Challenge #2 – Spotting The Planet Uranus

Uranus Statistics

TargetTypeRight AscensionDeclinationConstellationMagnitudeSize
UranusPlanet02h 02m 30s+11° 56′ 09″Aries+5.83.6 arcseconds

Data is precise for 15th January 2020

Where to find Uranus

At less than four arcseconds across, finding the little green dot of Uranus is a good challenge for a small telescope.

In January the planet transits (reaches its highest point in the sky above the southern horizon) an hour after sunset and, with no moon in the sky, this is a great time to try and find it.

The screen grab below from SkySafari 6 shows you the view of the sky at 7pm from the central US. See Uranus about two thirds of the way between the horizon and the overhead point (Zenith) in the consolation of Aries. Click the image for a full screen version.

William Herschel discovered the planet in March 1781 with his home-made 6 inch telescope. He observed it on several more nights after that first spotting, and noted its movement against the background of stars. He also noted that the light source was a disc and not a point of light, as he initially believed he’d discovered a comet. It was only later, after more observations and math, that it became clear he had found the solar system’s newest planet.

Herschel certainly wasn’t the first person to see Uranus because it has naked eye visibility in a dark sky, and there were plenty of those in the 1780s. Records show that Uranus had been observed at least 20 times prior to Herschel giving it particular attention, but no one believed it was anything more than a green-hued star.

The planet orbits the sun at such a distance that it takes 84 years for it to complete one full circuit. This means that one Uranian year is the measure of a good human lifetime!

Once you’ve located the right area of the sky to begin your hunt, it is time to zoom and concentrate our efforts on locating the planet itself.

The next screenshot shows Uranus sat between Aries, Pisces, and Cetus. Stars are shown down to magnitude 7 which you should expect to see through a magnifying viewfinder.

Let’s zoom in one last time to see what the planet looks like an 1 degree field of view, as shown by the blue circle. The stars in this image are shown to magnitude +10.0, which should give a good approximation of the view through your eyepiece. Click on the picture for a full screen version.

You won’t do any better than seeing the planet as a small greenish disc, but you will have seen what great astronomers before you discovered 250 years ago, the second most distant planet from the sun, slowly wandering around our solar system.