Solar System
esiegel | October 5, 2009Mercury, the closest planet to the Sun, never really has had a great picture taken of it. There are a number of reasons for this, such as:
It never gets more than 28 degrees away from the Sun, meaning we get two hours after sunset -- max -- to look at it.
Because the sky is still light, it's very hard to get a good resolution image from the ground.
Because of its proximity to the Sun, operators refuse to point space telescopes (like Hubble) towards Mercury, for fear of frying the telescope.
Mercury is far away and tiny, making for a disastrous photographic combination.
From Earth, this is…
esiegel | October 5, 2009Though my soul may set in darkness,
It will rise in perfect light,
I have loved the stars too fondly
To be fearful of the night. --Sarah Williams
Everyone knows how you see things during the day: sunlight makes it possible. Delivering huge amounts of visible light to the entire "day" side of the planet, everything becomes illuminated to human eyes.
But things change rapidly once the Sun goes down. Even with a full Moon in the sky (like last night), the amount of light reaching the Earth at night is over 100 trillion times less than during the day.
Still, we have a great pair of eyes, and…
esiegel | October 2, 2009When I was a kid, Mercury and Pluto were the bookends of our Solar System. The two smallest planets, one of them was distant, icy, and raw, and the other was close in, speedy, and overcooked. One of them had the New Horizons mission planned for it, and the other had the Messenger mission.
Only one of them is still a planet, but Messenger just passed by Mercury for the third (and final) time. In early 2011, Messenger will settle into orbit around Mercury. Until then, you'll have to content yourself with these brand new images -- many just released today -- from Messenger's flyby of Mercury…
esiegel | September 24, 2009When I was first learning about the science of the Moon, there were a few basic facts that everyone got right. The Moon has practically no atmosphere, as when sunlight hits the Moon, it very quickly can give individual molecules and atoms enough energy to achieve escape velocity. We thought the same thing was true for any water on the Moon; sunlight would kick the water molecules so hard and so often that the molecules wouldn't remain on the Moon for very long, and therefore it would be completely dry.
A watery Moon? Possible at all? Well, there was one hope. You see, the Earth rotates on an…
esiegel | September 8, 2009Sure, we're all familiar with sunsets, and how they appear to turn the entire sky close to the horizon red at night.
But it turns out it isn't just the Sun, and it isn't just the sky. If you look at the Moon at either Moonrise or Moonset, guess what color it appears to be? (Even in urban settings!)
Too difficult to tell? Let's find you a better picture done with time-lapse photography.
What's going on to cause this? Why do things which aren't normally red appear red when you look at them on the horizon, from the Sun to the Moon to the sky itself?
This is all the atmosphere's fault. After…
esiegel | September 3, 2009One of the things I always wondered was why Galileo's Eppur si muove! (And yet, it moves!) was such a big deal. Yes, he was talking about heliocentricity, and the Earth moving around the Sun instead of the other way around.
But I was a little bit puzzled. Why, after all, would the Earth moving be such a revolutionary idea? Every night, if you look up and watch the skies over time, you'll see something like this:
The sky rotates! Not only do the stars in the night sky rotate, but the Sun's path through the sky also goes along one of the same paths that the stars do, as does the Moon. (For a…
esiegel | August 31, 2009Okay, as many of you had heard, I've got a new job as a full-time Professor. And not only am I pretty excited about it, I thought I'd share with you one of the more interesting things I taught on the first day.
I got this idea from talking to Michael, the chair of the department (and this is not the first time he's taught me something neat). Chances are, if you're in a classroom, that one thing everyone has is a piece of paper.
If you folded this piece of paper in half, it would now be twice as thick as it was before:
So my question is this: how many times would you have to fold this…
esiegel | August 26, 2009On Monday, I posed a question to you as to why, when you photograph the Sun at the same exact time every day for a year, you get something that's shaped like a figure 8, like so:
Image credit: Tunc and Cenk Tezel.
We got a good number of thoughtful comments, many of which are on the right track, and many of which have some misconceptions. Let's clear them up, and then let's give you the explanation of what gives us our figure 8, and why other planets make other shapes.
What does the analemma look like at other places on Earth? You can see, above, that (from the ruins) the above analemma is…
esiegel | August 24, 2009I'm trying something new here: I'm going to give you a little bit of information and a teaser, and we'll see -- in the comments section -- whether any of you can figure it out.
Imagine that you went outside, each and every day at the same time, and mapped the position of the Sun. What would you see?
Image credit: Astrosurf.
