Planets like Venus, Mars, Jupiter and Saturn are easy to spot when they shine at their brightest but the outermost planet, Neptune, is a bit of a challenge even when at its best.
Now is the best viewing prospects of the year for Neptune as it reaches opposition on August 24th – meaning the gas giant is opposite the sun in our sky, and so will be visible all night long. Opposition also marks the planets closest approach to Earth – making it brighter than any other time.
Over the next few weeks Neptune will be some 4.3 billion km (2.7 billion miles) away from Earth – so distant that reflected sunlight off its icy cloud tops takes nearly 4 hours to reach us.
At this distance the planet’s 33,000 mile diameter is reduced to a mere 2.4 arc seconds wide (compared to much closer and bigger Jupiter’s 40 arc-seconds), but still shines at 7.8 magnitude – making it invisible to the naked eye but an easy target for binoculars.
The key in finding this denizen of the outer solar system is to know when and where to look.
It’s quite easy to find the general vicinity of Neptune – which lies amongst the starry background of the southern constellation Aquarius. The hardest part really is pinpointing which of those tiny points of light is the actual planet.
The planet rises above the eastern horizon after 8 pm local time and climbs to its highest point in the south around 1 am local time (Northern Hemisphere) before sinking below the west horizon before dawn.
For those with detailed star charts and GoTo scopes, its coordinate is RA 22h 15m 57.9m, Dec -11º 25′ 39″.
Here is how to hunt Neptune down in your backyard tonight: First look for two naked eye stars in the lower southern sky to point the way.
Neptune lies in the Aquarius constellation near the edge of its neighboring stellar pattern – Capricornus. Start your hunt with those two visible stars low in the southern sky in Capricornus – Nashira and Deneb Algiedi. Draw an imaginary line through them towards the upper left until hitting the next faintly visible star – Iota- Aquarii in Aquarius. Neptune is approximately 3 degrees to its upper left – equal to the width of your three fingers at an outstretched arms length.
I recommend first to try spotting Neptune using binoculars with the above starmap.
Best way to confirm your sighting is through a telescope. Center the object in the field of view and insert a high power eyepiece. If the object appears as a small blue-grey disk and not a point of light, then you’ve bagged Neptune!
Remember while you won’t see rich detail even through a large telescope, the real prize is in knowing you are actually watching live the most distant major planet in the solar system.
Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.