Toolkit

Do you have an educational program or web site? Do you want to make it better by adding real astronomy data, the same data that professional astronomers are currently using to study the sky? The NVO can supply you with complete data for billions of sky objects, in all wavelengths, and we're happy to help people connect to the data we provide. Once you get your program up and running, we will advertise it here on virtualobservatory.org.

The first step is to let us know that you'd like to add data to your project through the NVO. Then, we'll work with you as you connect your project to NVO tools and services.

The rest of this page provides "a look under the hood" at some of the web technology that makes the NVO work.

Web Services

The heart of the NVO is in web services. When your computer accesses a web site, your computer (the client) requests that information be transferred from a distant computer (the server), which could be anywhere in the world. When your computer accesses a web service, the client asks the server to run a program using inputs provided by the client, then to return the output to the client.

The NVO's tools are web services, programs located on servers around the U.S. Your computer asks the web services on the servers for the data you want, and the web services return the data you asked for.

Application Programming Interfaces (APIs)

The most efficient way for your computers to talk to the NVO's web services is through Application Programming Interfaces (APIs). APIs are web commands that tell the web services exactly what inputs you are providing. APIs take the form:

url?input1=value1&input2=value2...

with the URL of the web service, a question mark, and a list of the inputs to the web services separated by ampersands (&).

An example should help make this clearer. You may have seen SkyServer, the EPO website of the Sloan Digital Sky Survey (SDSS). SkyServer includes a Navigation Tool where you can enter a right ascension and declination to see SDSS data for any part of the sky. The Navigation Tool can be accessed from the SkyServer web site by clicking the link above, entering the RA and Dec you want, and clicking Get Image. But the tool can also be accessed through an API. The URL is http://skyserver.sdss.org/en/tools/chart/navi.asp . The inputs for the web service are the right ascension (RA) and declination (dec) of the point you want to see.

How would you access the Navigation Tool through an API to see SDSS data for RA = 0, dec = 0? If you do it right, you should see the data. The answer is at the bottom of this page.

NVO Web Services and their APIs

All the services of the NVO are listed at the NVO services web site, www.voservices.org/. The services are divided into different types. For example, Spectrum Services lets you connect to spectral data, the Filter Profile Service lets you connect to data about telescope filters for observing, and the NED services let you connect to the NASA Extragalactic Database (NED) to find names and coordinates of objects. Within each service, click on the "Web Services" link for information on what the service is and how to connect to it using its API.

Happy Developing!

You should now know enough of the basic concepts of web services to begin to develop connections between your products and NVO's services. You will probably still run into some trouble with the specific syntax and capabilities of the NVO services. Contact us, and we'll find someone who can answer your questions.

Navigation Tool API answer:
http://skyserver.sdss.org/en/tools/chart/navi.asp?ra=0&dec=0