4.1 – 4.3

What is space like? No air – vacuum No air friction – force that resists motion Mostly black – absence of light Extreme temperatures

Galactic Shapes spiral galaxies include the Milky Way (our galaxy) all have a central nucleus have long curved arms contain a lot of gas and dust barred spirals the spiral arms are attached to a straight “bar” that runs through the center of the galaxy

Spiral Barred Spiral

Barred Spiral Galaxy

elliptical galaxies resemble an egg or a football not as structured irregular galaxies groups of stars that have no defined shapes the Large Magellanic Cloud and Small Magellanic Cloud the two closest galaxies to ours

Elliptical galaxy Irregular galaxy

Celestial Clouds nebulae large clouds of gas and dust floating in space They are most common in spiral and irregular galaxies horse head nebula is one of the most widely known nebulae

Helix Nebula Horsehead nebula

Constellations Group of stars outlining an imaginary picture most have been identified since ancient times Constellations were once used to navigate by travelers because they appear to revolve around the North Star They are also used to refer to 88 regions of the sky (celestial sphere)

North Star Polaris is the scientific name for the north star It is located directly above the Earth’s “axis of rotation” The axis is the Imaginary line that runs from the north pole to the south pole on which the Earth spins

-The oldest refers to a pattern of stars The word constellation has two current meanings -The oldest refers to a pattern of stars -The reference used by most current astronomers refers to a section of sky. -We will look at some of the patterns or arrangements of stars. The constellations seen in the Northern Hemisphere are divided into groups determined by the season in which people can see them. So we call them: Spring constellations Autumn constellations

2 groups in the northern hemisphere Spring Constellations Autumnal Constellation

Constellations of the Northern Hemisphere Ursa Major The Great Bear Contains the Big Dipper Most familiar of all constellations

Ursa Minor The Little Bear More commonly called the Little Dipper Polaris is at the point of Ursa Minor

Queen Cassiopeia Named after a mythical queen of Ethiopia Looks like a big “M” or “W” King Cepheus Looks like a house with a long pointed roof

Andromeda Mythological daughter of Cassiopeia and Cepheus Andromeda is also called “The Lady in Chains” Her head is part of the Great Square star formation Her “knee” contains the Andromeda Galaxy Whale Monster that was to devour Andromeda This constellation is often located beneath the horizon

Perseus The hero that rescues Andromeda Located above Andromeda Contains the star Algol which is a binary star A binary star is actually two stars that appear as one because they are so close

The outline of Leo’s head Pegasus The Flying Horse Leo The Lion Regulus Brightest star in the Leo constellation (probably a white dwarf) Found in the lion’s paw Sickle The outline of Leo’s head

Deneb is the brightest star in “The Swan” Cygnus or the Swan It is located on the opposite side of the Big Dipper from Leo Deneb is the brightest star in “The Swan” Deneb is also the top of the Northern Cross which is part of the Swan

Gemini The twins Castor and Pollux are the brightest stars in Gemini Castor and Pollux are the heads of the two boys Draco The dragon

Orion The Hunter Orion is the brightest of the constellations It contains two very large stars Betelgeuse Brightest star in the constellation found at the right shoulder Rigel is a blue supergiant type star If Betelgeuse was placed in the center of our solar system, it would reach past Mercury, Venus, Earth, and Mars

Canis Major Taurus The Bull Pleiades The Big Dog Large group of stars at the horn of Taurus His eye is Aldebaran (a large star) Canis Major The Big Dog Sirius is found in Canis Major and is the brightest star in the night sky

Antares is the brightest star in Scorpius There are some constellations in the Southern Hemisphere that we do not see Scorpius The scorpion Antares is the brightest star in Scorpius Antares means“Rival of Mars” The star appears red in the sky

Sagittarius The Archer It contains two other constellations The Milk Dipper The Tea Pot

Centaurus The constellation is said to resemble a creature that is half man and half horse It contains two stars that are relatively close to our sun: Alpha Centauri and Beta Centauri Alpha Centauri is the closest star to the earth other than our sun

Southern Cross It is made up of the brightest stars in the Southern Sky It is found near beneath Centaurus Many countries have this constellation in their flag