The natural Navigation: The Right Course, Naturally

What a difference an hour makes, I took this photo only one hour later than yesterday’s. Venus was still visible to the naked eye, but being drowned out by the minute as the morning’s twilight becomes dawn itself. Twilight is a hugely important time for celestial navigators as it is the only time that both the stars and horizon are visible. Celestial navigation relies on using a sextant to measure the angle between stars and the horizon. Before the morning twilight the horizon is not visible and after it the stars have disappeared. In the evening it is of course the other way round.

I woke up in the middle of the night and couldn’t go back to sleep. Some compensation was to be found outside, with a beautiful view of Orion, Sirius and Venus. All three have historically had some significance. Both Orion and Sirius have been used as seasonal markers, the ‘heliacal rising’ of Sirius being used as a forecast for flooding of the Nile in ancient Egypt. Orion is still known as a winter constellation in the northern hemisphere. The references to Venus are legion and include its use by the Maya to time the start of wars (see Anthony Aveni’s excellent book, ‘People and the Sky‘, for more on that.)

The picture is of Venus rising in the east-northeast just before five this morning, it took many attempts to get this photo as a cold wind kept rattling the tripod and its owner.

One of the many aspects…

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This photo, taken just before six this morning, sums up my senses’ delight at being woken by our kids who decided to hold a animated conference about dinosaurs at half past five. A slightly blurred Venus can just be seen between equally blurred leaves and clouds. If you do happen to be up even earlier, and the clouds allow, then Venus is currently an impressive pre-dawn beacon in the east.

I was up early this morning and caught a great twilight show from Jupiter and Venus. This photo does not do Venus justice, but you might just be able to make it out in the centre of the picture between the two banks of cloud.

Jupiter’s orbit is outside earth’s and so moves through the night sky quite slowly, about one constellation per year.

Venus’ orbit is closer to the sun than ours and so its position in the sky changes quite rapidly. It spends about seven months as a bright object in the early evening sky, before disappearing behind the sun’s glare for about four months and then re-emerging in the early morning for seven months. It then repeats the cycle. Ancient civilisations were divided in their understanding of it, some realising that it is a planet and others giving it two labels, ‘morning star’ and ‘evening star’, without…

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