pressure and gravity that forms a _______________star.

Main Sequence Cont. Different stars ______at different rates. ______________ produce a large amount of short wavelength, high energy ______light. These stars _________their fuel very quickly and burn out within a few million years. A ____________like our Sun, burns its’ fuel much ________ and lasts about _____ billion years. _______________ that burn _______and produce ________wavelength, low energy ______light can last for ____________________

Red Giant Stage As a star gets _______, the __________fusion slows in the core and moves out toward the outer part of the star. When this happens, the _________core ________, becomes very hot and increases the hydrogen fusion on the outer part of the star. This makes the star grow 100’s or 1,000’s of times its normal size. Eventually the giant uses all of its’ Hydrogen and Helium fuel and ______under the force of ________.

Burnout and Death There are many ways that a star can die. The way in which this happens depends on the stars’ __________.

A) Low Mass Stars A low mass star never burns the helium in its’ core, so it never becomes a _________. Low mass stars _______under the force of _______and form ____________.

B) Medium Mass Stars Planetary Nebula Medium mass stars become __________and fuse helium and hydrogen at a fast rate. Medium mass stars shrink to _______too, but before they do, they eject their outer layer of gas. This is called a ____________

C) Massive Stars Massive stars become ___________. They are very large when they finish consuming their hydrogen and helium. They collapse with such force that they explode, producing a _____________. The intensity of a massive star collapsing produces a super- dense star called a ___________. Imagine a star 1,000,000 times bigger than our sun becoming a star that is 20 km across. This would be like taking the Earth (8,000 miles across) and squeezing it down to 100 yards across. One pea sized sample of a neutron star weighs over 100 million tons. In some rare cases, the red supergiant is so massive that when it collapses it produces a ____________

Black Hole Neutron Star

Black Holes Black holes should be very hot. Usually hot things glow brightly, like a star. However, the gravity pulling the surface of a black hole toward the center is so strong that not even light can escape from its’ surface, so they completely disappear from sight. Anything that gets too near to a black hole is swept in by its’ gravity and lost forever.

Study of Stars ­Scientist study stars by using the Hertsprung Russell Diagram. The HR Diagram compares a stars ___________with its’ _________________

Hertsprung-Russell Diagram

Determining a Star’s Temperature A star’s temperature can be determined by its ________. All objects will glow a different color when heated differently Colors hottest to coolest: _________  _________  ______  _________.

Determining a Star’s Composition Starlight is separated into a spectrum with a _________________ A star’s light has dark bands along the spectrum, these bands are caused by the absorption of certain wavelengths of light by specific gases in the star. Different bands show what elements are in the star’s atmosphere.

A star’s spectrum

Light-Years ____________: 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

The Sun and You Our sun is a main sequence star according to the H-R Diagram. The actual brightness is average for a star of its average size.

Layers of the Sun Dense inner _____which is the site of hydrogen fusion. ____________: Energy bounces back and forth before escaping. ____________: Cooler layer of gas that is constantly rising and sinking.

Anatomy of Sun Photosphere: Bright source of much of the light we see. Chromosphere: Active layer which is home to many significant displays.

Anatomy of Sun _________: Outer layer which is a gradual boundary between sun and space.

Sunspots __________: Cool dark areas on the sun’s surface. -First discovered by Galileo -Not permanent features—Will appear and disappear

Cycle of Solar Activity Cycle of Solar Activity: 11 year cycle which see number of sunspots change. Sunspot Maximum: Time of many large sunspots. Sunspot Minimum: Time of few sunspots.

Prominences and Flares Prominence: A huge arching column of gas.

Prominences and Flares _____________: Violent eruptions near a sunspot which suddenly brighten and shoot outward at high speed.

Prominences and Flares The interaction of solar flares with Earth’s magnetic field causes the aurora borealis/ aurora australis (Northern/Southern Lights)