Spotting the Zodiac Signs

This piece was written by a Volunteer Tour Guide, Elaine, and discusses one of the interesting details in the Painted Hall.

Header image ©Paul Rudkin

Spotting the Zodiac Signs

What’s your star sign? Are you one of the favoured ones in the Painted Hall whose symbols feature twice? Once among the twelve along the Central Oval balcony and again in the six in gold on the Proscenium Arch. Have you heard this explanation for why these particular six were chosen?

“These are the signs visible in the Northern Hemisphere so would have been more familiar to the pensioners.”

Leaving aside the fact that many of the pensioners would have been very familiar with Southern Hemisphere skies, you might have wondered how the ancients ever knew about Pisces, Aquarius, Capricorn, Sagittarius, Scorpio and Libra, if they couldn’t see them. Our astrological signs come to us from the Babylonians via the Greeks – both firmly in the Northern Hemisphere.

What are the zodiac signs?

Our planet orbits the sun in 365.25 days (check Copernicus showing us his theory at the east end of the Lower Hall ceiling). Imagine a straight line drawn from the Earth to the sun and beyond to the distant stars. As the Earth makes its yearly journey that line will trace out a circle. That circle, and the stars that lie on or near it, is the Zodiac.

Astronomers in Ancient Babylonia divided the annual circle into 12 equal sections and named them after the most prominent constellation (dot-to-dot patterns) visible in each section. The 12 signs that we’re familiar with today came into use around 2,000 years ago as Ancient Greek astronomers took inspiration from their predecessors. The word ‘zodiac’ comes from the Greek meaning ‘circle of animals’.

How have the zodiac signs changed over time?

Perhaps you think Pisces, Aquarius and Co were visible from the Northern Hemisphere in 1500 BCE but not in 1700 CE? Not too silly. Things have actually changed a bit – the Earth’s daily rotation is like a wobbly spinning top. This is called procession of the equinoxes. Each wobble takes 26,000 years so over a few thousand years our view of the stars has changed a bit. But the only significant change it has made to the star signs is that they are all now out by about 3 weeks.

If you were born yesterday you are Taurus in theory but in practice the sun is still in Aries. That means that if we could see the stars during the day, say during a total solar eclipse, the sun at that moment would be framed by the constellation Aries. But you can’t see the stars during the day, which means we can’t see Aries at the moment. You have to wait a month or so until the Earth has travelled along its orbit so that the sun is “in” Taurus. Then if you get up before dawn you will see Aries rising before the sun in the eastern sky. Or if you wait six months till October, when the Earth is on the opposite side of its orbit, Aries will rise in the east in the evening and be visible in the night sky till dawn.

So why just six signs on the Proscenium Arch?

Well, they are the first six. Facing the Upper Hall if you start from the right, Aries is first. The New Year started in Spring until relatively recently. Secondly, it is true that because of the Earth’s tilted axis of spin these six Zodiac signs are higher in the Northern Hemisphere night sky when they are visible. And of course they are mostly visible in winter when there is more darkness for star-gazing. But I suspect that Robert Jones who carved them, along with the magnificent coat of arms above them, decided that as a consecutive group they would look the best – bolder shapes, easily recognisable (unlike some of Thornhill’s signs around the Central Oval) and less complicated. Or it is possible that he intended to include the other six somewhere else in the hall and never did for whatever reason.

How can I see the zodiac tonight?

Finally for any would be astronomers, look south-west around 8pm on a clear evening around now, in April, and you will see the zodiac constellations, not overhead (unless you are somewhere very exotic!) but definitely forming a low arc across the night sky, left to right, Virgo to Aries, just like on the Proscenium Arch.