Be the first on your block to see the planets Uranus and Neptune!
If you have a pair of binoculars, a detailed star chart showing where to look and a little experience, you can spot both Uranus and Neptune from your very own backyard (or wherever you view the sky). The sky also needs to be reasonably dark; no moonlight and as little light pollution as possible.
The seventh and eighth planets from the sun are both well positioned for viewing in the autumn evening sky this year.
These worlds were unknown for most of mankind’s time on Earth. The easiest planet to see is the Earth! Mercury, Venus, Mars, Jupiter and Saturn are all plainly seen without any optical aid. Mercury is the most challenging, never straying far from the sun’s glare. The others are quite bright and can be mistaken for bright stars at first glance.
Uranus was discovered accidentally by the great British astronomer Sir William Herschel in 1781 as he move this telescope across the stars. No one would have suspected another planet; he at first studied it as a comet. Continued observation showed that this as indeed the seventh planet from the sun.
Uranus is actually visible to the unaided eyes as a faint star, on a truly dark, rural night if you know just where to look. It shines at approximate magnitude +6, which is roughly the naked eye limit under average conditions. Binoculars are highly recommended.
Neptune is a lot fainter, nearly magnitude +8, but within reach of 10x50 binoculars if the night is dark and clear. It will appear just like any other dim star.
Once you spot it using a finder chart, look again a couple nights later, and Neptune’s movement in that time will be obvious.
A telescope, of say 6-inch aperture, will show Uranus as a small, pale green disc. Neptune appears bluish or gray; its disc is a lot smaller. Magnification of about 150x, however, should show it plainly.
Unlike Uranus, Neptune was not found by sheer accident. In 1846, two astronomers, John Couch Adams of England and Urbain Le Verrier of France, independently revealed Neptune in the telescope after searching for a suspected outer planet that was tugging on the orbit of Uranus by its gravitational pull. The difference between the expected position Uranus and its observed position was extremely sight, but enough to know something else was going on.
Similarly, the search was on for yet another outer world, by mathematical computation and the most careful scrutiny of the heavens. In 1930, Clyde Tombaugh found this “ninth planet,” Pluto, an extremely dim pinpoint of light among the thousands of other barely seen stars in the region. Since then, astronomers have found a host of other small worlds farther and smaller than little Pluto. These rocky outposts past Neptune have been reclassified as “dwarf planets.”
Only Pluto is visible to the “backyard” amateur astronomer, although a telescope of about 8- to 10-inch aperture is required.
If you get to see Uranus and Neptune, contemplate how truly far they are. Uranus averages 1.7 billion miles from the sun; Neptune, 2.7 billion. Pluto averages 3.6 billion miles away. Saturn, the farthest planet appearing bright to our eyes and known since men and women first gazed at the stars, is on average, 886 million miles away.
Guess which planet is closest! The Earth, of course. It is probably under six feet away from your eyes if you’re standing up.
Fathom their size. Uranus is about 31,000 miles wide; Neptune, 33,000 miles. The Earth is nearly 8,000 miles wide, and I have not yet traveled anywhere near around it. Uranus circles the sun once in 84.0 years. Neptune takes 164.8 years to orbit the Sun.
Water, methane and ammonia fluids surround Uranus’ rocky core. An atmosphere of hydrogen, helium and methane envelopes a thick mantle of ice that encases the rocky core.
This fall, Uranus is in the constellation Aries, to the east (left as seen from the Northern Hemisphere) of the faint line of stars marking Pisces. It is not close to any naked-eye stars to help in tracking it down.
Neptune is more conveniently placed. It is currently about one-half degree west (to the right) of the +4th magnitude star Phi Aquarii in the constellation Aquarius. A “half degree” is about the apparent width of the full moon.
Sky and Telescope Magazine (www.skyandtelescope.com) and Astronomy Magazine (www.astronomy.com) are two good sources to learn more about locating Uranus and Neptune.
Last quarter-moon is on Oct. 21.
Keep looking up!
Peter Becker is Managing Editor at The News Eagle in Hawley, PA. Notes are welcome at email@example.com. Please mention in what newspaper or web site you read this column.