Astronomers using data from the Isaac Newton Telescope on La Palma in the Canary Islands have assembled a catalogue of the visible part of the northern part of Milky Way Galaxy.
A density map of part of the Milky Way disk; the axes 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 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. Image credit: Hywel Farnhill / University of Hertfordshire.
From dark sky sites on Earth, the Milky Way appears as a glowing band stretching across the sky.
To astronomers, it is the disk of our own Galaxy, seen edge-on from our vantage point orbiting the Sun.
The disk contains the majority of the stars in the galaxy, including the Sun, and the densest concentrations of dust and gas.
The unaided human eye struggles to distinguish individual objects in this crowded region of the sky, but the Isaac Newton Telescope enabled Dr Geert Barentsen of the University of Hertfordshire and his colleagues to chart all stars brighter than 20th magnitude – or 1 million times fainter than can be seen with the human eye.
According to a paper published in the journal Monthly Notices of the Royal Astronomical Society (arXiv.org preprint), the catalogue contains information on 219 million detected objects, each of which is summarized in 99 different attributes.
Using the catalogue, the scientists have put together an extraordinarily detailed map of the disk of the Galaxy that shows how the density of stars varies.
The map illustrated here is derived from the longest wavelength band in which the darkening effect of the dust is moderated in a way that brings out more of its structural detail, compared to maps built at shorter wavelengths.
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Geert Barentsen et al. 2014. The second data release of the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS DR2). MNRAS 444 (4): 3230-3257; doi: 10.1093/mnras/stu1651
