Why Venus is the morning or evening star…

Morning and Evening Star by Alphonse Mucha, 1902

I find it hard to believe that I have only just put two and two together and worked out why Venus is always the morning or evening star!

I expect you know already, but if you think about it, as Venus is closer to the sun than we are, it’s always going to be seen as in the sun’s general direction. It’s never going to be back “over there”, outside our Earth orbit. In fact its farthest possible distance from the sun in the sky is about 47 degrees.

After the moon, Venus is the brightest object in the night sky. Of course it’s a planet, not a star, but the ancients didn’t always differentiate. I particularly like Alphonse Mucha’s depictions of Venus as evening and morning star (pictured above).

The planet Mercury is also an evening and morning star, but not nearly so obvious as it is much smaller than Venus and much closer to the sun. As we are the “third rock from the sun”, we view all the other planets as “out there” beyond us.

Venus grows so bright when it is on our side of the sun that it can often be seen in daylight. I realise now that I have seen it in daylight in the last year and been frightened, as I didn’t understand! That UFO feeling…

John Pratt’s diagram – Earth is at the bottom, the sun in the middle and the position of Venus in the numbered circles

There is a great deal about the orbit of Venus on John Pratt’s web page – follow this link. On his diagram above, Venus will appear to us as the evening star between points 3 and 5 and morning star between 6 and 2.

Venus is in the news this month as it experiences what to us is at best a twice-in-a-lifetime phenomenon – the transit of Venus across the face of the sun, as seen from Earth.

A lovely photograph by David Cortner of the last transit of Venus, in June 2004, featured on the Astronomy Picture of the Day

Venus goes around the sun in 224.65 days, while Earth orbits in 365.25 days (our year). So it should come between us and the sun much more often – except that our orbits aren’t in the same plane, so transits, when Venus appears to cross the sun’s face, happen much less often. Transits are like eclipses, except Venus is too small to block out much of the sun.

According to Wikipedia, Transits of Venus occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years.

I can’t believe how lacking in curiosity I was when I saw the last transit, in 2004. I wasn’t blogging or Tweeting at the time, so clearly saw no reason to research what was going on very much. However, I DID observe it, and wrote about it in my diary:

Tuesday, June 8, 2004

I watched the Transit of Venus through binocular projection – Venus was at the top, going from right to left, not bottom as in images on net and TV (inverted because of binoculars?). I did it sitting on the bedroom floor, pointing the binoculars through the window and focussing on a sheet of A4 paper. Great. I did this a couple of times to see the movement, between 7.30 and 8.30am.

William Crabtree watching the Transit of Venus AD 1639 by Ford Madox Brown, a mural at Manchester Town Hall

I am rather pleased that a very similar method to mine, but with a telescope, was used by both Jeremiah Horrocks and William Crabtree to observe the transit in 1639.

Sadly on the morning of June 6 this year I doubt if I will make such an observation, as the transit will be over at 5.55am our UK time, which I think will be before the sun rises over my city horizon. And I expect it will be cloudy anyway…

After that the next transit isn’t until 2117 and it will be the first of a pair of transits around December 7, eight years apart.

Historically, the 2004/2012 transits are the fourth pair to have been observed scientifically.

In 1627, Johannes Kepler was the first person to predict a transit of Venus, for 1631. But sadly he hadn’t realised in time that it wouldn’t be visible from most of Europe, so no arrangements were made to view it.

There was better luck in 1639, when Jeremiah Horrocks corrected Kepler’s sums, worked out the eight-year-gap aspect and predicted the transit. He observed it in Much Hoole, near Preston, while his friend William Crabtree (pictured earlier) viewed it in Broughton near Manchester.

A book on Jeremiah Horrocks came out to coincide with the 2004 transit and I picked it up but have not yet read it. Maybe now I will…

The cover of my copy of The Transit of Venus, by Peter Aughton, published to coincide with the 2004 transit

In 1761 several expeditions were made to various parts of the world to observe the transit of Venus in order to follow through on an idea of Edmund Halley (who had died in 1742) that the “parallax method” could be used to work out the distance between the Earth and the sun.

The method works in more or less the same way as our binocular vision – we judge something’s distance by comparing the way it looks from both the left eye and the right eye.

By the way, one of the expeditions in 1761 was Captain Cook‘s first voyage, in which he viewed the transit from Tahiti.

In 1874 and 1882 more expeditions were sent out and more parallax observations made, nailing down the distance from the Earth to the sun to around 150 million kilometres.

Finally, there is a connection between Venus and another of my
long-standing interests – the Aztec god Quetzalcoatl (“the feathered serpent”).

Quetzalcoatl as depicted in the Codex Borbonicus

John Pratt has a very good explanation of how the story of Quetzalcoatl and observations of Venus are parallel.

When Venus first rises in the west as an evening star it could represent the “birth” of Quetzalcoatl. It gets brighter every day like a child growing up and stays at its brightest for about a month.

Then it seems to “die” for eight days – equivalent to Quetzalcoatl’s time in the underworld – and finally returns in all its glory as morning star.

Those eight days are between the points 5 and 6 on John Pratt’s diagram. When Venus disappears on the far side of its orbit, between points 2 and 3, we miss it for 50 days.

My apologies that this post is probably a bit boring, but I just had to get some thoughts down on this one – as I won’t have a chance again in this lifetime.

And don’t forget – never look directly at the bright sun with the naked eye or through a telescope or binoculars or in a mirror! Your vision is precious.

For more about me and Mucha, see my post Every poster tells a story…

Advertisements