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.

Screenshot 2019-05-13 at 16.04.47

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.

Screenshot 2019-05-13 at 16.13.00.png

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.

Screenshot 2019-05-13 at 16.05.51.png

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.

Screenshot 2019-05-13 at 16.06.33

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.

Screenshot 2019-05-13 at 16.06.49

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?

Island Universes – Inverness Science Festival


Face-on spiral galaxy NGC 6814

I’m looking forward to presenting another astronomy talk for the 2019 Inverness Science Festival.  Talk details below:

Astronomer Stephen Mackintosh from Highland Astronomy will take you on a journey through space and time, looking at the massive stellar structures that make up the observable universe – Galaxies.

How did we discover them, how many are there and what do they tell us about the immense scale and dynamics of the universe?

Plus tips and advice on observing galaxies and other faint deep sky objects for yourself.

Time:  7pm – 8pm,  8th May 2019

Venue:  Main Lecture Theatre, UHI Campus

Booking links:  Eventbrite


Wild Astronomy – Inverness Science Festival

milky way

I’ll be giving a public lecture at the Inverness Science Festival on May 11th 2018.  I’d love to use some images from local astro photographers, particularly night sky photos taken in the Highlands or north of Scotland.  If you’d like your images used I’ll fully credit you in the talk.  Please PM me for details.

Talk Title: Wild Astronomy

Description: The Highlands of Scotland have some of the darkest skies in Europe but how often do we escape our back gardens and ‘get out there’ to appreciate the night sky?

In this talk astronomer Stephen Mackintosh discusses what makes our Highland skies so special, the sights and objects we should look for, and how a backpack and a pair of binoculars is all you really need to open up the wonders of the night sky.

Time and Location:  May 11th, 7-8pm at University of the Highlands and Islands STEM Hub, An Lòchran, Inverness Campus, Inverness