Chance to spot outermost planet

This week in Sky Watch, Ian Griffin focuses on the most faraway planet in our solar system, Neptune.

Ian Griffin
Ian Griffin

Over the past few weeks I have been enjoying some of the excellent films presented in Dunedin as part of the New Zealand International Film Festival.

A particular highlight for me was a showing of Emer Reynolds’ fascinating documentary The Farthest at the Regent Theatre. 

For over two hours I was totally enthralled by the surprisingly emotional story of the Voyager space missions to Jupiter, Saturn, Uranus, Neptune and deep interstellar space as regaled by members of the team that built these incredible robot spacecraft.

By happy coincidence, it turns out that Neptune, which features prominently in The Farthest, reaches opposition this week. With this in mind, and inspired by my own reaction to the film, this week I would like you to join me in a hunt for what is, thanks to Pluto’s demotion to ‘‘dwarf planet’’ status, now regarded by astronomers as the outermost planet.

Neptune
Photo: Getty images

Unfortunately, because it is so far away, Neptune is far too dim to see with the unaided eye. Despite being at opposition (the name given by astronomers to the time when an outer planet is opposite the sun in the sky as seen from Earth and therefore closest to us), the planet is still more than 4.3 billion kilometres away from us. In fact, Neptune is so far away that it takes its deep blue light more than four hours to reach us.

For the past few years, Neptune, which takes more than 164 years to orbit the sun, is moving through the constellation of Aquarius, the water-bearer, and if you do want to try to find it, then there’s an excellent opportunity next Wednesday evening, when the nearly full moon is just four degrees away from Neptune as it rises in the eastern sky.

As our chart shows, the best way to find Neptune is to locate the moon, and then, using a pair of binoculars, sweep upwards towards the star Hydor (which you should be able to see easily with your unaided eye). Neptune should be visible as a distinctly blue-coloured "star" between the moon and Hydor.

 

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