The following topic was very kindly written by Geoff Roynon. Find your way around the SDSS page - what to most of us for some time is the page of "scientific gobbledygook"!
Over to you then, Geoff . . .
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This topic explains how to find out more about the object you have been asked to classify.
Before going into detail, it will make your task easier if you enable the “Tabs” option in your browser so you can have multiple windows open at the same time.
First, from the main GalaxyZoo classification window, click on the orange “Galaxy Ref:” link on the right-hand side of the window. This will open a new window, known as the “SDSS” window, also called “SkyServer Object Explorer” window.
This window shows a small picture of your object with cross-hairs and the remainder of the window contains various pieces of information which vary depending on the type of object and if a spectrum has been taken of the object or not.
The use of this window is described later.
You should now click on the picture of your object. This will open a new window called the “SDSS Finding Chart Tool”. This window has a larger picture of the area surrounding your object and there is a “zoom” tool in the left-hand margin to allow for zooming in or out. There are also various tools under the “Drawing options” header in the left-hand margin. See below for more information.
If you need to look at other objects near your object, you should click on the “Navi” link on the top left which will take you to the “SDSS Navigate Tool” window. This window is described further below.
SkyServer Object Explorer window (SDSS)
This window contains a lot of technical information. Some of the fields have links to a help page which explains the content of the field, e.g. if you click on the field called “camcol” it displays a page with a description of the data in this field. If you have the tooltips option set in your browser, you can hover your cursor over a field to see what units are used by that field. Many of the fields are only of use to astronomers or other experts.
The following fields may help in understanding your object (these fields will be found beneath the picture and are only present if a spectrum has been taken of the object):
“specClass” shows the spectral class of the object and should contain “GALAXY”. If it contains “STAR” then you should classify the object as “Star/Don’t know”.
“z” (redshift) - there are two fields labelled “z” on this window, the correct “z” field is the one beneath the picture (the “z” field to the right of the picture has something to do with the colour of the galaxy, NOT the redshift).
A “z” value of zero means that the object is in our galaxy and is probably a star.
“zConf” defines the confidence factor of the “z” value. A value of 0.9 or greater is good. If “zConf” is low (less than 0.5) it means that the “z” value is not to be trusted.
For a discussion on the “z” number, see this link:
Z numberFor a discussion on redshift, see this link:
Redshift = Distance?For a tutorial on galaxy spectra, see this link:
Tutorial bits on galaxy spectraThe left-hand column contains links to various tools. The following tools may help in some situations:
“Neighbors” this will display a list of any objects close to your object with their object id and type. For instance, if there is an object on top of your object or very close to it, you can click the Neighbors link and look at the first entry to find out what the other object is. If the other object is a galaxy you can click on the “objId” link to load the SDSS window for that object. This may have spectrum information and a “z” value which will help decide whether the other galaxy is close to “your” galaxy or not.
“NED”/”SIMBAD”/”ADS” search links. These links will search various catalogues for your object. For instance, if your object is a nice spiral you could click on the SIMBAD link and it may show a catalogue number which you can then look up in Google for more information.
Some objects will have multiple entries in these catalogues, depending on how “famous” they are and also if the object is composed of multiple objects, e.g. a galactic cluster.
SDSS Finding Chart Tool windowUsing the “zoom” tool in the left-hand column you can zoom in on your object if you need to check on which way a spiral galaxy is rotating, or you can zoom out if you need to see your object in context with its surroundings.
Under the “Drawing options” in the left-hand column, the “Invert image” will invert black and white in the picture. This can help when trying to find spiral arms in an image of a spiral galaxy.
If you suspect that your object is merging with another object or objects, the “Photometric objects” option may help by showing other possible objects within the main object.
SDSS Navigate Tool windowThe Navigator window has a picture of your object surrounded by a blue frame which is clickable and allows you to explore the area around your object.
Initially your object will be centred with a small green box surrounding it. On the right, in the middle, it shows a zoomed in view of your object and above that view is a box with some details about your object. The “type” field should be either “Galaxy” or “Star” but this field is not always correct so should be treated with caution.
You can explore other objects by clicking on them. The selected object will have a green box around it and the fields on the right will change to show information about the selected object. If you now click on the “Explore” field on the right-hand side, it will take you to the SDSS page for that object.
An excellent link to Object Classification in SIMBADhttp://vizier.u-strasbg.fr/viz-bin/Otype?RadioThis link contains a list of object types used by SIMBAD. When you use SIMBAD to find out more information about a specific object, the SIMBAD page contains an object type field called “otyp” which contains a short abbreviation of what SIMBAD thinks the object is. This link contains a table of these “otyp” abbreviations (called "Cond.") with a longer description ("Extended Explanation") which will help better describe what you have found.
