• Rotation curve: Not only indicates presence of dark matter, but also tells us how it is distributed
• Spiral galaxies: Dust, cold gas, bluish because of star formation; have bulge, disk, halo. Sa larger bulge, more tightly wound than Sc. Can be barred.
• Elliptical galaxies: Not much dust, reddish because lack ongoing star formation, so blue stars already dead and gone. E0 is spherical, E7 looks like cigar.
• Lenticular galaxies: Have disk but no arms or star formation, lack dust/gas in disk
• Irregular galaxies: Often look like shredded spirals, or else remnant of collision or intense star formation

• Microlensing: Dim object briefly lenses and brightens light from background source when they line up exactly; use to find dim objects
• Hubble tuning fork: Proposed as evolutionary scheme, still useful to categorize galaxies
• Tully-Fisher relation: Luminosity of spirals related to rotation speed; faster rotation means more luminous

Just in time for a summer holiday, scientists have discovered the solar system's newest beach destination. Too bad there's no way to get there - at least not easily. Researchers report in Nature today that they identified a dark liquid lake, surrounded by a lighter shoreline and a "beach," on the surface of Saturn's moon Titan. The foot-shaped lake is the first verified extraterrestrial body of liquid, and is likely filled with hydrocarbons, simple compounds also common on Earth.

"This is the first definitive evidence for both liquid and liquid hydrocarbons on Titan," says lead study author Robert Brown, a professor of planetary science at the University of Arizona's Lunar and Planetary Laboratory (LPL) in Tucson.