Researchers reveal the biggest digital survey of the Milky Way to date

Centre of the Rosette nebulae as imaged with IPHAS Photo: Astro Grid (

December 31, 2007 More than 50 astronomers from the UK, Europe, USA and Australia have joined forces to produce the first comprehensive optical digital survey of the plane of the Galaxy. The Initial Data Release (IDR) from the INT Photometric H-Alpha Survey (IPHAS) includes around 200 million unique objects available via an online database, forming a huge resource designed to boost our understanding of stellar evolution and further the study of stellar demographics of the Milky Way and of its three-dimensional structure.

Data for the survey, which contains stunning red images of nebulae and stars, was obtained by looking at light emitted by hydrogen ions using the Wide Field Camera (WFC) on the 2.5-metre Isaac Newton Telescope on La Palma. The initial data covers observations of the Northern Plane of the Milky Way over 1600 sq deg, in two broadband colours, and a narrow band filter sensitive to the emission of Hydrogen in the red part of the spectrum (H-alpha emission). To put the scope of the study in perspective, the moon on the sky as seen from Earth covers approximately 0.1 square degrees. Eventually the IPHAS survey will be extended to the Southern Galactic plane of our galaxy to produce a coverage of around 4000 square degrees containing up to 800 million objects.

Professor Janet Drew of the University of Hertfordshire said “Using the distinctive Hydrogen marker we are able to look at some of the least understood stars in the Galaxy – those at the early and very late stages of their life cycles. These represent less than one in a thousand stars, so the IPHAS data will greatly improve our picture of stellar evolution.”

In addition to traditional web access, the data is being published via the AstroGrid Virtual Observatory interface which enables cross-referencing with other data catalogues.

“Access through the AstroGrid Virtual Observatory opens up a full range of analysis options and should allow astronomers to make greater use of the information. IPHAS is the largest dataset published primarily through Virtual Observatory interfaces to date, and as such heralds the future of survey data mining,” said Dr Nic Walton of the University of Cambridge.

Access to the IDR is available via the web at, or through the public IPHAS site.

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