Hunting for Neptune

What are you doing next Tuesday?

If you are at a loose end, there’s an excellent chance to enjoy a beautiful close approach between the waxing moon and the planet Venus.

The action occurs after sunset in the constellation Aquarius. You will need to find an observing site with an unobscured view to the west.

There’s a relatively narrow window to see this event; before 10pm, the sky will be too bright, and after 10.30pm, the moon and Venus will be getting close to the horizon. Remember to pack a camera!

The moon’s age will be just over three days past new. Our closest celestial neighbour will appear as a slender crescent, with only eleven percent of its visible surface directly illuminated by the sun.

As the sky darkens, you will see the remaining part of the moon’s surface illuminated by earthshine, which is sunlight that reaches your eyes by reflecting off both the Earth and the moon.

Venus will be easily visible below and to the right of the moon, shining like a very bright ‘‘star’’. On Tuesday It will be just over 166 million km from us. The light you see when looking at the planet, travelling at 300,000km every second, has taken roughly nine minutes to reach your eyes.

If you have binoculars or a telescope, point them at this celestial spectacle, since there’s one more planetary surprise lurking nearby, which needs optical aid to be seen. The planet Neptune is less than a degree from Venus in the sky.

If you haven’t yet ticked off the outermost planet from your planet-spotting bucket list, this is a perfect chance to do so.

To find Neptune, point your telescope or binoculars at Venus. Slightly to the left and below the planet will be an orange-red star. This is Phi Aquarii, a giant star that is 202 light years from the sun. Now extend an imaginary line from Venus through Phi Aquarii and look for a pale-blue dot. Congratulations, you have found the planet Neptune, presently 4.5 billion km away.

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