Monday, 14 October 2013

Andromeda Reloaded

It's getting to that time of year again when the 'Clash of the Titans' constellations fill the eastern night's sky; Pegasus, Perseus, Cassiopeia and of course Andromeda. Last night was a beautifully clear one and I managed to get a marginally better view of the Andromeda galaxy than I did last year before moving on to an utterly fruitless attempt to see Neptune through my plucky little telescope. So I thought I would repost this blog from last year on the history of its observation.

Andromeda Galaxy as photographed by  Isaac Roberts 1888

Winter is coming as they say in Westeros and with the return of dark evenings I found myself on Saturday night scurrying back and forth from the garden where the trusty scope had been trained on the patch of sky above the neighbour’s fence, frowning at the scudding clouds.

At last the sky cleared at least for a while and I cranked, swivelled and twiddled my way through the rising constellation of Andromeda until finally I beheld a cloud-like entity amongst the stars. Having repeatedly checked that the object of interest was neither a rogue regular cloud drifting across my field of view nor a greasy spot on the eyepiece, I pronounced myself satisfied that I had indeed eyeballed the Andromeda galaxy and wished as usual that I had invested in a larger telescope. Even so, it was still another tottering step forward in my astronomical adventures and one has to start somewhere. 
Just then the clouds closed in once more and ended my observations for the evening and I retired to the comfort of the living room. Whenever I feel like grumbling about the limitations of my present technology I remind myself that the pioneers of astronomy would have killed to have a telescope as good my much disparaged 76mm and that they made incredible discoveries and deductions using far more primitive instruments.

The first man known to have observed the Andromeda galaxy did not even have a telescope. Abd al-Rahman al-Sufi, known in the west as Azophi, was a Persian astronomer living in Isfahan during the Tenth Century. Having studied and augmented the works of Ptolemy, Al Sufi compiled his own Book of Fixed Stars, which was completed in 962 AD. Within it he describes a small cloud located within the constellation of Andromeda.

The Constellation of Andromeda as pictured in the
Bodleian Library's copy of Al Sufi's Book of Fixed Stars
It was not until 1612 that the Andromeda galaxy was observed by a European astronomer; Simon Marius, who is best known for infuriating Galileo by claiming to have observed the moons of Jupiter prior to Galileo’s own discovery which he announced in his seminal Sidereus Nuncius of 1610. Marius’ claim to have been the first was largely discredited but his re-discovery of Andromeda stands as his signal achievement.

Andromeda, designated M31, is flanked by two satellite dwarf galaxies. The first of these M32 was discovered by French astronomer Guillaume le Gentil , who was perhaps the unluckiest man in the history of astronomy.

Le Gentil set out in 1760 to observe the 1761 transit of Venus from Pondicherry, India. Prevented from reaching his destination by the outbreak of war between England and France, Le Gentil was at sea at the time of the transit and his efforts to observe it from the deck of the ship in rough weather were hopeless. Undeterred, he determined to wait for the next transit in eight years’ time. He spent the intervening years fruitfully, travelling the Indian Ocean on mapmaking expeditions, carrying out astronomical observations and recording details of flora and fauna. When the time came around for the next transit, Le Gentil returned to Pondicherry only to be thwarted once more by storm clouds. His frustration can only be imagined. When at last he returned to France he found that he had been given up for dead and his relatives were squabbling over his estate.

That is the fate that often awaits astronomers. I had gone more than ten thousand leagues; it seemed that I had crossed such a great expanse of seas, exiling myself from my native land, only to be the spectator of a fatal cloud which came to place itself before the Sun at the precise moment of my observation, to carry off from me the fruits of my pains and of my fatigue.
Guillaume le Gentil 1769

Caroline Herschel
The second satellite galaxy of Andromeda, designated M110, was discovered in 1783 by Caroline Herschel, sister of William, who through the course of assisting her more celebrated brother became an accomplished astronomer in her own right. Caroline blazed a trail by becoming the first woman to receive a state salary for undertaking scientific endeavours.  As she moved from under her brother’s shadow and began to make her own independent discoveries Caroline identified eight new comets as well as the galaxy M110. Following her brother’s death Caroline, who never married, returned to Germany and lived to the ripe old age of 97, receiving a gold medal from the King of Prussia for her scientific efforts.

I was interested to learn that the reason all deep sky objects are given a number with a prefix M, is due to one Charles Messier - 1730-1817 - another good innings! Messier was a prodigious hunter of comets, indeed he discovered thirteen of the things and to aid fellow comet hunters he helpfully created a catalogue of nebulous objects in the night's sky. It is for Messier therefore that M31 and all other nebulous celestial phenomena are so named. For his achievements Messier received the Legion d'Honeur. He is buried in Pere Lachaise cemetery.

Charles Messier

Andromeda’s beautiful spiral structure was first elucidated by Welsh astrophotography pioneer Isaac Roberts whose magnificent long exposure photograph appears at the top of this post. It was taken in 1888 by mounting a photographic plate in the prime focus position within his twenty inch telescope housed in a purpose built observatory at the bottom of his garden.

Roberts had shown the  Andromeda galaxy  in detail but it was still thought to be a nebula within the Milky Way rather than an entirely separate and far more distant galaxy. The debate was soon raging however as to whether  our own galaxy comprised the universe entire or whether it was just one of many galaxies in an infinitely larger ‘island universe’. In 1924 Edwin Hubble, by observing the Andromeda Galaxy through the 100 inch Hooker telescope at Mount Wilson Observatory, discovered the means to settle the argument once and for all.
The Hooker Telescope under construction

Hubble identified the presence of Cepheid variable stars within the Andromeda Galaxy, whose brightness varies over time in regular pulses. By measuring their pulsation periods, Hubble was able to calculate their luminosity since the two are relative. By comparing the observed and expected luminosities of the stars, Hubble was able to deduce their distance from the earth at some 900,000 light years. He thus demonstrated that they were so distant that they must lie outside of the Milky Way, the size of which had already been estimated at 100,000 light years.  Hubble had proved that the universe was comprised of many galaxies and was a bigger place than anyone had previously imagined. Indeed he underestimated in his calculations, for Andromeda is now known to be two million light years away.

And when I think about that I am definitely impressed to have seen it at all!

Al Sufi's Book of Fixed Stars
The ordeal of Guillaume le Gentil
Edwin Hubble
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