One of the most addictive free software offerings on the Internet is Google Earth, which we first told you about nearly two years ago.

This free software lets you quite literally zoom in on any place on the planet. It's good for hours of exploration.

But now Microsoft has turned the Google Earth concept upside-down and inside-out with something called WorldWide Telescope.

"You basically can look at any part of the sky in almost any wavelength, from infrared to X-ray," said Curtis Wong, the group manager of Microsoft's Next Media Research Group. "You can zoom right in to the center of a galaxy."

WorldWide Telescope offers a look at the stars and other celestial bodies you just can't get in a textbook — or even in a planetarium.

The concept is similar to Google Earth; download the software, connect to the Internet, and you can get a limitless perspective on our universe by pointing and clicking in the sky.

WorldWide Telescope delivers 3-D views of our planets. By "flying" around Mars, you can see the mountainous terrain and zoom in on interesting features using both telescope imagery and photos sent back by interplanetary probes.

There are even a series of breathtaking panoramic views from the Mars Exploration Rovers, Spirit and Opportunity. From the perspective of the rover's camera, you get a 360-degree look at the Martian terrain, just as though you were standing on the surface yourself.

WorldWide Telescope can give you an animated look at the mechanics of a solar or lunar eclipse.

By telling the software where you live, it can present a replica of the night sky in your own backyard. So take the notebook computer with you for an interactive way to identify the stars and planets.

Google Earth makes geography fun, and WorldWide Telescope does the same thing for astronomy. It's already sparking a sense of extratrerrestrial enthusiasm with others, including future young scientists.

Taking advantage of WWT's ability to let users create their own stories, a six-year Canadian boy old named Benjamin offered his own tour of the Ring Nebula.

"I read that it's 2,300 light years away, which seems like a very long bike ride!" Benjamin says with a giggle.

"This whole process of interacting with the sky within this virtual environment maps that same knowledge about where things are in scale and stories into the real world," Wang said, "and that's what we're really excited about as an educational tool."

WWT is a free download, available only for Windows computers. It requires an Internet connection for most features, but it can operate untethered with some limitations if you want to use it in the field.

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E-mail askwalt@wfaa.com