Facts about Pluto

• Pluto was demoted to a Dwarf Planet in 2006.
• It is one of the largest objects beyond Neptune.

Diameter: 1,433 miles
Mass: 0.0025 Earth’s mass
Density: 2.03 where water = 1
Gravity: 0.08 times that of Earth
Albedo (% of Sunlight reflected): 30%
Rotation on Axis: 6.4 days
Inclination of Axis to Orbit: 123°

Distance from Sun: 3,674,490,000 miles
Revolution about Sun: 248.03 years
Inclination of Orbit to Earth’s Orbit: 17.15°

Atmosphere: Methane gas? Some nitrogen?
Surface Temperature: –419° F

Moons: Pluto has 4 moons.

Most interesting features in a small telescope: Pluto cannot be observed in any small telescope, however, it is possible to photographic it with a small telescope, but this is beyond the scope of beginners. Click here for an article on imaging Pluto with a small telescope.

Right. An image of Pluto created by taking many pictures of this outer Dwarf Planet by the Hubble Space Telescope.

THE DWARF PLANET PLUTO

CLICK HERE for a thorough explanation of why Pluto was demoted from a planet to a Dwarf Planet. However, the short story is that with better telescopes and imaging techniques, astronomers discovered that immediately beyond Neptune, there is a debris field of leftover material from when the solar system formed and that Pluto is just one of the larger pieces in this debris field. When the first asteriod, Ceres, was discovered in 1801, it was also called a planet until more and more asteriods were discovered—then astronomers demoted Ceres to “just” an asteroid.

Little is known about Pluto because of its distance and small size. It is smaller than many of the moons in our Solar System. Until the New Horizons spacecraft flys by Pluto in 2015, it will keep its secrets. At this time, astronomers guess that the surface of Pluto will be comprosed of ices and rocks, accounting for the bright and darker surface coloration as seen in the above picture, generated from many pictures taken by the Hubble Space Telescope.

Pluto’s orbit is highly inclined to the other Planets. Also, its orbit is not concentric with the other Planets. Instead, for about 20 of the 248 years that it takes to circle the Sun, Pluto’s orbit is closer in than Neptune’s. The last period when Pluto was closer to the Sun than Neptune was from 1979 to 1999.

Observing Pluto
Pluto is difficult to locate because it is so faint, about magnitude 14, and requires AT LEAST a 12-inch telescope. Pluto does not appear as a disk and its moon, Charon cannot be seen. A large telescope, detailed star charts and three to four days of comparative viewing are required to ferret Pluto out from a background of faint stars. Needless to say, Pluto is an object for the better equipped and more experienced observer. During the years 2000 to 2050, Pluto slowly moves east from the constellation Ophiuchus to Aquarius.

The Story of Pluto’s Discovery

Clyde Tombaugh the discoverer of Pluto, was born in 1906 and raised on farms in Streator, Illinois and later, Burdett, Kansas. His interest in astronomy came early but was piqued at age 12 when he observed through his uncle’s telescope. After high school, Clyde stayed to help on the Kansas farm. In 1928, he made drawings of Jupiter’s cloud belts and Mars’ surface colorations with a 9-inch diameter telescope mirror that he had ground and polished. Always inquisitive, he sent these drawings off, with questions, to the Lowell Observatory in Flagstaff, Arizona. They were so impressed with the drawings and his interest in astronomy that they offered him a job! So, on January 15, 1929, at the age of 22, Clyde Tombaugh arrived by train in Flagstaff as an astronomer’s assistant.

At the time, Lowell Observatory was gearing up to search for a ninth planet, code named “Planet X” by its founder, Percival Lowell. A new and special 13-inch photographic refractor had been ordered and arrived a month after Tombaugh.

In April, Clyde started the arduous and systematic search for the planet, photo-graphing the night sky around the ecliptic, the path in the sky subscribed by the Sun over the course of a year but also the path where the other Planets roamed.

He took two photographs of the same area of the sky on glass plates a week apart, then compared them in a special-type microscope called a blink comparator. This instrument allowed viewing a superimposed image of the two plates while it alternated the view between them about three times a second. Any “star” that moved from one plate to the other would appear blinking in the “combined” image.Over the course of the year, the Planet X project became Tombaugh’s sole responsibility.

On February 18, 1930, Clyde resumed blink-ing plates having a very high density of stars, taken from a section of the Milky Way in the constellation Gemini, near the star Delta Geminorum. The going was slow, but in the early afternoon, Clyde noticed a star blinking on and off, an indication that it had moved. He checked and double checked before calling it to the attentions of the staff astronomers. However, he did not need their verification to know that he had found Lowell’s Planet X.

Planet X was named Pluto after soliciting suggestions from the public. The winning entry came from an 11-year-old girl from England. Pluto, the Greek god of the Underworld was an appropriate name for a Planet in the outer reaches of the Solar System.

In June/July 2011, a 4th moon of Pluto was discovered. It is designated P4 in this picture. Could there be a 5th or more?

The New Horizons spacecraft that will fly by Pluto in 2015. It will not orbit Pluto, just fly by it and take pictures!

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