A gathering of the planets

LOOKING WEST AT 8.30PM ON THURSDAY, OCT 11
LOOKING WEST AT 8.30PM ON THURSDAY, OCT 11

One of the wonderful things about the new planetarium at Otago Museum is that it allows the very talented team of science visualisers to scan forwards through time and study the relative motions of the planets over weeks and months, Ian Griffin writes.

Ian Griffin
Ian Griffin

Using sophisticated virtual-reality software, it's possible to identify particularly spectacular events in the sky in advance, in order to promote them to all and sundry. 

It was using this approach that the team identified something rather special taking place in the sky over the next couple of nights.

If the sky is clear, then it's well worth rounding up the whanau and heading to a location with an unobstructed view of the western horizon.

While the event is easily visible to the unaided eye, to get the most out of the experience you will need a pair of binoculars or, better still, a small telescope.

So what's happening that's worthy of such special attention?

In short, it's a gathering of the planets.

For the next couple of nights, as the sky darkens after sunset, it will be possible to see Mercury, Venus, Jupiter and a stunning waxing-crescent moon close together in the western sky.

Mercury will be hardest to spot, as it is relatively dim and quite close to the horizon. As our chart shows, tomorrow night the innermost planet will be almost directly below Venus.

If you have a pair of binoculars point them at Venus (taking a few moments to admire its gorgeous crescent shape) and then slowly scan down towards the indicated position of Mercury.

Tomorrow night the moon will be just two days past new, which means only 5% of its surface is illuminated by sunlight. It will form a lovely right-angled triangle with brilliant blue-white Venus and yellow-white Jupiter.

As the sky darkens, depending on atmospheric transparency, you might be able to see the other 95% of the lunar surface dimly illuminated by ghostly earthshine.

On Friday night, the moon, which will be approximately 11% illuminated, will be higher in the sky, to the right of Jupiter.

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