The University of Southampton

Largest digital survey of the Milky Way released

12 December 2007

Striking new colour images of our Galaxy have just been released by an international astronomical consortium, of which the University of Southampton is a member.

The images are from the first comprehensive optical digital survey of the Milky Way, a paper on which has been submitted to the Monthly Notices of the Royal Astronomical Society.

Conducted by looking at light emitted by hydrogen ions, using the Isaac Newton Telescope on the Canary Island of La Palma, the survey contains stunning red images of nebulae and stars.

Over 50 astronomers from Europe, the USA and Australia are members of the UK-led IPHAS consortium, which undertook the survey. To date, the survey includes some 200 million unique objects in the newly-released catalogue. This immense resource will foster studies that can be at once both comprehensive and subtle, of the stellar demographics of the Milky Way and of its three-dimensional structure.

The Southampton team, led by Dr Christian Knigge, oversaw the construction of the catalogue of hydrogen emitting stars, with much of the work being carried out by Dr Andrew Witham as part of his PhD thesis.

This list of nearly 5000 objects is already the longest single list of its kind. The distribution of these special objects, across the northern sky, traces 'hot spots' of recently formed stars in our Galaxy much more convincingly than has been possible hitherto.

Dr Knigge notes: "By providing astronomers with a convenient list of hydrogen emitting stars, we hope to make it much easier to find and study these intrinsically very rare objects."

IPHAS is embracing a recent change in the way astronomers share data. As well as being available through traditional web access it is also being published through a Virtual Observatory interface, where it can automatically be cross-referenced with other relevant data catalogues.

This initial data release is of observations of the Northern Plane of the Milky Way (the star filled section) that cover 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). The image resolution is high enough to permit the detection of individual stars exhibiting H-alpha emission, in addition to the diffuse gas that makes up the often-beautiful glowing nebulae that lower spatial resolution surveys have made known to us before.

The IPHAS survey will eventually be extended to cover the entire galactic plane of our galaxy, with a coverage approaching 4000 square degrees (for comparison, the moon on the sky as seen from Earth covers ~0.1 square degrees).

Notes for editors

  1. The paper reference is astro-ph/0712.0384 and the direct link to the abstract is (Gonzalez-Solares et al, 2007).
    Access is also available via the web at
    The paper presenting the catalogue of H-alpha emission line stars is available at (Witham et al, 2007).
  2. The INT/WFC Photometric H-alpha Survey of the Northern Galactic Plane (IPHAS) is an imaging survey being carried out in Halpha, Sloan r and i filters, with the Wide Field Camera (WFC) on the 2.5-metre Isaac Newton Telescope (INT) to a depth of r =20 (10 sigma). The survey is aimed at revealing large scale structure in our local galaxy, and also the properties of key early and late populations making up the Milky Way.


    The Virtual Observatory is an international initiative aimed at providing standard access to the world's global data resources. All systems conform to agreed interoperability standards defined by the International Virtual Observatory Alliance (

    A leading Virtual Observatory project is the UK's AstroGrid project ( The IPHAS data release has been made possible by utilising AstroGrid technology - this IPHAS IDR access work being one supported through an open AstroGrid Tools Call programme.

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