Autumnal Equinox and Observing the Outer Solar System

Thank goodness summer is almost over. Autumn, or fall, begins on September 22 at 10:49 am EDT. For most of the country, 2012 has been a very hot and dry year. And for us in southern New England, we’ve had more than our fair share of heat, humidity, and severe thunderstorms. I for one will be happy to welcome in the cooler days of fall that usually bring less hazy skies for all local stargazers.

What do the starry heavens have in store for us during the next several months? How about the planets of the outer solar system? Beginning on September 1, I encourage anyone with an interest in astronomy to visit one of the local observatories to catch a glimpse of Uranus, Neptune and yes, Pluto. While Pluto was demoted to dwarf-planet status back in 2006, I still like to consider it to be a more prominent solar system member.

Unless you know specifically where to look, these distant bodies can be difficult to locate. Uranus can be seen in a dark sky with the naked-eye, but Neptune requires at least binoculars to find it. Both planets reveal a blue-green disk with medium to high magnification. A fairly large computer-controlled telescope is required to locate Pluto. This dwarf-planet will look like one of the many faint stars occupying the same field of view. Assuming the computer correctly positioned the telescope, Pluto will be one of those points of light you can see through the eyepiece.

Here’s how the rest of 2012 plays out for observing our distant planetary (regular or dwarf) neighbors:

On September 1 at 9:00 pm, Pluto will be about 28 degrees above the southern horizon in the constellation of Sagittarius, a little west (to the right) of the north/south meridian. It can be found above the “teapot” asterism amongst the stars of the Milky Way, and less than one degree from the open star cluster M25. Pluto is very dim, at about 14th magnitude. Not surprising since it is then 2.9 billion miles from the Earth. Locally one can see stars down to a magnitude of 5.5 to 6 with the naked-eye in a dark sky. Without a computer-controlled telescope Pluto can be quite a challenge to locate visually by reading star maps and star hopping across the sky to find it. Many of the local observatories’ telescopes are computer-guided, so don’t hesitate to ask the volunteer operator to dial up Pluto.

Pluto now has five known moons, the latest discovered by the Hubble Space Telescope on July 11 of this year. None of these moons can be seen in any amateur telescope. A spacecraft named New Horizons is currently en route to Pluto to conduct a mapping mission during its fly-by of this distant “former” planet. It was launched on January 19, 2006, and will arrive at Pluto on July 14, 2015. That’s a nine and a half year journey. And you thought that summer vacation drive with your family was long!

On the same night and time Neptune, about 2.7 billion miles from the Earth, can be found about 20 degrees above the southeast horizon in the constellation of Aquarius, shining at a magnitude of 7.8. When viewed through a telescope an observer can see the bluish-green disk of the planet. You won’t be able to see any details in the cloud tops of this cloud-enshrouded world, but how many people can say they actually observed Neptune? This world has 13 known moons. The largest one, Triton, can be viewed with a 10-inch telescope.

Also on that evening at 9:00 pm, Uranus, shining at magnitude 5.7, can be located only seven degrees above the eastern horizon in the northern part of Cetus on the Pisces border. Many of the local observatories are not located in an area that affords them a view of objects this close to the horizon. You’ll have to wait until later in the evening, or wait until mid to late September for Uranus to move higher into the sky. Uranus will show a much larger bluish-green planetary disk than Neptune, but this cloud enshrouded world will also not reveal any details in its cloud tops. Uranus will be about 1.8 billion miles from the Earth. It has 27 known moons. The five major ones are Titania, Oberon, Ariel, Umbriel and Miranda. The first two require a 14-inch telescope to observe, while the second two only need a ten-inch scope. Miranda requires something a little larger.

By mid-month our distant planetary neighbors will be farther west of their early month positions. Uranus will be much easier to observe as it rises above the tree-line and out of the horizon haze to the east. On September 16 Uranus will move into the constellation of Pisces, and it will be at its closet distance to the Earth on September 29.

As year progresses, the planets will be moving west each successive evening. On October 1 Pluto will be in the southwest, around 20 degrees above the horizon. Neptune will be about 34 degrees above the south-southeast horizon. And finally Uranus will be high in the east-southeast about 29 degrees above the horizon.

Beyond October we will be able to continue to observe Pluto until mid to late November. Neptune will be observable through December at least, while Uranus will be visible to about mid-February 2013. Of course, these visibility forecasts are all dependent upon the area of the sky not being blocked by trees and buildings at the local observatories.

Finder charts for Uranus and Neptune can be found on the Skyscrapers website at:

In conclusion, if you don’t own a telescope capable of showing Uranus, Neptune or Pluto, or you can’t seem to find them on your own, then visit one of the facilities below. The volunteer telescope operators will be more than happy to provide a glimpse of these planetary bodies that reside in the outer depths of our solar system.

Seagrave Memorial Observatory in North Scituate is open for public viewing every clear Saturday night. Our current hours are from 8:00 – 10:00 pm, weather permitting.

The darkest skies in Rhode Island are available to stargazers every clear Friday night at Frosty Drew Observatory in Charlestown. Please check the website for open times.

Ladd Observatory in Providence plans on reopening in mid-September. Check the website for any updates.

Good luck and keep your eyes to the skies.

David A. Huestis

David Huestis
David Huestis
Entry Date:
Sep 12, 2012
Published Under:
David Huestis's Columns
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