409 Saturn’s Rotation

Saturn is the sixth planet from the Sun and is the second largest in the Solar System with an equatorial diameter of 119,300 kilometers (74,130 miles). Much of what is known about the planet is owed to the Voyager explorations in 1980-81. Saturn is visibly flattened at the poles, a result of the very fast […]

410 Meteoric Dust

Earth is a dirty place, and we aren’t getting much help from space. Every day, dust from meteorites, comets, and other 4.6 billion-year-old pieces of our Solar System fall into the Earth’s atmosphere. This meteoric dust is incredibly small, kind of like particles of smoke. But there is plenty of it. Until now, scientists […]

411 Uranus’ Orbital Plane

Uranus’ orbital plane tilts less than 0.8° from Earth’s orbit—the closest match in the Solar System. Uranus orbits the Sun once every 84 years. Its average distance from the Sun is roughly 20 AU (3 billion km). The difference between its minimum and maximum distance from the Sun is 1.8 AU, larger than that of […]

412 Days Are Getting Longer

Earth’s days are getting longer but you’re not likely to notice any time soon—it would take about 3.3 million years to gain just one minute, according to a study published in December 2016. Over the past 27 centuries, the average day has lengthened at a rate of about +1.8 milliseconds (ms) per century, a British […]

413 Origin of Comets

Where do comets come from? This question has nagged at astronomers and even terrified the masses for thousands of years. Danish astronomer Tycho Brahe brought the first semblance of order to comet science in 1577 when he showed that these objects lie far beyond Earth’s atmosphere. But real progress awaited studies in the mid-20th century. […]

414 Origin of Oxygen on Earth

Tanzanite (sorosilicate) Around 2.4 billion years ago, the Great Oxygenation Event (GOE) altered the air surrounding Earth from a primordial methane-rich atmosphere into the oxygen-rich one we breathe today. The driving force behind this change was cyanobacteria, single-celled life with the ability to photosynthesize. These microscopic creatures took in carbon dioxide and gave out oxygen. […]

415 Where is the Milky Way Headed

In 1783, English astronomer William Herschel looked at more than a dozen stars to see how they moved across the sky perpendicular to our line of sight. By analyzing these so-called proper motions, he determined that the Sun and its attendant planets are moving toward a point in the constellation Hercules called the “solar […]

416 Light from the Sun

The distance from Earth to the Sun varies because Earth’s orbit about the Sun is elliptical. At its closest, the distance is 91,402,000 miles, and its farthest distance is 94,512,000 miles. This gives an average distance of 92,957,000 miles. Light travels at 186,282 miles per second. Dividing the average distance by the speed of […]

417 Saturn’s Moons

What is a moon? In principle, it is a naturally occurring satellite of a planet. Many satellites in the solar system are like that. However, others are weirder-looking. The two moons of Mars, Phobos and Deimos, look more like small, irregularly shaped asteroids. It turns out that they probably are captured asteroids or debris from […]

418 Total Solar Eclipse

Only those located in the path of the Moon’s full shadow, its umbra, can see a total solar eclipse. The Moon’s umbra travels eastward at about 1,700 km/h (1,056 mph). A total solar eclipse can last for several hours. Totality at any location can range from a few seconds to 7 minutes 32 seconds, because […]