To see a GSP sketch showing the measurements approximating the spirals, click below.Ĭredit: Comparison and M51 image copyright Brian Lula Hurricane Isabel, courtesy GHCC, NASAĮxplanation: Uncomfortably close hurricane Isabel (left) and 30 million light-year distant galaxy M51 actually don't have much in common. M51 has two (Fibonacci number) spirals in one direction. To see a GSP sketch showing the measurements approximating the spirals click below. The Location in the Sky of M51, theWhirlpool GalaxyĪn Estimate of one and two Spirals of M51 The smaller galaxy appearing below and to the left is behind M51 and is thought to be responsible for the spiral structure of M51. It is 23 million light years distant and is one of the brightest and most picturesque galaxies on the sky. The Whirlpool Galaxy is a classic Sc type spiral galaxy visible with binoculars in the constellation of Canes Venatici. Other spirals with loose spiral arms and a small bulge are classified as "Sc" ( M33, M74, M100 ) or "SBc" ( M83, M109 ), (Curious About Astronomy? Ask an Astronomer) Astronomy Picture of the Day ) M51: The Whirlpool Galaxy. Galaxies with prominent bulges and pronounced spiral arms are classified as "Sb" ( M31, M81 ) or "SBb" ( M95, NGC 4725 ). Galaxies with conspicuous bulges and tightly wound spiral arms are called "Sa" ( Sombrero galaxy ) or "SBa" ( NGC 3185 ). Those with pronounced bar structures in their centers are called "barred spirals" and are classified "SB" (examples are given in brackets). The young stars in the disk are classified as stellar population I, and the old bulge and halo stars as population II.Īstronomers classify spiral galaxies according to their appearance by using the Hubble scheme. The near-spherical halo surrounds the disk, and is thought to contain copious amounts of dark matter : matter that acts gravitationally like "normal" matter but that can't be seen! Astronomers infer the presence of this dark matter by the motions of stars and gas in the disk of the galaxy, as well as older stellar populations in the halo like globular clusters. The bulge is located at the Centrex of the disk and consists of an older stellar population with little interstellar matter. The gas, dust and stars in the disk rotate in the same direction around the galactic center at hundreds of kilometers per second and are often arranged in striking spiral patterns.
The disk contains a lot of interstellar gas and dust, and most of the stars in the galaxy. Spiral galaxies usually consist of three components: a flat disk, an ellipsoidal bulge and a halo. Galaxies that appear neither disk-like nor rounded are classified as irregular galaxies.
Elliptical galaxies are redder, more rounded, and often longer in one direction than in the other, like a football. Spiral galaxies look like flat disks with bulges in their centers and beautiful spiral arms. Types of GalaxiesĪstronomers classify galaxies into three major categories. Far beyond the Milky Way, there are billions of other galaxies - some similar to our own and some very different - scattered throughout space to the very limits of the observable universe. This band is the Milky Way galaxy - a gigantic collection of stars, gas and dust.
On a dark night, we can often see a band of light stretching across the sky.