(Image from Wikipedia; full article here) At 83 km in diameter (~50 mi), Amalthea was the fifth discovered moon of Jupiter (the first four were the large Galilean satellites), and the last planetary satellite to be discovered by direct visual observation, as opposed to photographically. Given that the above Galileo images are among the highest quality available, it should be unsurprising not too much is known about this object. A couple of seemingly unrelated facts do constrain its history, though. First, Jupiter would loom in the sky, covering more than 45 degrees of arc; in other words, if you drew a horizon-to-horizon line, Jupiter would cover more than quarter of that. Second, recent observations strongly indicate that Amalthea is icy. Since the young planet was very hot, we can conclude Amalthea did not form where it is today. It either migrated from a more distant orbit, or was captured by Jupiter later in its history.
Monday, June 27, 2011
Moonday: Amalthea
(Image from Wikipedia; full article here) At 83 km in diameter (~50 mi), Amalthea was the fifth discovered moon of Jupiter (the first four were the large Galilean satellites), and the last planetary satellite to be discovered by direct visual observation, as opposed to photographically. Given that the above Galileo images are among the highest quality available, it should be unsurprising not too much is known about this object. A couple of seemingly unrelated facts do constrain its history, though. First, Jupiter would loom in the sky, covering more than 45 degrees of arc; in other words, if you drew a horizon-to-horizon line, Jupiter would cover more than quarter of that. Second, recent observations strongly indicate that Amalthea is icy. Since the young planet was very hot, we can conclude Amalthea did not form where it is today. It either migrated from a more distant orbit, or was captured by Jupiter later in its history.
Rain Today
The weather service has been predicting showers from this evening through Thursday, and here they come, right on schedule. It's nearly 80, with dewpoints (variable by station) in the mid 50's. To me, this feels slightly muggy, but not unpleasantly so. We've had so little warm weather in the first half of 2011 that this is quite appreciated. On the other hand, I adore warm weather rain, so I'm looking forward to the change, too. And, as there is a good chance this will be the last substantive precipitation we have until fall, I feel duty-bound to savor it. I'll get tired of unending clear skies, blistering sunshine and heat soon enough, just as I'm tired of clammy dampness right now.As general rule of thumb, I tell people that the PNW has the best weather in the world. We just have too damned much of it at stretch. This week may well end up being my favorite-weather-wise- of the year: plenty of variety.