Edwin HubbleEdwin Hubble

An Astronomer at the Mount Wilson An Astronomer at the Mount Wilson Observatory in California.Observatory in California.

The Milky Way GalaxyThe Milky Way Galaxy

Hubble Space TelescopeHubble Space Telescope

Named in Honor of Astronomer Edwin HubbleNamed in Honor of Astronomer Edwin Hubble Launch Date April 24, 1990Launch Date April 24, 1990 Mission Ends: ~2010Mission Ends: ~2010 The size of a tractor-trailer The size of a tractor-trailer 375 miles above Earth375 miles above Earth Orbital period around Earth:Orbital period around Earth:

96-97 minutes96-97 minutes

Edwin HubbleEdwin Hubble

In the 1920’s, Edwin Hubble discovered In the 1920’s, Edwin Hubble discovered that what appeared to be “stars” from that what appeared to be “stars” from earth were actually galaxies.earth were actually galaxies.

Some nebulae, or large clouds of dust and Some nebulae, or large clouds of dust and gas, were actually discovered by Hubble gas, were actually discovered by Hubble to be galaxies beyond even our Milky to be galaxies beyond even our Milky Way. Way.

DefinitionDefinition

A galaxy is a group of stars held together A galaxy is a group of stars held together by gravity.by gravity.

ClassificationClassification

Hubble classified galaxies according to Hubble classified galaxies according to their shape.their shape.EllipticalEllipticalSpiralSpiralBarred-spiralBarred-spiral IrregularIrregular

Elliptical GalaxiesElliptical Galaxies OldOld Little or No Gas or Little or No Gas or

DustDust Emit Radio WavesEmit Radio Waves Classified with the Classified with the

letter Eletter E Sample Shapes…Sample Shapes…

Spiral GalaxiesSpiral Galaxies

Have Young, Hot StarsHave Young, Hot Stars Have a lot of Gas & DustHave a lot of Gas & Dust Arms spiral out from the centerArms spiral out from the center Classified with the letter SClassified with the letter S

The Whirlpool GalaxyThe Whirlpool Galaxy

Barred-Spiral GalaxiesBarred-Spiral Galaxies

Central bar shape, made of starsCentral bar shape, made of starsArms spiral out from the elongated centerArms spiral out from the elongated centerClassified with the letters SBClassified with the letters SBThe Milky Way galaxy is an example of a The Milky Way galaxy is an example of a

barred-spiral galaxybarred-spiral galaxy

Irregular GalaxiesIrregular Galaxies These Galaxies Have No Dominant ShapeThese Galaxies Have No Dominant Shape No rotational symmetryNo rotational symmetry Tend to be PatchyTend to be Patchy Classified with the letter IClassified with the letter I

Hubble’s LawHubble’s Law

Hubble discovered that all Hubble discovered that all galaxies are receding galaxies are receding from the Earth with from the Earth with velocities that increase in velocities that increase in proportion to their proportion to their distance from us.distance from us.

This discovery showed This discovery showed that the universe is that the universe is expanding. Hubble expanding. Hubble proved Einstein right!proved Einstein right!

Farthest Known GalaxyFarthest Known Galaxy

The Eagle NebulaThe Eagle Nebula

Photo CreditsPhoto Credits

All Images taken from:All Images taken from:

http://www.exploratorium.edu/hubble/live/http://www.exploratorium.edu/hubble/live/webcasts.htmlwebcasts.html

Andromeda GalaxyAndromeda Galaxy

The largest visible The largest visible galaxy (200,000 ly in galaxy (200,000 ly in diameter), diameter), Andromeda has the Andromeda has the most stars of any most stars of any local group galaxy, local group galaxy, about 300 billion about 300 billion compared with our compared with our 200 billion stars.200 billion stars.

The Sombrero GalaxyThe Sombrero Galaxy

Strange GalaxiesStrange Galaxies

What types of galaxies can you see in this Hubble mosaic?

Major Types of GalaxiesMajor Types of Galaxies

Most galaxies are spiral, elliptical (giant or dwarf), or irregular galaxies. At right is the Large Magellanic Cloud, an irregular galaxy orbiting the Milky Way.

http://www.seds.org/messier/m/m087.html

http://www.seds.org/messier/xtra/ngc/lmc.html

Strange GalaxiesStrange Galaxies

Some galaxies are difficult to classify, like the Ring Galaxy, which is an odd spiral. The Sombrero Galaxy is a normal spiral, but looks odd in our side view. Some strange galaxies are the result of collisions with other galaxies. These collisions don’t mean stars hit one another…they just get mixed up.