Australian Sky & Telescope — January 01, 2018

12 AUSTRALIAN SKY & TELESCOPE January 2018

DISCOVERIES by David Ellyard

The Herschels and Uranus

The father discovered the planet, and his son named its moons.

F

or the Herschels, astronomy was

a business. William Herschel, his

sister Caroline, and his son John

all had brilliant astronomical careers,

spanning the 18th and 19th centuries.

For William and Caroline astronomy

was a second career, the first having

been music when they were residents

of the English city of Bath and leading

lights in the local musical community.

The planet Uranus was another

connection between father and son.

William had discovered the planet, the

first to be identified since antiquity,

through his interest in double stars.

(Hewasoneofthefirsttosuggestthat

manyofthepairsofstarsthatappeared

tobeclosetogetherintheskywerein

factgravitationallylinkedandorbited

each other). During these observations,

Herschelsawa‘star’withavisible

disc, and wondered if his self-designed

andconstructedtelescopewasinfact

powerful enough to ‘resolve’ the object.

Laterobservationsshowedthatthe

‘star’movedagainstthebackgroundof

fainterstarsandsohadtobeaplanet.

Herschel named his discovery after

the English king George III, calling it

‘George’sstar(siderius Georgiiin Latin),

much as Galileo had done in naming

hisnewlydiscoveredmoonsofJupiter

after the Medicis who ruled Florence.

It was a cunning move. The King was

pleased; he made Herschel the ‘King’s

Astronomer’ (as distinct from

the Astronomer Royal) and

made money available for

the building of new

telescopes, so setting

Herschel on his

well-known ‘bigger

is better’ crusade.

He was also made

a Fellow of the

Royal Society. He

had gained the

kind of fame his

music had never

delivered.

In France, the

new planet was known

simply asHerschelsince

the revolutionary climate there

wouldnottolerateanyreferencetoa

king. The nameUranuswas not settled

upon until the 1850s, by taking account

ofthegenealogyoftheGreekgods.As

Saturn had been the father of Jupiter, so

Uranus was the father of Saturn.

We are revisiting all this this month

because on January 11, 1787, Herschel

found two moons circling his newly

discovered planet. These languished

unnamed for more than 60 years, until

fellow English astronomer William

Lassell(whohadfirstsightedNeptune’s

biggestmoon,Triton)foundtwo

more of them. It was time to name

the growing brood. Lassell turned

to Herschel’s son John, who by then

had taken a leading place in British

astronomy.

JohnHerschelbrokeawayfromthe

traditionofusingGreekmythological

names for astronomical objects,

turninginsteadtoEnglishliterature,

especially to Shakespeare’s playA

Midsummer Night’s Dreamand the

poem The Rape of the Lock by Alexander

Pope. So the two moons his father

found became the fairy king and

queen — Titania and Oberon from

theDream — and Lassell’s pair

were henceforth the sprites

Umbriel and Ariel from

the Lock, though Ariel

also is a character

in The Tempest by

Shakespeare. The

next new Uranian

moon wasn’t found

until 1948, and

that was dubbed

Miranda (f rom The

Tempest).

Thanks to the

Voyager probes and

dvanced telescopes on

Earth, we now know that

Uranus has 27 moons, all with

names drawn from Shakespeare and

Pope. John Herschel would have been

surprised to see how far his naming

strategy has gone.

As a postscript, may I say that

William Lassell is an interesting

character. Like so many of the British

astronomers of the time he was an

amateur, turning to astronomy after

having made a fortune elsewhere —

after all, there were very few paid

positions in astronomy at that time.

In Lassell’s case the money came from

brewing. He continued Herschel’s drive

to build bigger telescopes, and made his

large telescopes much easier to use and

guidebyinventing the equatorial mount.

Like John Herschel, he also sought

darker and clearer skies to enhance his

observations. He took his telescopes to

Malta; Herschel went to South Africa.

■DAVID ELLYARD presented SkyWatch

on ABC TV. His StarWatch StarWheel

sold over 100,000 copies.

John Herschel broke with tradition

when naming Uranus’ moons.

This portrait by Edward Alfred

Chalon dates from 1829.

S William Herschel named it ‘George’s

star,’ but the planet eventually became

known as Uranus.