Using the Virtual Observatory

Show Virtual Observatory
Show Virtual Observatory

With the Virtual Observatory you can search for and download images from 10+ professional astronomical image archives. Choose Show Virtual Observatory (⇧⌘F), or click the last of the four View buttons in the toolbar, and the center of the library window will be replaced by the Virtual Observatory, as are the inspectors.

Virtual Observatory
Virtual Observatory

Along the top you’ll find a row of buttons, one for each archive. Each of these buttons acts as a toggle, determining whether or not the selected archive will be searched. Below it is a text field where you enter the name, identifier or coordinates of the object you are interested in. By default Observatory will do an image search with a radius of 10 arcminutes, which is a little less than the angular diameter of the full moon. You can change this in the Search Radius field.

The supported archives are:

To search for an object, enter its name, identifier or coordinates in the text box below the buttons. Observatory recognizes Messier, NGC/IC, Tycho–2 and PGC2003 identifiers, as well as hundreds of common names. Entries like “Whirlpool Galaxy”, “M 51”, “202.4696+47.1953” and “13 30+47 12” (without quotes) will all be resolved.

As soon as you enter anything, the resolved items with their celestial coordinates will be displayed immediately below the text field. For example, if you start entering “Whirlpool Galaxy”, without quotes, Observatory will display

Typing “Whirlpool Galaxy”
Typing “Whirlpool Galaxy”

after you have typed the “W”. The list will be further reduced as you type.

Typed “Whirlpool Galaxy”
Typed “Whirlpool Galaxy”

If the object you want to obtain images for is in the list, select it and click the Search button. Observatory will then search for all images in the selected archives, and display the results.

Although Observatory contains data for millions of objects, you may find that it cannot always resolve the object you are looking for. For this reason, the SIMBAD and NED web services are integrated with the Virtual Observatory. After entering the target name or identifier, just click the corresponding buttons to have these services resolve your entry and add them to the list.

The results are initially sorted by exposure date, but you can change this by clicking one of the column headers. By clicking a second time, you change the sort order.

Your search may return thousands of results. One way to reduce the number of results is by deselecting the archives you are not interested in. You can reduce or extend search results this way even after you have performed the search. By reducing the search radius, the number of results will also be reduced.

Another way to reduce the number of search results is by filtering them using the Virtual Observatory Results Filter.

Virtual Observatory Results Filter
Virtual Observatory Results Filter

It allows you to reduce the number of results by target, instrument, filter name, description or identifier. You can specify which field you want to match, or you can have it match any of these fields by using “All”. For example, if you only want to include images obtained with the Hubble ACS instrument, you might enter “ACS” here.

Filter by HST ACS instrument
Filter by HST ACS instrument

If you select one or more results, the inspector on the right hand side will display more details of the selection. For many items preview images are available, which is indicated by a dot (). By expanding the Preview pane in the sidebar, you have quick access to these previews.

Items you have already in your library are gray in the results table. Sometimes you will also see items in red. This indicates that the data is still under the proprietary period.

To download images, select them and click the Import button. If you have selected the Add to album checkbox, they will be imported straight into the album that you have currently selected in the sidebar, if any, instead of becoming “Unfiled”.

Whirlpool Galaxy
Whirlpool Galaxy

The images will be downloaded and imported in the background, and you can continue to search for other images or use Observatory in any way you wish. If you quit Observatory then any ongoing downloads will be cancelled though.

You can view the progress of downloads by clicking the Downloads button in the toolbar. In that popover, you can also cancel individual downloads, as well as clean up the list such that only downloads that are in progress are displayed.

The downloaded images are stored as Managed Master images in your library. If you wish to have access to them from outside Observatory, then you’ll need to export them by choosing File ▸ Export ▸ Managed Master…. This exports the original downloaded files.

If you press the key while selecting the Show Virtual Observatory menu item, it will change into Match Virtual Observatory (⌃⌥⌘F). If your currently selected image is Astrometric Matched, the Virtual Observatory will then use its center equatorial coordinates to initiate a search right away. This is handy way to search for images in the archives that cover the same area as your selected image.