Author Topic: Finding information for your target object  (Read 15472 times)

Alice

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Finding information for your target object
« on: October 30, 2007, 11:47:42 pm »
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 . . .

------------------------------------------------------------------------------------------------------------------------------------------


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 number
For a discussion on redshift, see this link: Redshift = Distance?
For a tutorial on galaxy spectra, see this link: Tutorial bits on galaxy spectra

The 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 window

Using 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 window

The 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 SIMBAD

http://vizier.u-strasbg.fr/viz-bin/Otype?Radio

This 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.
« Last Edit: August 03, 2008, 05:25:49 pm by Infinity »

njtm

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About Geoff's "Finding info for your target.."
« Reply #1 on: October 31, 2007, 06:16:38 am »
That's a great explanation Geoff. I have one question about the "neighbours" page. Could you explain why the "distances" can differ from the "z"??

Alice

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Re: Finding information for your target object
« Reply #2 on: October 31, 2007, 09:58:54 am »
Comments welcome. If anything in it really needs changing, I'll update it in the original post.  :)

Geoff

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Re: About Geoff's "Finding info for your target.."
« Reply #3 on: October 31, 2007, 10:00:51 am »
Thanks for reminding me about this njtm.  The distances on the Neighbors link are misleading and don't directly relate to a distance from "us". I think they are relative distances between the objects on the photographic plate.
There is a post somewhere that discusses this and I have been meaning to find it and link to it from the FAQ.

Will hopefully do that later today.

Geoff

  Sometimes I think we're alone. Sometimes I think we're not. In either case, the prospect is staggering!- Arthur C. Clarke

Alice

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Re: About Geoff's "Finding info for your target.."
« Reply #4 on: October 31, 2007, 10:04:21 am »
Hey, now Geoff's topic's unlocked, I've merged this topic in! :)

ElisabethB

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Re: About Geoff's "Finding info for your target.."
« Reply #5 on: October 31, 2007, 10:13:27 am »
Thanks for reminding me about this njtm.  The distances on the Neighbors link are misleading and don't directly relate to a distance from "us". I think they are relative distances between the objects on the photographic plate.
Geoff
Yes, they are the relative distances. As it says in the heading for Neighbors : "Neighbors within 0.5 arcmins of (ObjID)"

and thanks Geoff for an amazing job !  :)

Michael

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Re: Finding information for your target object
« Reply #6 on: November 07, 2007, 12:55:30 am »
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 . . .

-The coordinates on the SDSS page need to be converted to hh:mm:ss.xx in order to use on Google. Is there an easy way to do this ?

Michael--------------------------------------------------------------------------------------------------------------

May I expect an answer to this question ?

Michael---------------------------


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 number
For a discussion on redshift, see this link: Redshift = Distance?
For a tutorial on galaxy spectra, see this link: Tutorial bits on galaxy spectra

The 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 window

Using 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 window

The 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.

« Last Edit: November 09, 2007, 12:55:25 am by Michael »

mgmg

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Re: Finding information for your target object
« Reply #7 on: January 11, 2008, 08:11:27 am »
Hi !

This is my first post. I do'nt know if it is in the right place !

After every post with an image, could a "certified" astromer send the most valuable icon corresponding to it?

With icon, I mean : Elliptical, Mergers, etc. as we have to click in.

Furthermore, when we click the icon unknown or unclear, can we receive later the "right response", if any ?
(I suppose that the galaxies pointed unknown or unclear are re-examined, right ?)

And best greetings for the new year.
Marc G.

sonicboomboy

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Re: Finding information for your target object
« Reply #8 on: July 09, 2008, 03:04:50 pm »
Great post Geoff - explained a lot! As an amateur astronomer there is one major thing I need to know..:

I've found M100/NGC4321 in GZoo and found out what it was through SIMBAD.

SEDS says M100 has a "Visual Brightness 9.3 (mag)" and this is what I am used to as a guide for what to expect in a telescope, or what size telescope would be necisary to view the object.

The mag data in the SDSS ranges from [petroMag_r: 11.10] to [psfMag_r of 15.78] ... I had seen closer figures for objects using the petroMag_r data.

Which of these magnitude figures in the SDSS data would you say is a good representation of apparent magnitude as a guide for telescope users? (This also applies to using remote telscope's online, for eg somebody could login to a remote scope and image a GZoo object in higher resolution, as long as they know it is within reach of that sized scope.)

Edd

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Re: Finding information for your target object
« Reply #9 on: July 09, 2008, 05:09:50 pm »
For galaxies, I'd go with model mags. For stars, psf.
When I look up at the night sky and think about the billions of stars out there, I think to myself: I'm amazing. - Peter Serafinowicz

sonicboomboy

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Re: Finding information for your target object
« Reply #10 on: July 09, 2008, 05:22:46 pm »
Thanks Edd .. I've used a web based remote telescope online which is a 10" SCT based in Canada, made me think anything especially interesting with a sensible magnitude might be worth imaging through that. Also asking just out of interest... Cheers :)

graham d

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Re: Finding information for your target object
« Reply #11 on: July 09, 2008, 05:33:40 pm »
The sdss imaging uses a telescope that is somewhat bigger than a 10" reflector-
http://www.sdss.org/background/telescope.html
for info and links therein.

sonicboomboy

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Re: Finding information for your target object
« Reply #12 on: July 09, 2008, 05:45:38 pm »
Hi Graham, yes I'm aware of the size of the Slone scope, just I often find myself looking at interesting objects through Slone thinking how I'd love to see them in higher resolution. Maybe I'm under stating the image quality on the SDSS but it is a survey rather than Hubble art. Perhaps I'm also under estimating just how many galaxies have been imaged by professionals and serious amatuers; thinking I could image something with a 10" SCT than hasnt been imaged in such quality before?!
« Last Edit: July 09, 2008, 05:50:35 pm by sonicboomboy »

Supersymmetry

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Re: Finding information for your target object
« Reply #13 on: August 03, 2008, 02:33:36 pm »
FYI: The Z-number link is broken...

Infinity

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Re: Finding information for your target object
« Reply #14 on: August 03, 2008, 05:26:49 pm »
FYI: The Z-number link is broken...

Thanks for pointing that out, I've fixed it now ;)