Marc Schare, age 11, of Staten Island, New York, for his question:

Has the planet Vulcan been seen since 1859?

In the 1800s, certain astronomers were sure that another planet existed in our solar system between Mercury and the sun. This possibility was suggested by the French astronomer Leverrier. On March 26, 1859, an amateur astronomer named Lescarbault observed a dark dot passing across the sun. From this data Leverrier calculated its orbit and named it the planet Vulcan. He hoped to verify his theory during an eclipse in 1860    but Vulcan did not appear.

Astronomers began to doubt its existence. But two more flurries of excitement occurred. On April 4, 1875, Heinrich Weber of Germany was viewing an eclipse in China. He too saw a dark dot, but the observatories of Greenwich and Madrid assured everybody that it was merely a sunspot. During an eclipse on July 29, 1878, an observer in Wyoming and another on Pikes Peak saw what they thought was Vulcan. The object proved to be a star. Since that time no more Vulcan sightings have been reported and modern astronomers are almost sure that no such planet exists.