Chap. 24-1 Notes: Stars

Constellations

What are Constellations? An apparent pattern of stars seen by viewers that seems to travel together across the night sky. * named after animals, mythological characters, or familiar objects.

Early Greek astronomers named many of the constellations.

Orion – The hunter

Orion

Orionids meteor shower (Oct. 20)

Taurus – The Bull

They are not really groups of stars! In most cases the stars in a constellation are not actually together in space!

Modern astronomers have divided the sky into 88 constellations.

Circumpolar Constellations Constellations that trace daily circles around the North Star(POLARIS). They never move below the horizon. Move in counterclockwise direction. Visible year-round.

Florida’s Circumpolar View Most of U.S. Florida’s View

Five Circumpolar Constellations Ursa Major, the Big Bear (includes the Big Dipper) Ursa Minor, the Little Bear Cassiopeia, the Queen of Ethiopia Cepheus, the King of Ethiopia Draco, the Dragon

Asterisms Asterism -A small group of stars that forms a visible pattern but is not an official constellation. Examples: Big Dipper Summer Triangle Orion's Belt Summer Triangle

Ursa Major – The Great Bear A circumpolar constellation. Contains an asterism called the “big dipper” Pointer stars shows north star! (Polaris)

Star Brightness

Magnitude Refers to the brightness of a star.

3 factors affect a stars brightness 1) Temperature 2) Size 3) Distance from Earth

Apparent Brightness (apparent magnitude) How much light we receive from the star.

Absolute Brightness (absolute magnitude) How much light the star is actually giving off.

Distance vs Brightness Two stars of equal size and temp. but at different distances… the furthest is the dimmest.

Temp. vs. Brightness

Size vs. Brightness

Sometimes a small, HOT star is just as bright as a large, COOL star.

Light-Year (ly) The DISTANCE that light travels in one year. * used to measure distance to stars & galaxies. * Light travels 300,000 Km/sec or about 9.5 trillion Kilometers in a year

Polaris (the North Star) The light we currently see from the North Star was actually emitted in the year 1583.

Proxima Centauri * about 4.2 light-years away The closest star to the Earth after the Sun. * about 4.2 light-years away

Thought to be part of a triple-star system. Proxima Centuri is a red dwarf star. Thought to be part of a triple-star system.

Parallax The apparent shift in the position of an object when viewed from two different positions. * a method used to measure the distance to a star

Parallax – good for nearby stars.

Ways that Stars vary: 1. size 2.composition 3.Temperature 4.color 5. mass 6.brightness.

Differences in temperature of stars determined by it’s color. * Blue or Blue-white 35,000 oC * White 10,000 oC * Yellow 6,000 oC * Red-orange 5,000 oC * Red 3,000 oC * Brown 1,000 oC

Size Differences

Sizes of Stars List is from largest to smallest diameter. Super Giant Giant Medium Dwarf Neutron

What are Stars Made of? The composition of a star is determined by studying its spectrum. Instrument = Spectrograph (prism)

A star’s spectrum is like a fingerprint No two stars have the same spectrum!

Common Elements of a Star Hydrogen - 72% Helium - 27% Oxygen - <1% Carbon - <1% Iron - <1% Neon - <1% Magnesum - <1% Nitrogen - <1%

The End