The NVO DataScope tool queries hundreds of astronomical services about a given location or region and organizes the information so that you can browse it, select data for download, or pass it into compatible tools for further analysis
Once you submit a query DataScope will start a query of registered resources that can be queried at that position. A result form will pop up and show you the kinds of responses you get.
If you wish to make sure to get fresh results you can click checkbox that skips the cache. Similarly the DataScope checks once an hour to see what resources are available to be queried. You can ask for this to be updated before your query by checking "Refresh registry" box.
A few recent queries are shown at the bottom of the page but you can leave your query off the list by clicking on the third checkbox.
The DataScope should immediately return with a page that begins to organize the results. If the results have already been cached the form will show the previously queried data. If you are starting a new query it will gather results over a period of a few minutes. A status section at the top of the query result page shows the progress of the query, the number of resources found and how long ago the query was initiated. All other data is organized into tabbed panels below the status area You can jump to any of the panels at any time. Just click on the panels' tabs at the top of the page.
This is where where you launch analysis tools like Aladin or initiate a download of data to your local machine of the selected files.
What's the difference between Images and Observations?
The Image services are those services which return images regardless
of the origin, e.g., the image may be dynamically generated from
survey data, or it may correspond to a single observation of some
observatory. An observation is a single collection of data taken
by an observatory typically of some target for a given observer.
There may or may not be images that were taken as part of any given
observation. For observations in many cases DataScope gives links to the archive
data for an observation, but this is not always possible, sometimes
only a table of the characteristics of the observation is available.
The observation
data may include spectra and time series as well as or instead of observations.
Sometimes a data provider will provide multiple methods of accessing their data so that DataScope lists the service in both the Images and Observations area. To summarize, the Images links will always have some underlying data. Observations links may or may not have links to underlying data, and can also include spectra and other non-image types of observations.
You can control which categories are displayed. Each category label
is preceded by a minus sign, e.g., 
Major Multiwavelength Services,
Click on the 
to collapse the category.
The resources in that category will disappear.
Just the label will be left, preceded by 
(N) where
N is the number of resources in the collapsed tree.
Click on the + to restore the category.
Each resource is displayed in the format
Click on the Name to display the data returned by
the resource. This will be displayed in the Data panel and you'll
move there automatically.
The '?' links to the metadata for the resource, i.e., a structured
description of the resource as a whole.
Use the checkbox to select this table data for further analysis in Aladin or OASIS or to download the data. (See the Summary panel.) This checkbox selects only the table data. If there are FITS files indexed by this table, then you first need to view this table by clicking on the name, and then select the FITS images you wish to analyze.
To keep the page manageable, short names are used to describe the resource. To get a longer name let your mouse hover over a name for a second. A tool-tip box should appear giving more information about the resource. For still more data click on the ? to get the full metadata on the resource.
After the name the number of rows in the resource is given. This is given as (m/n) if there are FITS files indexed, or just as (n) if this is a table that does not index any FITS files. The value m gives the number of the FITS files that you have currently selected, while n gives either the number of rows in the table, or the number of FITS files available if any.
For many resources (MAST and HEASARC archive tables, ADS, NED and SIMBAD) the DataScope provides links into the native services. There may be a "Data" link at the beginning of each row, or one of the columns may be a link into the system.
If the row indexes a FITS file, then there will be a checkbox at the beginning of the row. Just click on the checkbox to select that file for further analysis. This works like a shopping cart. Go to the Summary page when you have made all of your selections and are ready to save the data or send it to an analysis tool.
For rows linking to FITS files there will be View and FOV links. the first links to a program that renders the FITS file for quick look viewing. The second outlines the region contained in this file over an optical image of the region.
There will also be View links for rows that link to non-FITS files. These just download the linked data (typically GIF or JPEG images, or occasionally HTML pages).
The top of the Data Table panel includes a number of links.
Timeout errors may indicate that the service was simply too busy to return data in the time alloted. A FileNotFound exception indicates that the URL is invalid. There may also be parsing errors for some services.