Density map of Milky Way shows 219 million stars

The data used to create the map were accrued over a period of ten years.
By Andrew McDonald | Sep 16, 2014
The disk of the Milky Way, a region which is the densest in our galaxy, extends over 100,000 light-years. So populated with stars, gas, and dust is the disk that the naked human eye is unable todiscern individual objects. If seen from Earth head-on, the disk only appears as an indistinct streak across the night sky.

Now, however, a new study has produced the most detailed map of the northern part of the Milky Way. According to a Royal Astronomical Society statement, the ten-year study, which was led by Geert Barentsen of the University of Hertfordshire, used a number of observations that were gathered by the Isaac Newton Telescope on La Palma in the Canary Islands. The newly compiled catalogue includes no fewer than 219 million stars.

The Isaac Newton Telescope's 2.5-meter mirror was able to distinguish and map all stars within the Milky Way that are greater than 20th magnitude in brightness; stars at the lowest end of that range are one million times fainter than the human eye can detect. The unprecedented catalogue of stars was then used to build the most detailed map of the Milky Way's disk, one which shows the variations in the distribution of stars across the disk.

In addition to releasing the catalogue and map, the researchers are making an extensive set of measurements available. These measurements have beenderived from two broad band filters that gathered visible red light, as well asa narrow band filter that gathered the brightest hydrogen emission line, H-alpha. H-alpha allowed for nebulae to be seen in detail in addition to stars. The use of redder wavelengths, rather than bluer ones, allowsmore detail to be revealed in the way of dust distributionaround the disk.

The new galactic catalogue was published on September 16 in the journal Monthly Notices of the Royal Astronomical Society.

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