So the sky did crack open a few times last night between waves of fast-moving clouds. The stars were very bright in the hazeless air. Finding things in the sky mostly depends on good maps and a little persistence. Everything’s complicated by the spinning of the Earth, which like the classic mother-in-law stereotype, keeps moving the silverware. Over the coming week before the moon fattens up, we have a ideal opportunity to find planet number eight in a pair of binoculars.
Neptune (at right) was discovered on September 23, 1846 by Johann Galle at the Berlin Observatory based on a mathematical prediction by French mathematician Urbain LeVerrier. Astronomers had observed irregularities in Uranus’ orbit and based upon those, predicted the existence of an outer planet. Amazingly, Galle found the planet within one degree of the prediction. British mathematician John Adams independently came up with a similar solution, so the the discovery is shared jointly by the two men.
Looking south around 10-11 p.m. in early September. Step one in your quest to find Neptune is to use brillliant Jupiter and the star Altair, located at the bottom of the Summer Triangle, to form a triangle with the stars Alpha and Beta in Capricornus. Two fists to the left or east of Alpha-Beta, you’ll find Delta. If you get this far, use the detailed map below to zero in on Neptune. — created with Stellarium
At 2.7 billion miles from Earth and about four times our size, Neptune is a mid-sized planet like Uranus. Beneath its hydrogen, helium and methane atmosphere, it’s composed of a mix of ices and rocks. For more on Neptune you can re-visit this blog.
Finding Neptune requires at least moderately dark skies and a pair of 7×50 or 10×50 binoculars. The key is the aperture or size of the lenses of your binoculars. The number ’50’ in 10×50 stands for the lens size in millimeters. 50 millimeters equals about two inches. You’re going to need that size lens or larger to spot the planet. The ’10’ in 10×50 is the magnification. Anywhere from seven on up is good. 10 power is ideal.
A binocular view of the sky near Delta. Point your binoculars at Delta and move them upward just a bit to find what I call the "index finger". To the right of the finger, you’ll find a triangle of dim stars. Look for three stars in a row there. Neptune is the "star" in the middle of the row. — created with Chris Marriott’s SkyMap Pro at www.skymap.com
OK, let’s give it a try. We always start with the brightest thing you can see. That’s Jupiter and it’s blazing in the south. Use the first chart to get you to Delta in Capricornus. The second, closeup chart (above) will point you to Neptune. Remember to allow your eyes time to get used to the dark before you attempt this challenge. 10-15 minutes is good. It’s also important to focus sharply on the stars and brace the binoculars against a wall or car to keep them steady.
Over the next few nights, Nepture will move ever so slowly westward (to the right), breaking the neat line it makes tonight. It’ll stay in the neighborhood for some time however since the planet takes 165 years to go just once around the sun.
If you have success, I congratulate you! What the heck, you deserve a pat on the back just for trying. And of course we’d love to hear of your experience whether you found the planet or not. Just add your comment by clicking on the link below.