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Milky Way

Milky Way & the ISS - (Ray Emery)
From Kielder (Ivor Trueman)
From Norfolk (Robin Jakeways)
From Norfolk (Robin Jakeways)
Galactic Centre
Galactic Centre
Galactic Centre


The Milky Way, in recent decades. has largely become hidden from view in the UK because of light pollution. It's estimated that about 85% of the UK population have never seen the our galaxy, which is a real shame. From a good 'dark skies' site, it is a truly fabulous experience.

The galaxy is known to be a barred-spiral with an estimated diameter of 150-200,000 light-years, containing an estimated 100-400 billion stars. Our Solar system sits about 27,000 light-years from the galactic centre (i.e. about halfway out out to the edge of the disc), in a minor spiral arm dubbed 'the Orion Arm' (aka the 'Local Arm'). Using radio telescopes and a variety of other techniques, the galactic structure has been modelled providing us with a face-on view, which we couldn't otherwise see.

Sitting as we do, in the galactic disc of the Milky Way, we can only see the galaxy from an edge on perspective lookng towards the centre, and from the UK can we only see roughly one 'half' of the Milky Way. Nearer the equator, both halves become visible:-

ESO - Milky Way
A 360-degree panorama view of the Milky Way from an assembled mosaic of photographs by ESO, the galactic centre is in the middle of the view, with galactic north up.

Towards the galactic centre, the Milky Way has a bulge that stretches out 10,000 light-years with tightly packed stars & a supermassive black hole at it's centre. The black hole, called 'Sagittarius A*', is a source of strong radio waves and has a mass approx 4 million × that of the Sun.

The stars and gases in the Milky Way rotate around its centre at approx 220 km/s and it takes the Sun 240 million years to complete one galactic orbit. From measurements of doppler shift, it's known that matter in the galaxy rotates at a constant rate, which indicates that there is a large amount of mass which has yet to be accounted for. This mysterious missing mass has been coined 'dark matter' because although it's gravitational effects are felt, it is not luminous.

For much more detailed info. see the Wikipedia entry.



Milky Way

Milkyway local arm midium

Image Credit: Xing-Wu Zheng & Mark Reid BeSSeL/NJU/CFA

For details of how this image was generated from radio telescope observations and other techniques, see https://astronomy.nju.edu.cn/xtzl/EN/index.html