Using the Twelve Days of Christmas as a foundation, Paul Hill’s talk was a seasonal, light and light-hearted ramble through various things astronomical. And, typical of Paul, he threw up a number
of little jewels of information that I’m sure will come in useful at the next Pub Quiz!
He started with the Astronomical Unit as Nº 1, pointing out that Aristarchus had a go at measuring this over 2000 years ago – but getting it wrong by a factor of 1000 (he didn’t appreciate the size of the Sun). It wasn’t till the Venus transits of the Sun in 1761 and 1769 that more accurate measurements were made. Paul made novel use of a toilet roll to illustrate the size of the solar system in AU’s!
Nº 2 was the forthcoming conjunction of Saturn and Jupiter – watch out for it at its closest since the year 1226 on 21st December 2020!
Nº 3 was Syzygy – strange word! – a “Conjunction Plus” if you will, involving three bodies, most familiar perhaps between the Sun, the Earth and the Moon.
Four Giant Telescopes, on-line soon, came next. Starting with the smallest with “only” an 8.4 metre mirror, the Vera C Ruben telescope, and equipped with a 3.2 Giga-pixel CCD camera! The largest new scope will be the European Southern Observatory’s Extremely Large Telescope with its 39.3 metre mirror – apparently 40 metres was the original plan, but reducing it by 70 cm took half a billion dollars off the bill!
Then the five classical planets of our solar system and the names they used to be known as by the Romans and Greeks. The Group VI stars on the Hertzsprung–Russell diagram formed Nº 6 – the Sub-Dwarf Stars. These are metal poor stars containing only Hydrogen and Helium which reduce their opacity and radiation pressure making them 2 magnitudes dimmer than ordinary dwarfs of the same size.
What could Nº 7 be? Well, the Pleiades (M45), obviously! The Seven Sisters. Because they are relatively close to us and all of a similar type, this cluster can be used as a stellar calibration device.
Nº 8 was Analemma – another strange word – and it describes the motion of the Sun in the sky as seen from a fixed location on Earth at the same mean solar time, so that position varies over the course of a year. Turns out to be a figure of eight.
The Search for Planet X came ninth. Not that we should expect to ever find it, but you could look in Taurus if you really want to because, if it exists, that’s possibly where it is.
Pioneer 10 came next, humankind’s first spacecraft to venture outside the Solar System. Launched in 1972, and out of touch at 800 AU’s in 2003, it’s a bit of a slow coach by modern standards. Voyager 1 has already overtaken it, Voyager 2 will do so soon, and so will New Horizons. In fact, only in 90,000 years’ time it will pass its first star, somewhere near Aldebaran!
The 11-year Sun cycle came next, attracting a number of questions in the discussion that followed Paul’s talk. We’ve seen a minimum period of activity over the last few years, but we can look for much higher levels in the period 2023 – 2026. Time to start saving for that Solar scope, then!
Finally, Nº 12 – the twelve signs of the Zodiac. The star signs we have today are actually wrong because since the Babylonians drew them up, the Earth has wobbled on its axis (precession). One’s birth sign should be the constellation where the Sun was when you were born. For example, if you were born between February 16th and March 11th, then the Sun is in Aquarius. So, there’s me thinking I was a Pisces and it turns out I’m an Aquarian! Not that this little nugget will help me much at the next Pub Quiz, I suppose
Sandy Giles