Postcards from the edge

After its recent safe arrival on Mars, the Curiosity lander has been sending gorgeous postcards home to make us wish we were there. I love the colours in this landscape: from taupe to turquoise. I can feel some inspiration for interplanetary craft (projects). Image credit: NASA/JPL-Caltech/MSSS

Orreries

I've always wanted an orrery. Perhaps not exactly like Aughra's orrery in The Dark Crystal (for a start, where would I put it?) but I'm fascinated by the idea of a mechanical representation of celestial motion.

Did you know: 

• That it was called an orrery after the Earl of Orrery commissioned a mechanical planetarium as a gift for his son in the early 18th century?
• That you can make your own orrery from such mundane materials as Meccano and LEGO?
• That you can buy your own working orrery, designed and made by Brian Greig, who created the gorgeous Tellurion at Sydney Observatory?

Something remarkable

Every so often, the planet Venus does something remarkable. Its orbit brings it to a point directly between the Sun and the Earth, where it appears to us as a black dot moving across the bright disc of the Sun. This transit of Venus is rare, occurring in pairs eight years apart and then not for more than a hundred years; it has fascinated astronomers for centuries.

Nick Lomb, Transit of Venus: 1631 to the present (NewSouth Publishing, 2011)

Seeing last week's transit of Venus was an exciting and humbling experience. More than just an interesting celestial phenomenon, it was an almost tangible link to astronomers of the past. Astronomers such as Jeremiah Horrocks, who was the first person to see a transit of Venus, in 1639; or poor Guillaume le Gentil, whose attempts to observe in 1761 and 1769 kept him away from home for more than nine years and only met with failure; Captain James Cook, who used the 1769 expedition to observe the transit in Tahiti as a base for exploration and discovery; or the Australian astronomers who used a Janssen apparatus to make a photoheliograph of the 1874 transit. 

I read about all of these people and the history of the transits of Venus and their effect on the world in a great book written by astronomer Nick Lomb. (Click on the book cover at left for more info.) The book is full of gorgeous colour: illustrations and diagrams from astronomers of past times; photographs of historic instruments; and modern astronomical images.

Astronomers such as Kepler, Halley and Isaac Newton—who all helped to predict and identify the dates of Venus transits—never saw the phenomenon themselves. Unfortunately, if you missed the one on June 6th this year, you probably won't get to see the next one, which is due in December 2117.

Inventiveness

Yesterday the planet Venus passed across the face of the Sun for the second time in a decade, although we won't see a similar sight for another century. I went to the University of Sydney where astronomy students and staff had put together a variety of telescopes and other equipment to observe this rare celestial event, despite viewing being limited to sporadic breaks in the clouds. I was particularly impressed with one piece of steampunk inventiveness: a large plastic funnel that had been converted into a viewing screen so that many people could see at once. Despite the clouds, we had an excellent view of the small black dot in its progress (you can see it at about the 7 o'clock mark in the image below). A big thank you to the University, staff and students who made it possible for ordinary observers like me to witness a twice-in-a-lifetime event!

Here's what Jules Verne said (in his book, Celebrated Travels and Travellers) about the 1769 transit, observed by Captain James Cook in Tahiti:

And now the moment for the execution of the primary object of the voyage approached. Cook accordingly took steps for putting the instructions he had received into effect....

On passing the sun, the rim of Venus was elongated as though attracted. A black point or dark ligament, a little less dark than the body of the star, was formed; the same phenomenon occurred upon the second interior contact.

"The observation," says Cook, "was made with equal success at the fort, and by those I had sent to the east of the island. From the rising to the setting of the sun, not a single cloud obscured the sky, and Mr. Green, Dr. Solander, and myself, observed the entire transit of Venus with the greatest ease.... We noted a luminous atmosphere or fog surrounding the planet, which rendered the actual moment of contact and especially of interior contacts somewhat indistinct. To this fact it is owing that our observations varied somewhat one from the other."

Jules Verne himself was alive for the transits of 1874 and 1882, although he may not have actually observed either event. I do hope you had an opportunity to see this one, and that some of us might still be alive in 105 years when the next transit occurs!