Observing Project 11A Uranus and Neptune at the Eyepiece

At first glance it would seem that the triumph is in simply finding the two icy giants at the edge of the solar system. But with sufficiently large instruments and a little patience and skill, you can coax some of the secrets of the ice giants out of those pale blue-green dots.

Uranus shines at a feeble magnitude +5.7 and through a telescope its disk spans not quite four arc seconds. Even if Uranus had some details to see, you could not see them through amateur telescopes anyway. What may surprise some is that the planet's moons are visible through large amateur telescopes. The two outer moons, Oberon and Titania, are both magnitude +14 when the planet is at opposition. This puts them at the extreme visual range of a 10-inch telescope, which with the advent of the Dobsonian many astronomers can now afford that aperture. Ariel is slightly fainter at magnitude +14.2. Umbriel is magnitude +15.1 and requires at least 14

inches and Miranda is the faintest at magnitude +16. It takes some work, patience and well cared for equipment but if you are willing to do the work, you can coax out all five of Uranus' moons if you have sufficient aperture available.

Many of the same tricks that you used at Mars to coax out Deimos and Phobos will work here too, although the glare of Uranus is not much of a factor here. What matters here is unlike at Phobos and Deimos, you are working at the most extreme limits of your equipment. Therefore it is absolutely essential that you avoid any extraneous light at all. If you have a dew cap, put it over the telescope and do whatever it takes to avoid any exposure to non-essential light.

In 1978, astronomers took advantage of a fortuitous event when Uranus passed directly in front of a star. As the planet neared the star, it faded and recovered to normal brightness nine times. After being occulted by the planet, the cycle reversed itself after the star reappeared. Check your ephemeris for occultations of stars by Uranus. This will present you with an opportunity to recreate one of the most important discoveries in the history of astronomy. The finding that Uranus had rings showed that Saturn's ring system was not unique in the universe, rather ring systems were commonplace around large planets. You can do this in a telescope of any size. Between 2005 and 2015, Uranus' rings will be involved in seven occupations, including three events alone in 2006. All three of the 2006 events involve stars brighter than magnitude +10.

About a billion and a half kilometers further out Neptune stands watch over the outermost fringe of the domain of the planets. Neptune's gravity shepherds the objects of the Kuiper Belt beyond its orbit maintaining many of the ice chunks beyond its orbit in a 3:2 resonance. Neptune's light is even more feeble than that of Uranus, shining at only magnitude +7.8 and subtending barely 2.3 arc seconds. Neptune's one large moon, Triton, shines brighter than any of Uranus'. At magnitude +13.4, Triton is at the extreme range of an 8-inch telescope. Again, make sure the telescope objective is shaded and avoid any light whatsoever.

Remember that Neptune also has rings, so if any prediction of an occultation of a star by Neptune appears, make sure you watch. As Neptune approaches the star, what will happen as the rings pass by? Neptune will occult eight stars between 2005 and 2015, including two events in 2006.

The subtle details of Uranus and Neptune can challenge you and your equipment to their limits. Watch the excess light, shade that scope and find a dark sky site. If you keep your scope well collimated, you might surprise yourself as to what you can really see. But there are some objects in the heavens that are just too faint for the eye to see. Yet that does not necessarily mean that you can't image these sights.

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