stellar nursery in the the A young is being born in the center of a pillar of dust and gas in the , an intensely active region of stellar formation 7,500 light- Galactic center years from . The nebula’s giant range Earth’s Galactic Home NGC 5272 up to a hundred times more massive than the . The biggest of them, , will soon ex- Earth’s orbit around the sun lies at a plode in a , blasting matter into space Earth’s location on the outskirts of the Milky Way means we view the great spiral EARTH Ecliptic severe angle to the galactic plane. and providing seed material for new stars. from the side, and its 200 billion or more stars look like a glowing band SUN plane across the sky. This is the galactic equator—the plane on which the solar system Galactic orbits the center of the Milky Way every 220 million years. If the pace sounds plane slow, Earth careens on this cosmic merry-go-round at about 917,000 kilome- ters an hour (570,000 mph). The galaxy has three distinct parts: At the core is a 330° bright, bar-shaped bulge of yellow and red stars. From the center, several spiral 300° arms sweep out to form a disk that contains younger, blue stars, as well as glowing regions of star birth. Earth resides here, 25,000 light-years from the center, and 0° most of the familiar celestial spectacles—supernovae, planetary nebulae, star birth M14 regions—lie relatively nearby. Finally, surrounding the galactic disk is a great halo M80 270° of dark matter—invisible, but holding most of the galaxy’s .

Globular Far beyond the galactic disk, yet drawn by clusters Halo its , lone stars and globular clusters 30° wander the galaxy’s halo. Regions of dark Disk matter—unseen but felt through its gravita- D ar tional effects—extend beyond that. k m

atter

Omega Centauri

NGC 5139 M 240° M

R

M M R R R A

A A

A C C

P P S

K K

U 3 3 S 60° M92 R R R M A U A E R U Globular F N I 10 A A ,00 0 Interstellar gas and dust A T R M N R E A Nebula O C N - T Younger star region M M71 U T T I M4 U S C G Galactic bulge or center 20 Kappa Crucis A ,00 NGC 4755 (older star region) 0 Butterfly S NGC 6302 Carina NGC 3372 Reference numbers for , S NGC 6397 Keyhole NGC 3324 nebulae, and star clusters Eagle M16 A IC (Index Catalogue) Omega M17 Lagoon M8 OUR SOLAR SYSTEM G Wild Duck M (Messier) P M10 NGC () I M11 Owl M97 Vela T M12 M2-9 Trifid M20 Antares E T Ring M57 Coordinate system centered A R Dumbbell M7 on galactic center I U M27 NGC 7293 Orion 210° 3 S A R M R 0, M42 00 NGC 7027 Cone NGC 2264 0 North America NGC 7000 Rosette NGC 2237 R S O U 90° R I O N S P E 3,000 U S Crab M1 ears A IC 1848 6,000 light-y R Soul Nebula M SN 1572 Tycho’s Supernova 4 0, 00 0

5 0 ,0 Celestial Wings take Flight 0 0

l Delicate “wings” of superhot gas that once ig h t - D formed the outer layers of a star five times as y i e re a c r t massive as the sun span trillions of miles of s io n o space in the beautiful Butterfly Nebula, also f ro t known as the Bug Nebula. The gas is swept at io n 120° outwards at nearly 965,000 kilometers an hour (600,000 mph) by wind blowing from the dy- ing star at the center of this about 2,000 light-years from Earth. O M R brahe’s “stella noVa” This star explosion some 7,500 light- U A “On the 11th day of November in the years from Earth disproved the traditional T E R notion that the heavens were unchanging, evening after sunset . . . I noticed that 180° a new and unusual star, surpassing the and revealed them as highly dynamic. The Palomar I other stars in brilliancy, was shining faded remnant is now a colorful planetary almost directly above my head.” So wrote nebula, shown here in an image combin- 150° Danish Tycho Brahe of the ing and x-ray orbital telescope supernova that burned briefly in 1572. views with ground-based optical imagery.

CroWded stellar neighborhood Maximum stars crowd a minimum of space in the . Upgrades to the heart oF the Milky Way in 2009 revealed previously unseen color The mysterious core of our galaxy is detail, providing clues to the life cycles of revealed in greater detail than ever the cluster’s ten million stars: Those at before in this dazzling mosaic of midlife are yellow-white, while older ones hundreds of thousands of individual are orange, and red giants are nearing images from the infrared Spitzer Space the end. Separated by just one-third of a Telescope. New stars are coalescing in light-year on average, collisions can occur. bright regions of yellow and red, while By contrast, the sun’s closest neighbor is the green haze is gas thrown off from over four light-years distant. Though Omega star birth. Blue pinpricks throughout the Centauri is unusually large, the Milky Way’s image are the Milky Way’s older stars. halo contains many such globular clusters— What the image can’t show is Sagittarius dense spherical star clouds that orbit the A*, a supermassive whose galactic center like miniature galaxies. gravity dominates the Milky Way’s core. 118 118

118 Milky Way FFR.indd 118-119 6/30/10 2:02 PM