What We Still Don't Know...

Boy, if this post really tried to sum all of that up, it would be a really long post! I guess a better title for it would be "a specific question that we still cannot answer:"

Why does the moon look so big when it is close to the horizon and so small when it is higher in the sky?

(told you I'd write about this soon)

You may think you know the answer. We've all heard the most popular one- the "horizon perspective" explanation- which claims that it only "appears" bigger because you are seeing it next to houses and trees and whatnot, but as this NASA article shows, that does not fully explain it. In fact, no one really knows for sure! Is it because of the apparent "dome" shape of the sky? Is it happening at the level of the physical mechanics of our eyes? Is it all in our heads? Has the moon moved to be physically closer to the Earth? Um probably not that one- and as you can see in the photo below- it IS an illusion, captured only by our eyes/brains. It's one of my favorite mysteries, and one that has been around as long as we have been looking at the moon (which is a pretty long time).

Moon rise in Seattle- photography can’t capture the moon illusion!

(photo by Shay Stephens January 30, 2002)

The moon will be ginormous tomorrow night. The little squiggly red underline tells me that my spell checker thinks that ginormous is not a word, but according to the Oxford English Dictionary, it has been around since 1948. Back to the point- it will be huge. This is because it is the full moon closest to the summer solstice, which means it will be lower in the sky (because it is opposite the sun and the sun is highest in the sky... you know, the NASA article explains it better). If you have clear skies, be sure to check it out.

Enceladus Is the New Hoth

Image: NASA/JPL/Space Science Institute

So the ice volcanoes continue to be intriguing! It seems that the general consensus is that Enceladus is, in fact, the source of Saturn's gossamer "E" ring. From the Cassini website:

"Saturn's remarkable E-ring is the largest planetary ring in our solar system, spanning all the way from Mimas' orbit to Titan's orbit, about 1 million kilometers (621,370 miles). It is by far the most extended ring around Saturn.

"Until recently scientists assumed that the dust at Enceladus was produced by a process similar to that observed at the Galilean moons of Jupiter: micrometeoroids striking the moon's surface blasting dust particles loose. However, the Cassini data show that the E ring is being replenished not only by dust particles from micrometeoroid hits on the surface of Enceladus but also from grains expelled from possible vents located in the south polar region. The possibility of vents is revealed by a higher surface temperature detected by Cassini's composite and infrared spectrometer, which detected temperature differences at the south pole."

Image: NASA/JPL

For years, we have heard about the moons of Jupiter, particularly the Galilean Satellites: Io, Europa, Ganymede and Callisto. Io is a volcanic moon, Europa is an ice moon that may hold a salty sea beneath its surface (and some speculate that it is one of the most likely places in the solar system where we might find life). With Cassini's arrival at Saturn on July 1, 2004, we have heard plenty about its incredible satellites- Rhea, Dione, HyperionMimas, Iapetus... The Huygens probe has given us pictures of Titan that have stoked the imaginative fires. We have seen a landscape that looks like shorelines, cliffs, and rivers. People have speculated that it might be an active place full of volcanism, and (of course) life. Titan has brought up more questions than answers- are those features really shorelines? Is there really a methane sea that is replenished by "rain?"

Now Enceladus has given us an amazing picture: scientists expected to find ammonia in the ice volcanoes. Ammonia would help keep the water in a liquid or gas state at lower temperatures. So far, they have not found any! Additionally, this moon has the highest albedo (99%- the same value as fresh ice) of any body in the solar system. This means that of all the radiation to hit the surface, 99% of it is reflected. Enceladus, it turns out, is a bright, giant snowball, where it may even snow (hence the Hoth reference. For the Star Wars illiterate, Hoth is the ice planet that hosted the rebel Echo Base (and the AT-AT walker battle scene) in "The Empire Strikes Back")! And (the speculations fly), if an energy source beneath the surface is warm enough to melt the ice, perhaps it is warm enough to support life..? What a much more complex picture we have of our solar system! I remember my sixth grade science teacher telling us that scientists know for a fact that there is no life in the solar system outside of this planet. Now we don't seem to be so sure.

By the way, there is a really interesting video on how Saturn's moons interact with its rings here.