219 million stars: a detailed catalogue of the visible Milky Way

A density map of part of the Milky Way disk, constructed from IPHAS data. The scales show galactic latitude and longitude, coordinates that relate to the position of the centre of the galaxy. The mapped data are the counts of stars detected in i, the longer (redder) wavelength broad band of the survey, down to a faint limit of 19th magnitude. Although this is just a small section of the full map, it portrays in exquisite detail the complex patterns of obscuration due to interstellar dust. 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).  At the level of the original exposed images, each cell is itself made up of 32000 pixels. The typical effective angular resolution of the data is close to 1 arcsecond (1/3600th of a degree or about 10 original image pixels). 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). Both of these appear as regions of reduced star counts due to the obscuring effect of higher dust concentrations. Credit: The stellar density map has been produced by Hywel Farnhill as part of his PhD project at the University of Hertfordshire.

A new catalogue of the visible part of the northern part of our home Galaxy, the Milky Way, includes no fewer than 219 million stars. Geert Barentsen of the University of Hertfordshire led a team who assembled the catalogue in a ten year programme using the Isaac Newton Telescope (INT) on La Palma in the Canary Islands. Their work appears today in the journal Monthly Notices of the Royal Astronomical Society. For more info click here.