Earth at Aphelion

On the 4th of July, you will be farther from the sun than at any other time of the year. Earth's orbit around the sun is not a perfect circle, it's an ellipse, and on July 4th, Earth is at the end of the ellipse farthest from the sun. Astronomers call this "aphelion." When we are at aphelion, the sun appears slightly smaller in the sky (by about 1.7%) and global solar heating is actually a little less (by about 3.5%) than the yearly average.

New Discoveries at Mercury

Mercury's magnetic field is "alive."

The soaring Teotihuacan Stone Pyramids

Archeologists are opening a cave sealed for more than 30 years deep beneath a Mexican pyramid to look for clues about the mysterious collapse of one of ancient civilization's largest cities.

The soaring Teotihuacan stone pyramids, now a major tourist site about an hour outside Mexico City, were discovered by the ancient Aztecs around 1500 AD, not long before the arrival of Spanish explorers to Mexico.

But little is known about the civilization that built the immense city, with its ceremonial architecture and geometric temples, and then torched and abandoned it around 700 AD.

( Cave System )