Imagine having millions of stars and planets at your fingertips, without spending thousands on a telescope or shivering all night under a cold, dark sky.
The universe is online, available from the comfort of your computer chair. It's a feature that Google developers, in collaboration with astronomers, have added to Google Earth, the Web site that provides millions of users with bird's-eye views of their home planet.
Sky at Google Earth, which made its debut in cyberspace early yesterday, turns Googlers around and aims their eyes toward the heavens, with user-friendly tools for navigating and zooming deep into the skies of both the Northern and Southern hemispheres.
In the background there are 100 million individual stars and 200 million galaxies. They're not randomly generated dots, but real, digitized photos -- a million of them -- stitched seamlessly together from some of the world's most complete sky surveys.
Astronomers at the Space Telescope Science Institute in Baltimore have added 127 high-resolution digital photographs from the Hubble Space Telescope. They've spent months patching them all into Google's sky at their proper zoomable distances and precisely in position.
"It's a very interesting tool to allow people, as never before, to browse the sky," said Alberto Conti, an institute astronomer and development manager for the institute's Community Missions Office, which works to make Hubble's discoveries accessible to the public.
Because of light pollution, he said, lots of people, especially in East Coast cities like Baltimore and New York, "have never really seen the sky." With Google Sky's software, they can "explore things they could never see with their own eyes, or things they probably would not see in a planetarium."
More overlays, or "mashups," available to Sky users can reveal the constellations, and identify stars and planets visible from their backyards. Sky can also forecast the positions of the moon and planets two months in advance.
"I'm looking forward to people adding asteroids, and things that are moving -- a lot of comets, you name it," Conti said. Just like Google Earth itself, Sky will allow users to form communities of common interest, and add their own images and lists of interesting sights.
Suggestions for still more additions to Sky -- including images in ultraviolet, X-ray or infrared wavelengths -- are already coming in, said Carol Christian, deputy at the institute's Community Missions Office.
"Since we're identified with the professional science community, we're getting feedback from them, and from our European colleagues," she said. "People want to jump in and add stuff, and we're happy they can do that."
Google Earth users can access the Sky feature from a View drop-down menu, or a Sky button on the toolbar. The Sky environment is navigated much like Google Earth, using drag, zoom, search, My Places and layer features.
With their cursors, users can steer easily around the sky, access Wikipedia information about the stars they're seeing, zoom deeper into space and take virtual tours of various kinds of galaxies and nebulas, and learn about a star's life cycle.
Conti said the user interface is simple and intuitive to use. "You start using the software almost immediately. It's very easy to add a place mark, add an image, save this, and share this with anybody," he said.
Although astronomy buffs for many years have used computer software to navigate the heavens, the programs rely largely on simulations, not real photos of the night sky. And none contain as many objects as Sky.
Google Earth was released in June 2005, and astronomers immediately saw the technology's potential to allow scientists and students to explore the sky and visualize objects captured by telescopes.
In a proposal to Google, Conti said, "we basically showed them how beautiful and complex scientific data is, and what we would like to do with the technology."
At Google, meanwhile, some people were already thinking along the same lines.
Chikai Ohazama, a Google Earth products manager, was walking down a hallway at the company's headquarters in Mountain View, Calif., when someone called him into an office to watch a demonstration of a program that "flew" him among stars and galaxies captured by the Sloane Digital Sky Survey. The images are the most comprehensive photo atlas of the night sky.
He was captivated.
"For me, it was the fact that there is so much in the sky you don't see from standing around on the ground and looking up," he said. "You saw galaxies everywhere, not just one here and one there. They're all over the sky!"
Google's Pittsburgh engineering team, with ties to Carnegie Mellon University, began developing the underlying software and assembling partners in astronomy. They eventually added the California Institute of Technology's Palomar Observatory, the United Kingdom Astronomy Technology Centre and the Anglo-Australian Observatory.
It wasn't always an easy collaboration.
Google's software engineers were accustomed to working with the Earth -- a globe, viewed from above, Christian said.
"These are geographic information systems people. They're used to dealing with a sphere from the outside," she said.
At first, they wanted to construct Sky the same way, as if the stars and galaxies were pasted to a spherical shell, with the observer outside looking in, instead of inside looking out.
"We were, like, 'You gotta be kidding,' " Christian said. "They didn't get it. We've had to educate them, too."
Sky in its final form does have users looking out from the Earth, as they should. But to make that happen, the astronomers had to integrate their data in reverse, like reading a road map in a mirror.
Each high-resolution Hubble image then had to be painstakingly positioned on the Google sky, with precisely the right orientation, and at the proper distance for users who zoom toward each one.
They were added to a full-sky panorama of millions of background stars and galaxies, taken in the 1980s and 1990s, at various resolutions, by Sloane and another sky survey called the Digital Sky Survey Consortium.
As with Google Earth, users will see some parts of the sky at higher resolution -- with finer detail -- than other parts.
Sky's designers intend their platform to be a dynamic one, ready to accept new imagery and new astronomical phenomena as they occur, or as they're discovered.
Astronomers at the Space Telescope Science Institute are already collaborating with the Gemini Observatories in Hawaii and Chile, whose astronomers want to contribute imagery. "Our goal is to make it easier for other observatories and amateur astronomers ... so others don't have to go through what we did," Christian said.
Conti and Christian are also hopeful that, in time, Sky at Google Earth will become an information hub for scientists.
That's fine with Google.
Part of its business plan is to "just have that community grow," said Ohazama. "Just as you see mashups created by Google Earth and Google Maps, we see that also for the astronomical data -- having that data grow and over time benefit everybody."
Astronomers are already pitching new ideas for the site.
"I thought we were going to take a breather" now that Sky is up and running," Christian said. "But people are sending in so many suggestions, we have to get our thoughts together and figure out exactly what we want to work on."
Sky at Google Earth is available on the newest versions of Google Earth, which can be downloaded for free at http:--earth.google.com