Pluto Demoted Day

Pluto was a planet for 76 years, but now it's not. It got demoted. Pluto Demoted Day commemorates the date in 2006 when the International Astronomical Union (IAU) demoted Pluto from planetary status and designated it as a dwarf planet. At the time, new rules said in order for a celestial body to be a planet it must orbit around the Sun, have a nearly round shape, and "clear the neighborhood around its orbit." Pluto doesn't meet the third criteria because its orbit overlaps that of Neptune for about 20 years of its 248-year orbit. For that period of time, it is closer to the Sun than Neptune is. Being that Neptune is much larger, it still is considered to be a planet.

But just because Pluto got demoted, it doesn't mean that it has become neglected. On the contrary, NASA's New Horizons spacecraft flew through Pluto's system in 2015, taking the first close-up images of Pluto and its moons. With a continued focus on this one-time planet, it is only right that we celebrate it, even if it doesn't have the stature it once did.

Percival Lowell was the first to propose that the planetary body that turned out to be Pluto existed. Wobbles in the orbits of Uranus and Neptune had been detected, and he thought they must be caused by the gravitational pull of an unknown planetary body. Lowell determined the approximate location of the body and tried to locate it for more than a decade, to no avail. In 1929, at the Lowell Observatory in Arizona (named for Percival Lowell), the search for the planet started again, with calculations previously made by Percival Lowell and W.H. Pickering being used as a guide.

On February 18, 1930, Clyde Tombaugh found Pluto while using a blink microscope combined with photographic plates at the Lowell Observatory. The discovery was publicly announced on March 13, on the anniversary of Lowell's birth and of the discovery of Uranus. At the time, Pluto was deemed to be a planet, although it is now considered to be a dwarf planet. It was named after the Roman god of the underworld, and its name was given to it by Venetia Burney, an 11-year old girl from Oxford, England. She suggested the name to her grandfather, and it was selected after he forwarded it to the Lowell Observatory.

Pluto is in a region called the Kuiper Belt, where other icy bodies and dwarf planets are located. It is 4.5 billion miles away from Earth, and averages a distance of 3.6 billion miles from the Sun, being almost 40 times farther away from the Sun than Earth is. It takes Pluto about 248 years to complete its oval orbit around the Sun, and a day on Pluto is 153 hours long. Pluto is 1428 miles in diameter, making it about two-thirds the size of the Earth's moon and about half the width of the United States.

Pluto has a thin atmosphere consisting mainly of nitrogen, along with some methane and carbon monoxide. Its surface temperature is between -350 and -400 degrees Fahrenheit—so cold that life likely can't exist there. Because of its distance from the sun, it is also very dim on Pluto, with daylight being comparable to the time just after sunset on Earth. The landscape is made up of mountains, valleys, craters, and plains. A heart-shaped glacier that is about the size of Texas and Oklahoma combined is perhaps its most distinct feature. Pluto has five moons, with Charon being its largest, which it rotates with. Discovered in 1978, Charon isn't much smaller than Pluto, being 737 miles in diameter. Pluto may have gotten demoted, but as is apparent, there is plenty to celebrate about it on Pluto Demoted Day!

How to Observe Pluto Demoted Day

Some ideas on how you could spend the day include:

• View photos of Pluto from NASA.
• Learn more about the New Horizons spacecraft and its Pluto mission.
• Find out your "Pluto time."
• Visit the Lowell Observatory or another observatory.
• Learn more about Clyde Tombaugh and Percival Lowell.
• View the sky with your own telescope.

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