Al Bustan 


IC5146 - Cocoon
M5 - NGC5904
M8 - Lagoon Nebula
M16 - Eagle Nebula
M20 - Trifid
M27 - Dumbbell
M31 - Andromeda
M33 - Pinwheel
M42 - Orion
M45 - The Pleiades
M51 - Whirlpool
M57 - Ring
M63 - Sunflower
M64 - Black-Eye
M65 - NGC3623
M67 - NGC2682
M98 - NGC4192
M99 - Pinwheel
M100 - NGC4321
M101 - NGC5457
M104 - Sombrero
M105 - NGC3379
M106 - NGC4258
C/2004 Q2 - Machholz
NGC 891
NGC2024 - Flame
NGC2244 - Rosette
NGC6960 - Veil
The Mice - NGC4676






The galaxy M100 is one of the brightest members of the Coma-Virgo Cluster of galaxies of an estimated 2,500 galaxies, at 50 to 60 million light years away (see bottom text)). The galaxy is in the spring constellation Coma Berenices and can be seen through a moderate-sized amateur telescope. M100 is spiral shaped, like our Milky Way, and tilted nearly face-on as seen from Earth. The galaxy has two prominent arms of bright stars and several fainter arms. The galaxy does not yield its spiral form easily. Faint dwarf galaxies are just to the north and east of this coiled galaxy. To the north, NGC 4322 is a probable companion, but NGC4328 to the east appears to be in the foreground.





This NASA Hubble Space Telescope image of a region of the galaxy M100 shows a class of pulsating star called a Cepheid Variable. Though rare, these stars are reliable distance indicators to galaxies. Based on the Hubble observation, the distance to M100 has been measured accurately as 56 million light-years (+/- 6 million light-years), making it the farthest object where intergalactic distances have been determined precisely. Hubble's high resolution pinpoints a Cepheid, which is located in a starbirth region in one of the galaxy's spiral arms (bottom frame). The top three frames were taken on (from left to right) May 9, May 4, May 31 1994, and they reveal that the star (in center of each box) changes brightness. Cepheids go through these changes rhythmically over a few weeks. The interval it takes for the Cepheid to complete one pulsation is a direct indication of the stars' intrinsic brightness. This value can be used to make a precise measurement of the galaxy's distance.
The precise measurement of this distance allows astronomers to calculate that the universe is expanding at the rate of 80 km/sec per megaparsec (+/- 17 km/sec). For example, a galaxy one million light-years away will appear to be moving away from us at approximately 60,000 miles per hour. If it is twice that distance, it will be seen to be moving at twice the speed, and so on. This rate of expansion is the Hubble Constant.
These HST results are a critical step in converging on the true value of the Hubble Constant, first developed by the American astronomer Edwin Hubble in 1929. Hubble found that the farther a galaxy is, the faster it is receding away from us. This "uniform expansion" effect is strong evidence the universe began in an event called the "Big Bang" and that it has been expanding ever since.

To calculate accurately the Hubble Constant, astronomers must have two key numbers: the recession velocities of galaxies and their distances as estimated by one or more cosmic "mileposts", such as Cepheids. The age of the universe can be estimated from the value of the Hubble Constant, but it is only as reliable as the accuracy of the distance measurements.

The Hubble constant is only one of several key numbers needed to estimate the universe's age. For example, the age also depends on the average density of matter in the universe, though to a lesser extent.


Observer´s Log

Spiral Galaxy
Dreyer description: Very remarkable! Pretty faint, very large, round, very gradually, pretty abruptly brighter middle resolvable, but mottled nucleus, 2-branched spiral; = M100.
Other ID: UGC7450
Other ID: MCG3-32-15
Other ID: MESS100
Other ID: PGC40153
Magnitude: 10.2
RA: 12h 23m 05.5s Dec: +15°48'20"
RA: 12h 22m 55.2s Dec: +15°49'23" (Epoch 2000)
Size: 7.5' x 6.4'
Position Angle: 30.0







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This site was last updated 2006-04-22                                                                                                          Site created and maintained by Jorge Lázaro