By Jonathan Fildes

Science and technology reporter, BBC News



Imagery for the system came from six research institutions

Google developer describes Sky's techniques

The tool is an add-on to Google Earth, a program that allows users to search a 3D rendition of our planet's surface.

Sky will allow astronomers a chance to glide through images of more than one million stars and 200 million galaxies.

Optional layers allow users to explore images from the Hubble Space Telescope as well as animations of lunar cycles.

"The basic idea is to take Google Earth and turn it on its head," Ed Parsons, Geospatial technologist at Google told the BBC News website.

"So rather than using it to view imagery of the Earth, use it to view imagery of space."

Dr John Mason of the British Astronomical Association, Britain's largest body for amateur astronomers said: "Light pollution and air pollution is now so bad in many areas that all you can see when you look up is a few dozen stars.

"If this helps people to realise just what they are missing, it is a jolly good thing."

Clear view

To use the new system, users will need to have Google Earth installed on their computer.

Digital astronomers can then zoom into an area from which they want to view the night sky.

SKY LAYERS Constellations: Connects stars and labels with name Backyard astronomy: Information on objects visible to the eye and small telescopes Hubble Space Telescope Imagery: 129 high-resolution pictures from Hubble Moon: Two months of lunar positions and moon phases Planets: Positions of seven planets two months ahead Users Guide to Galaxies: Virtual tours through different types of galaxies Life of a star: The different stages of a star's life cycle

"Click a button and the world flips round and you see the sky from that particular location," explained Mr Parsons. "[The view] would be the constellations that you would see oriented in the sky on that particular day at that particular time."

Users can overlay the night sky with other information such as galaxies, constellations and detailed images from the Hubble Space Telescope.

Imagery for the system came from six research institutions including the Digital Sky Survey Consortium, the Palomar Observatory in California and the United Kingdom Astronomy Technology Centre.

Much of the imagery can be found through searches on the internet but Google hope the add-on will be simpler and more fun.

Mr Parsons said: "The sky you will be seeing will be a completely clear and you will be able to see objects which are very faint indeed - that you can only see with very large telescopes."

Virtual tour

Sky is not the first time Google has ventured into space.

In March 2006, the company launched Google Mars which allows users to explore the surface of the Red Planet.

Nasa' and Google signed an agreement in December 2006

Another service, Google Moon, lets users view the sites of the Apollo moon landings.

Both services use data from the US Space Agency Nasa, with which Google signed an agreement in December 2006.

The Space Agreement Act was intended to put "the most useful of Nasa's information on the internet".

At the time, Nasa administrator Michael Griffin said the agreement would soon allow "every American to experience a virtual flight over the surface of the moon or through the canyons of Mars".

The two organisations also said they would collaborate in a variety of areas including adding data collected by Nasa to Google Earth.

However, Mr Parsons said the latest tool was not a product of the partnership.

Mass market

Google Sky is not the only tool that allows astronomers to explore the night sky from their computer.

Stellarium shows the night sky in 3D

For example, Stellarium is a free open source tool that gives people a chance to access more than 210 million stars, in addition to planets and moons.

The software is the brainchild of Fabien Chereau, a Research Engineer at the Paris Astronomical Observatory, and is used in many planetariums.

Like the suite of Google applications, it allows people to explore places of interest on Earth, as well as mission sites on the Moon and Mars.

Commercial alternatives also exist, such as Imaginova's Starry Night, that offers a range of software packages aimed at beginners to "the serious astronomer".

Apple Mac users can download a Starry Night widget that will allow them to see the night sky from any location on Earth.

"The other astronomy packages are designed for maybe the more professional amateur market," said Mr Parsons. "We are aiming this more at the mass market. If people get hooked and interested they may migrate to these other packages."