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.

The Andromeda Galaxy

Many people are unaware that you can observe a totally independent galaxy, outside our own Milky Way, with a basic pair of binoculars, or even the naked eye with good seeing. Here’s how to find Andromeda, our brightest and closest large galactic neighbour.

Finding it

Mars is well placed high and bright in the SW at the moment to help you find Andromeda. From Mars find the four stars marking the great square of Pegasus and then star hop to its rough location using my guide below. Scan this region of sky with binoculars and you should eventually see a faint glow of diffuse light. That’s Andromeda.

What you’re seeing

The Andromeda galaxy is our nearest galactic neighbour at around 2.5 million light years away. Which means when you see it, the light reaching you left Andromeda millions of years ago, a time long before human beings dominated our planet. How is it we can see Andromeda at this stupefying distance when we can only see stars within a few thousand light years? The reason is size and composition. Andromeda, just like our own Milky Way galaxy, is a vast spiral storm of stars, over 100,000 light years in diameter. The glow of light you see is from an accumulation of over one trillion stars.

Milky Way Images

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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.  www.callanishdigitaldesign.com

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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 Summer Milky Way

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The summer aspect of the Milky Way, the great river of starlight marking our home galaxy.  A giant stellar disk containing 100s of billions of stars.  Photograph by Christopher Cogan, taken near Muie in east Sutherland, Scottish Highlands

Late summer is prime time for observing the Milky Way, and esp. catching the bright core visible near the southern horizon after dark. This bright area marks the central nucleus of our galaxy, some 30,000 light years away..

The Milky Way currently runs between Saturn and Jupiter, both low on the southern horizon, and intersects the three bright stars of the Summer Triangle asterism (Vega, Deneb and Altair). From south It runs overhead and terminates close to the constellation Perseus in the north East.

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For the best views you’ll want to get away from urban light pollution, ideally somewhere fairly rural. Let your eyes dark adapt for at least 15 minutes to give yourself the best possible views.

Clear skies.

Stargazing at Scapa Festival 2019

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The milky way from the grounds of the Arkinglas Estate, Loch Fyne

I had another great time hosting outdoor astronomy and stargazing workshops at this years Scapa festival, held on 3-5th May near the shores of Loch Fyne at the Arkinglas Estate.

It was very busy, especially Friday evening when clear skies brought many folk streaming down into the gardens in anticipation of stargazing close to the shoreline.

As it happened we hit some cloud just as I was about to kick off, prompting a quick jump over to my backup projector and screen.  I was then able to deliver a 30 minute talk with Q&A, discussing things like the colour, temperature, distance of stars, the Milky Way, other galaxies, shooting stars and large impactors.  As ever the questions were fascinating.

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A passing satellite

Just as the talk wrapped up skies cleared and we were stargazing from the estate grounds.  Plenty of constellations and bright stars began appearing, and conditions improved further when a second group arrived to join in.

Similar conditions prevailed on the Saturday, when skies once again cleared up after my talk, allowing us to observe with the large case of binoculars I always bring to star parties.

Later on I was able to photograph some lovely shots of the Milky Way from the estate grounds, with the band of our galaxy sitting low and clear on the northern horizon.

Feedback has been great on the guiding so far, and I’m looking forward to getting involved again next year.

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Galaxy Photobomb

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When an entire galaxy (faintly) photobombs your night sky picture!

I was sorting out some of my recent images from the west coast and spotted the Andromeda galaxy. That’s my camper van at the bottom looking west over the sea near Arasaig. Sky glow is from the recently set Sun.

That fuzzy elongated smudge I’ve highlighted is the combined light from over 400 billion stars. A completely separate island universe over 2.5 million light years away.

Here’s a few other pictures from this excursion posted below.

 

Stargazing at Roseisle

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Starry skies over the Moray coast

Amidst a very busy schedule last month I managed to head out to Roseisle (along the Moray coast) for some observing and a wild camp.  My original mission was to try and catch a geomagnetic storm predicted by the MET office space weather forecasts.  As it happened the promised aurora didn’t arrive but I did manage to get some photos of the starry skies that opened up on Saturday night, starting with the International Space Station.

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Not the most fantastic ISS shot but I only had about 20 seconds to set up after running down the dunes to capture the pass!.  The station is actually travelling from west to east here, towards Sirius (bright star on left)

From there I took a number of pictures hoping to capture some aurora, but instead imaging the crisp starry skies.  I’ll let the photos do the talking from here – please read the caption notes.

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This image of the Plough (minus Alkaid) was snapped while I was still under the trees, on my approach to the beach.  You can clearly see the naked eye double star Mizar-Alcor at the bottom of the image.  The main stars in the Plough are roughly 100 lights years away.  Our Sun would not be visible naked eye if placed this far away which tells us something about the scale and luminosity of these titan stars.

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Looking north towards Burghead where I hoped to capture some aurora.  Instead I picked up the rich star fields within the Milky Way near Cassiopeia.

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One of many passing satellites.

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An interesting shot looking north west.  The bright white light is the Portmahomack lighthouse and the orange light pollution on the right is likely from Helmsdale.  Perhaps the most interesting feature in this photo is the faint smudge of light in the top left.  That’s the Andromeda galaxy – a separate spiral galaxy (larger than our Milky Way) over 2.5 million light years away.