How Astronomers use the EM Spectrum

This is Bode’s galaxy (M81), an easily accessible island universe in Ursa Major that’s visible all year round from mid to high northern latitudes. It contains approximately 250 billion stars.

It lies over 10 million light years away and has a relatively close galactic companion – the M82 Cigar galaxy. Both of these galaxies can be framed in a low power telescopic eyepiece, and you can even see them very faintly in binoculars if your skies are suitably dark.

I thought I’d use this galaxy to highlight how astronomers use the full electromagnetic spectrum of light to study galaxies and their evolution. Pictured below, therefore, are images of M81 viewed in different wavelengths of light – from X-rays to radio waves (spanning short to long wavelengths). I’ve provided a very brief description of some of the galactic features revealed by each band of light.

X-rays: a central bright patch is revealed, suggestive of a supermassive black hole within the galactic nucleus. The other bright patches correspond to X-ray binary systems.

Ultraviolet: highlights young hot stars and therefore areas of active star formation within the spiral arms of the galaxy.

Optical and Infrared: Shows the bulk of the stellar population and areas of obscuring dust and nebulosity that will seed ongoing star formation.

Radio: Reveals supernova remnants and large H2 regions of ionised gas in the vicinity of very active stellar populations.

As humans our eyes have evolved to see a very narrow band of the full EM spectrum. This evolution is tied to the fact our particular star (the Sun) releases its peak energy in these wavelengths. I always like to imagine how other species, perhaps evolving next to giant sources of x-rays, might have sensory apparatus totally blind to visible light.

New Information on Betelgeuse

Betelgeuse, shown here as the top left star in the shoulder of Orion

Some interesting new information has emerged on Betelgeuse, the red supergiant that marks the left ‘armpit’ of Orion the Hunter.

In summary:

1. It’s still burning Helium in its core so unlikely to go supernova until around 100,000 years.

2. It’s not as massive as previously thought. Earlier studies had shown its radius would extend to the orbit ofJupiter if placed in our solar system. This new data suggests its real radius is 60% of this.

3. It’s closer to Earth than previously measured, at 530 light years. This is 25% closer than we previously thought.

New data published in the Astrophysical Journal. Further reading here.

Watch a Supernova Explosion in a Distant Galaxy


See a supernova explosion in a distant galaxy over 50 million light years away.

Berto Monard witnessed Supernova 2015F in spiral galaxy NGC 2442 in March 2015, although the actual event happened 50 million years ago, long before human beings inhabited planet Earth.

Supernovae like this produce so much light energy they can briefly out shine the accumulated light from the entire galaxy. For this reason they can be witnessed even with moderately sized back garden telescopes, if you’re lucky enough to be pointing in the right direction at the right time!

Video Credit & Copyright: Changsu Choi & Myungshin Im (Seoul National University)
Source: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)

Milky Way Images


The Milky Way over the Callanish Stones on the Isle of Lewis.  Jupiter and Saturn can be seen in this shot low above the horizon. By Emma Rennie of Callanish Digital Design.


Another stunning Milky Way shot by Christopher Cogan taken from Muie in Sutherland in the far north of Scotland.

Two stunning Milky Way images taken last night from the Scottish Highlands (and Islands). Both show the bright region of the Milky Way in the vicinity of the Summer Triangle, looking south.

If you imagine our Milky Way as a vast disk of stars, these views are peering further ‘into’ the disk, where the density of stars and stellar matter is greater, and hence brighter. Contrast this with the fainter regions we see in Winter near Orion, when we peer ‘out’ of the galactic disk.

The dark lanes you can see are part of the Cygnus Rift – a region containing vast clouds of dust that obscure some of the light from the billions of stars in the background.

With the Moon well out of the way and proper darkness returning late at night, now is a great time to go out and see the Milky Way for yourself.

The Cat’s Eye Halo


Image Credit: R. Corradi, Nordic Optical Telescope

I recently stumbled across this stunning image of the famous Cat’s Eye nebula. It’s a false colour enhancement showing the extended ejecta from the dying star, imaged by the Nordic Optical Telescope on the Canary islands..

The cat’s eye is dubbed a ‘planetary nebula’. An erroneous label as this has nothing to do with planets whatsoever. Rather these nebulae are the beautiful symmetries left behind when stars of similar mass to our Sun enter their final gasps of life. Before collapsing down to a white dwarf (a compact star held in place by electron pressure), the star sheds its atmosphere is great puffs, producing these ghostly but beautiful clouds of ionised gas.

I made a video about Planetary nebulae you can watch here:

The outer gaseous tendrils seen in this image extend almost 3 light years across and probably represent earlier and more transient episodes of stellar influenza, before the star began its collapse in earnest.

Image Credit: R. Corradi, Nordic Optical Telescope

An Alien Solar System


A direct image of an alien solar system orbiting a Sun like star, over 300 light years away!

I remember growing up in the 1980s hearing about the ‘high probability’ that other stars had orbiting planets, but there was very little evidence then, only some tantalising hints from the gravitational wobbles observed from specific stars.

Since then thousands of new exoplanets have been confirmed using the transit and radial velocity detection methods. I wrote a blog article about this a while back.

These methods are indirect ways of determining the existence of planets, and it’s very rare to actually be able to ‘see’ the planets themselves.

This image is therefore pretty incredible and for me suddenly normalises the idea that these star systems are real places we could, theoretically at least, visit in the distant future.

The image was captured by the European Southern Observatories Very Large Telescope and shows a young Sun like star (only 17 million years old) with two clearly defined giant planets in orbit. (The dots of light closer to the star are background stars and therefore not part of this particular planetary system)

These planets orbit the star at 160 and 320AU (1 AU is the Earth to Sun distance) so they’re much further away from the star than any planet in our solar system.


‘Gamification’ – Stellar Evolver

An example of gamification in one of my recent projects called Stellar Evolver (with audio voiceover). This is a fully VR ready experience and will enable players to interact with and watch the evolution of star systems using the visceral mechanics and feedback of a 3D based shooter.

Stellar systems can evolve from simple proto-planets up to red dwarfs and larger giant stars, eventually culminating in the formation of neutron stars and black holes.

Clearly the overall dynamics, scale and time is being exaggerated here for playability. I hope to demonstrate a working multiplayer prototype at the 2021 Hebridean Dark Sky Festival.

Developed by Mackintosh Modelling & Data Simulations