Cosmic Collisions

Frequently Asked Questions

The galaxy that I'm looking at is really low resolution and doesn't look like any of the categories here. How do I classify that?
Objects that are incredibly low resolution (only a few pixels across and generally circular) are point sources, and have their own category. These are objects that are too small to be resolved clearly. Objects that are larger than point sources but still difficult to see clearly require a bit more judgment. You should choose the answer that most closely matches the examples given.

How do I tell the difference between a spheroid and a point source?
A point source will be small, only a few pixels across at it's brightest, with no structure outside of this. A spheroid may have a central feature which looks like a point source, but it will spread out further. Very bright point-sources, like stars, will also have a telltale snowflake pattern, which is due to the way light moves through JWST. Faint point sources, however, may just look like very small spheroids. If you're unsure, try counting the pixels.

How do I tell the difference between a face-on disk and a spheroid?
A face-on disk will often - but not always - have some internal structure beyond a core and outskirts. In addition, disk galaxies tend to be fairly bright across their whole surface. A spheroid is brighter in the center and dimmer into the outskirts than a face-on disk, and is more likely to appear internally smooth.

There are certainly some disks without this telltale internal structure, especially at low resolution, and for those objects, there isn't a good way to distinguish between face-on disks and spheroids, so in those cases, you will just have to use your best judgment.

How do I decide if an irregular galaxy is a merger or not?
In general, try to look for the specific merger signatures outlined in the field guide; multiple nuclei sharing a common envelope, tadpole-like tidal tails extending away from the galaxy, and companions that are visibly interacting and distorting the object. If a galaxy is distorted/irregular but lacks these features, it may just be a galaxy in the early universe that is still in the process of coalescing.

What if I see something that doesn't match any of the examples?
Galaxies are very diverse and come in all shapes. It's possible that you're seeing a galaxy of a type we haven't named yet and didn't consider when we made our categories! In this case, you should choose the answer that most closely matches the examples given, and then tell us about it in the talk page so we can get a look at it ourselves!

I see a bright spot in this galaxy. Is it a supernova?
We can't rule it out without further investigation, but probably not. Supernovae CAN shine brightly enough to be visible within to their hosts out to pretty high redshift, and are a significant piece of the cosmic distance ladder. However, supernovae are fairly rare - most nearby galaxies will only undergo one supernova every century, and supernovae are only visible for a few days or weeks. While they're more common in the earlier universe, we would still need to have a much larger sample to expect to spot even a handful of these. That doesn't mean that the bright spot ISN'T a supernova - it just means there are more likely explanations, like a central bulge, a knot of star formation, or an AGN.

To rule out a supernova, we would need to look at observations of the same system at different times.

Do these images show what the galaxies would actually look like, if we could see them with our eyes?
For many of them, yes! JWST observes at much redder wavelengths than our eyes can see. Our eyes observe wavelengths of light 0.3 to 0.7 microns (you might have heard it as 300-700 nanometers - these are equal!); JWST observes from 0.7 to 25 microns. As light moves through the universe, it stretches out due to the expansion of space, so light that was emitted at a blue wavelength may arrive at a redder one. When possible, we use the this effect to match JWST observations to their emitted colors in the visible spectrum, in order to best match what your eyes would see. This is not always possible - when its not, we just display the available colors instead.

What if I classify a galaxy "incorrectly?"
These images will be seen many people, so don't worry if you aren't completely sure about your answers. One uncertain answer won't throw off the overall result, and if everyone is uncertain then that will be displayed in an inconclusive classification result.

Will I get credit for helping out here?
Yes, if you included your real name in your Zooniverse account and helped classify galaxies for us, you'll be included in the acknowledgements section of any paper that gets published using this data. If there are too many classifiers to do that effectively, we'll include acknowledgments as supplemental materials to those papers.