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 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 Contains the Andromeda Galaxy – Whale Monster that was to devour Andromeda This constellation is often located beneath the horizon