If you happen to catch this eclipse and are waiting for a total one, you won’t have to wait too long. Make plans for August 21, 2017. On that day a total eclipse will cross the US from Oregon to South Carolina, making it within a day’s drive of most of the country.
Impact Factor
The moon is known for its cratered surface. Its lack of atmosphere and proximity to Earth make it easy to observe impact craters from past collisions. Since the Earth and Moon are in the same general region of the solar system, they were likely bombarded at similar rates. While we do find craters on Earth (such as Barringer crater in Arizona), they are typically not as obvious due to wind and water erosion.
Water from the Sun
The Moon is a dry, airless rock. At least that is how we imagine it. At basic level, that’s a pretty accurate description. It is drier than any desert on Earth, and its surface would be considered a hard vacuum. But at a more subtle level, that isn’t quite true. The Moon does have the faintest trace of atmosphere, consisting of elements such as argon, helium and hydrogen. The Moon also has traces of water on its surface, mostly locked up within minerals.
Somewhere Across the Sea
When we look at the Moon, we see a surface pocked with craters, scattered between seas of basalt from ancient lava flows. Since the Moon is not geologically active, it’s easy to imagine that the formation of lunar seas was triggered by large impacts. That’s actually been the dominant theory for some time. Now new research indicates that for at least one of the great seas, Oceanus Procellarum, that isn’t the case.
The Reveal
An occultation is where one object passes in front of another from your vantage point. It is similar to an eclipse or transit, but in this case the occulting object completely blocks the more distant object. Typically occultations occur when the moon occults planets, or when solar system objects occult stars.
Metonic Moon
Today the Moon is in its New Moon phase. This won’t happen again for another 19 years. Actually that isn’t quite true. It takes about 29.5 days for the Moon to go from one new moon phase to the next, so we’ll have a new moon roughly once a month, just like always, but there is a periodicity to moon phases that spans 19 years, and it is known as the Metonic cycle.
Titan Fall
Titan is the largest moon of Saturn, and the second largest moon in our solar system. It has a greater diameter than Mercury. It is also the only moon with a thick atmosphere. It has liquid methane rivers and lakes, and has a seasonal climate.
And like our moon, we have landed a probe on its surface. In 2005 the Huygens probe made a one-way journey to the surface of Titan. You can see a video of that landing above.
Wave the Titanic
Saturn’s largest moon Titan is in some ways very similar to Earth. Sure, it is significantly colder, and has a much thicker atmosphere, but it has something no other world besides Earth. Lakes and seas. These are not water lakes, but methane. With a surface temperature of about 94 K, and a thick atmosphere, Titan is perfect for a methane …
Splat
The mass of the Moon is about 1% that of Earth. That might seem pretty small, but it’s actually surprisingly large. The moons of other planets are tiny when compared to their planet’s mass. Just how Earth got such a large moon has been a bit of a mystery, but it has generally come down to two models: co-formation and collision.