GalaxyZoo

If you're following ADYK, you've just learned about spiral and elliptical galaxies, and the Hubble classification scheme for galaxies. Astronomers have so many pictures of galaxies from various telescopes, and need help classifying all of them. Don't worry, there's no need to memorize the Hubble tuning fork or even know anything about galaxies! If you can look at pictures and answer some simple questions then you're good to go!

GalaxyZoo.org is part of NASA's zooniverse project. Zooniverse is a website where the general public can help astronomers study real astronomical data from telescopes. Basically you chose from a variety of tasks, such as classifying galaxies, measuring moon craters, looking for supernova, searching for exoplanets, etc., go through a short training session, and now you are the astronomer! The general public has helped astronomers make many new discoveries, just by spending a little time on zooniverse.  Check out GalaxyZoo today, maybe you will be the next one to make a big discovery!

Hubble Classification of Galaxies

The Hubble tuning fork diagram was developed by Edwin Hubble as a way of classifying galaxies based on their shape. Basically, astronomers look through a telescope at a galaxy, and classify it as an elliptical, spiral, or barred spiral. These classifications were discussed in the last ADYK. If the galaxy looks like a fuzzy bright blob, it's classified as an elliptical (E), and a number is assigned based on how round it looks (1=circle, 9=cigar shaped). If a galaxy has deifned circular rings, but not exactly spiral arms, then it's an "S0".  If the galaxy appears to have spiral arms, it's either a regular spiral galaxy (S), or a spiral with a bar like structure through the center (SB). They are also assigned a letter based on how tightly wound the spiral is. "Sa" means tightly wound arms, while "Sc" is very loosely wound arms. These classifications are handy for astronomers, as they can relate the properties of galaxies to their classification. Hubble originally thought that this diagram represented a time sequence, i.e. all galaxies started as round ellipticals (E0), and evolved over time into spirals (SBc or Sc). Astronomers are now able to measure the ages of many galaxies, and we've found some young ellipticals and old spirals, so the tuning fork diagram does not represent a galaxy evolution sequence. One thing to remember is that this classification is based on actual galaxy shape, not observed. For example, from Earth's perspective, you might view a spiral galaxy edge on, but think it's an E7 elliptical because it appears that way. Because of this, it's not easy to classify these galaxies accurately. You can actually help astronomers do this! Check out the next ADYK!