ISF Talks – Island Universes

I’ve recently finished delivering two public lectures on Galaxies at this year’s Inverness Science Festival.

The theme of my talks was ‘Island Universes’, telling the tale of when and how we discovered our Milky Way isn’t the only galaxy, and how the teeming multitudes of spiral nebulae, hitherto believed to be collapsing dust clouds, were in fact individual galaxies.

The talk started with some observational astronomy, before discussing the great debate of 1920 between Harlow Shapley and Heber Curtis.  The main unresolved issue here was the distance to the spiral nebulae, particularly Andromeda, which was unknown.  This lead us into pulsating stars and the work of Henrietta Swan Leavitt, who systematically analysed and determined the period luminosity law for cepheid variable stars.

Finally we discussed Edwin Hubble and the ramifications of his observations on the red shift of distance galaxies, and how this has informed our current understanding of the history and future dynamics of the universe.

I’ll let some choice slides do the talking from here on.

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Our own galaxy ‘The Milky Way’ is big.  If you tried to travel from our position to the galactic nucleus at the speed of the Voyager spacecraft it would take you over 400 million years.

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A 1900s image of the Andromeda nebula.  Back then the consensus was these spirals were large collapsing dust clouds, a bit like the star forming Orion nebula.  The idea that they could be separate galaxies like our Milky Way seemed inconceivable, yet that’s where the evidence eventually lead in the 1920s.

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Determining the distance to spiral nebulae (as they were known pre 1900) required a new way of determining distance from so-called ‘standard candles’.  Leavitt’s law was invaluable when Hubble turned his attention to Andromeda in 1922.

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Hubble discovered the galaxies were all rushing away from us.  However this phenomena is actually a metric expansion of space itself, and therefore has no intrinsic centre.  Some of the most distant galaxies are receding away at faster than the speed of light – again due to the expansion of space itself, which has no speed limit imposed.

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There were lots of questions on M87, the giant elliptical galaxy whose black hole was recently imaged by the Event Horizon telescope.

Q&As are always lively after astronomy and space talks, and the younger audience members always surprise me with their amazing knowledge and frank curiosity.  Some choice sample from the two evenings below.  Answers on a postcard please .

1. Is the singularity at the end of a black hole the size of the Planck length?

2. If a giant hole suddenly appeared in the Earth how many Pluto’s could you fit inside it?

3. Do supermassive black holes continue to grow until they devour the host galaxy?

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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GSC On Tour

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Ross teaching us how to make a comet in a bin bag!

We had a great day of outdoor and indoor astronomy learning with our guests from Glasgow Science Centre on Saturday.

Ross and Andrew travelled all the way up to the A9 loaded with space and science kit to kick off this year’s first daytime event for the Star Stories programme.

Ross ran a fascinating hands-on Comet making workshop in one of the outdoor woodcraft sheds, demonstrating how Comets form and disintegrate as they travel round the Sun.

Meanwhile Andrew presented an indoor planetarium show using a projector and Stellarium software, taking audiences across the night sky and explaining some of the science and mythology surrounding the constellations.

Everyone seemed to have a great time and we’re looking forward to continuing the summer programme with our Summer Solstice event on the 21st June.  Please check my facebook page for booking details in the weeks ahead.

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Interactive exhibits kept the youngsters entertained between learning streams

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Outdoor astronomy learning

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Andrew’s star hopping presentation

 

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Urban Astronomy Inverness

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The formation of a young protostar following the collapse of a previously inert dust cloud

We had a great turnout for March’s Urban Astronomy session last week at the Sea Cadet’s Hall in Inverness.  The indoor presentation massively benefited from our new giant screen, expertly erected by Robbie (pictured below).  Here’s a selection of slides from my presentation on naked eye observing and the life of giant stars.

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Robbie putting the final touches to our new giant screen for indoor astronomy presentations and virtual sky guiding

Topics covered:

– Naked eye and binocular observing
– Satellites: Iridium Flares and ISS
– Colour, temperature and mass of stars
– The Hertzsprung-Russell diagram
– Protostar formation from dark nebulae
– Main sequence burning and final fate of stars
– White dwarfs, supernovae, neutron stars and black holes.

As ever there were some superb questions during and after the talk.  Stay tuned for upcoming events as myself and Caroline roll out the program.

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In the simplest terms stars behave like black body radiators with colour linked to their surface temperatures.

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The brightest stars in the night sky can be close – like Sirius – or giant stars very far away (eg. Betelgeuse, Rigel, Deneb).

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The HR diagram.  An elegant and reliable tool for describing the evolution of stars from main sequence burning into their final stages of life

Planetary Nebula

The term planetary nebula is highly erroneous, as these emission nebula have nothing whatsoever to do with planets.  Perhaps the most famous of these is the beautiful ring nebula in Lyra, not far from the brilliant star Vega, although many other planetary nebula are scattered around our night skies, and can be observed comfortably in larger telescopes.

The following video by ESA is a fantastic 3D model of the Ring nebula. In essence the ring nebula is the remnants of a dying Sun like star beyond its red giant phase. As the star enters its final stages its outer layers are shed in great expanding waves, and the residual hot white dwarf star at the centre ionises these gases into beautiful coloured shells.

This ionisation process is very similar to the mechanism that produces Earth based aurora. Electrons are recaptured within the host atoms (often hydrogen, helium, oxygen and nitrogen) and the drop to lower energy levels releases light of a specific frequency, governed by the simple equation we all learn in physics, E = hf.