Marco Polo
Trips to the beach or the mountains are exciting, but how about a trip around the world to...
In the 1700s the astronomer Edmond Halley studied historical records of the appearance of comets. Noticing some patterns, he theorized that three recorded comet sightings over the preceding 300 years were all actually of the same comet on different solar orbits. Using this information, Halley almost precisly predicted when the comet would return. Ever since, we've called this comet "Halley's Comet." It is visible on Earth every 75 or 76 years. The author Mark Twain was born when the comet was highest in the sky in 1835 and died when it was highest in the sky in 1910. Most recently, Halley's comet passed Earth in 1986, but light pollution from urban areas made it almost impossible for people in the United States to see. Fortunately, several spacecrafts photographed it, and many probes flew through its tail, collecting data about its makeup. Halley's Comet won't pass Earth again until 2061.
Trips to the beach or the mountains are exciting, but how about a trip around the world to...
Cities have been around for thousands of years; the first ones appeared in about 3,000 BC....
Ancient Greece was one of the most highly advanced civilizations in history. It flourished...