Patrick Van Etten, Jr., age 13, of Freeport, I11., for his question:
HOW WAS THE PLANET NEPTUNE DISCOVERED?
For a time Uranus was thought to be the most distant planet from the sun. Neptune is about 30 times as far from the sun as is the earth, and Pluto is even farther. Neither of these planets can be seen without a telescope. Before astronomers had ever seen Neptune or Pluto, they had "discovered" them by using mathematics.
Early astronomers had noticed that Uranus was not always in the position they predicted for it. The force of gravity of some unknown planet seemed to be influencing Uranus.
A young English astronomer and mathematician named John Adams began working to find the location of the unknown planet in 1843. Adams predicted the planet would be about 1 billion miles farther from the sun than Uranus. It was the planet Neptune.
Adams completed his remarkably accurate work in September of 1845. He sent it to Sir George Airy, the Astronomer Royal of England. But Airy, apparently lacking confidence in Adams, did not look for the planet with his telescope.
Meanwhile, a young French mathematician named Urbain Leverrier began working on the same project, unknow to Adams. By the summer of 1846, Leverrier also had predicted the position of Neptune.
Leverrier sent his predictions, which were similar to those of Adams, to the Urania Observatory in Berlin, Germany. Johann Galle, the director of the observatory, had just completed a chart of the fixed stars in the area of the sky where the unknown planet was believed to be.
On September 23, 1946, Galle and his assistant, Heinrich d'Arrest, searched with a telescope for an object that was not on the chart. They found Neptune near the position predicted by Leverrier.
Today, both Adams and Leverrier are credited with the discovery. The planet was named Neptune for the Roman sea god.
Neptune's diameter is almostd four times the earth's diameter. The planet travels around the sun in an elliptical or oval shaped orbit. It goes around the sun once about every 165 earth years, compared to once a year for the earth.
Neptune is so far from the earth that astronomers do not know much about its surface. They believe the portion of Neptune visible from the earth is the top of a thick layer of clouds. These clouds may consist of frozen ammonia, or combinations of ice crystals, frozen methane and frozen ammonia.
The atmosphere surrounding Neptune consists chiefly of hydrogen and methane gas, with some helium and ammonia. Astronomers believe this atmosphere is about 2,000 miles thick.
The tilt of Neptune's axis causes the sun to heat the planet's northern and southern halves unequally, resulting in seasons and temperature changes.
Astronomers do not know whether Neptune has any form of life.
Two satellites or moons travel around Neptune. One is named Triton and the other is called Nereid.
For latest information on Neptune go to Science News in YouAskAndy main menu and click on NASA Jet Propulsion Laboratory