IPHAS.MAP
A density map of part of the Milky Way disk, constructed from IPHAS data. This image contains 600 x 2400 independent data points, each of which represents the star count within 1 x 1 square arcminute cells (1 arcminute is 1/60th of a degree). The section shown features the edge of the Sagittarius spiral arm (near longitude 60 degrees) and the Cygnus-X molecular cloud complex (at around 80 degrees longitude). Hywel Farnhill, University of Hertfordshire

A ten-year programme has counted 219 million stars in the northern section of the Milky Way and placed the data on a density map, complete with latitude and longitude coordinates from the centre of the galaxy.

The team from University of Hertfordshire used the Isaac Newton Telescope on La Palma in the Canary Islands, according to the Royal Astronomical Society.

The disk of our galaxy which contains the majority of its stars stretches 100,000 light years. Discerning individual stars in this blurred patch in the sky is no job for the unaided eye but the 2.5 metre telescope picked the 219 million bright candidates and characterised some of them by more than 90 attributes.

By placing the stars on the map, astronomers get an idea of the density of stars in each region which in turn gives them insight into the structure of star, gas and dust.

The catalogue, IPHAS DR2, which is the second data release, provides free access to the measurements taken through two broad band filters capturing light at the red end of the visible spectrum, and in a narrow band capturing the brightest hydrogen emission line, H-alpha.

The inclusion of H-alpha also enables exquisite imaging of the nebulae (glowing clouds of gas) found in greatest number within the disk of the Milky Way.

The map clearly differentiates the dust-filled region (looking dark in the map) from bright regions packed with stars. The brighter the region, the more stars it contains.

The work appeared in the journal Monthly Notices of the Royal Astronomical Society.

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