Doing this -- taking a snapshot of the Sun at the same exact time from the same exact place on different days -- gives you what's called an analemma. Now, on Earth, the top of the analemma happens during the Summer Solstice, the lowest point of the analemma happens…
esiegel | August 17, 2009About four months ago, the Mars Rover Opportunity was driving around Mars at about 50% power, as five years of accumulated Martian dust on its solar panels was disastrously affecting its ability to acquire power:
But a fortuitous, powerful gust of wind knocked much of the dust off, boosting Opportunity's power by about 40%. Because of this, Opportunity was able to continue making its way towards Endeavor crater -- the largest Martian crater that will ever be examined by any rover -- with an added power boost:
Well, a few weeks ago, Opportunity was cruising along the Meridiani Planum when it…
esiegel | August 11, 2009When you go outside at night, on a clear night away from all lights, you see the sky the same way the ancients did: full of stars.
Now, if you looked up periodically, you would find that the sky appears to rotate! Some constellations rise while others set, and one point -- either due north or due south depending on your hemisphere -- appears to not move at all. With the advent of time-lapse photography (and go here for a fantastic video), we can see that the sky does something like this:
So there's some pretty good evidence, right away, that either the Earth is rotating or the entire sky is…
esiegel | August 10, 2009There's a good reason for it, I promise! Allow me to explain. You see, every so often, a comet zooms in from the Kuiper Belt. As it approaches the Sun, it heats up, displaying a spectacular tail.
What is this "tail" actually? It's tiny, tiny fragments of ice and rock that make up the comet. You see, comets are like miniature, frozen planets. The gravity holding a comet together is amazingly weak because they're so tiny. For comparison, a grain of sand on the surface of a comet experiences less than 0.002% of gravity on Earth. This gravity is so small that tiny, micron-sized pieces of dust,…
esiegel | August 6, 2009Every once in awhile, a question makes it to my inbox that's too good to ignore.
A friend and I were joking about being "older than dirt" and he asked a question I thought you might enjoy: "Hey, ask Ethan how old dirt is and how it got here."
You did the smart thing by coming to me, because the alternative is to ask yahoo. (Shudder!) Well, right away, we've got an upper limit, because the entire Solar System is only about 4.5 billion years old. So, there's no way that this:
is any older than this:
Now, you can definitely go looking for the oldest rocks on Earth, and if you look very hard,…
esiegel | July 29, 2009Sure, sure, everyone knows that stars twinkle. You look up at the night sky, and pretty much any star you look at appears to fluctuate in its brightness and intensity very rapidly, giving it a "twinkling" appearance.
Why does this happen? It definitely doesn't have anything to do with the star itself, because "our" star, which you call the Sun, definitely doesn't twinkle the same way:
Not only that, but there are a few objects in the night sky that don't twinkle: the Moon, planets, and satellites.
Why is that? Why do stars twinkle, and nothing else? Well, there were two theories.
One was…
esiegel | July 24, 2009Recently, I expressed an opinion on this site in favor of a manned mission to Mars. I was met with many comments -- both positive and negative -- discussing this position. So I'd like to, first off, find out what your opinions on it are:
I realize that there are many other deciding factors on whether you think the answer should be yes or no, but I'd like you to pick the closest one.
For me, a combination of the first and third reasons are why I am compelled to say yes. This is important, because I freely admit that I believe the scientific merits of a manned mission to Mars are very…
esiegel | July 21, 2009That's right, the absolute best eclipse of our lifetimes is going to occur tomorrow! First off, total Solar Eclipses are rare enough, and spectacular when they happen.
After all, a total solar eclipse allowed us to first test Einstein's General Relativity! A total Solar Eclipse happens when the Moon passes directly in between the Earth and the Sun, casting a shadow on the Earth.
This only happens rarely, for three reasons. First off, the Moon's orbit is not in the same plane as the Earth and the Sun. The Moon's orbit is inclined by about 5 degrees to the plane that the Earth orbits the Sun…
esiegel | July 20, 2009Today: July 20th, 2009. The 40th anniversary of the Apollo 11 moon landing. The very first time mankind walked on the Moon. From liftoff,
to walking down the lunar landing module for the first time,
to some of the most iconic images in all of human history:
It brings up a sense of wonder unlike any other before. This video by the onion is so funny to me because it really does capture that sense of awesomeness, and just how blown away those twelve men who got to walk on the Moon must have been:
And it's 40 years later now. While, scientifically, we understand more about outer space, the…
esiegel | July 17, 2009I'll keep this simple, as you can get longer writeups at Universe Today, Bad Astronomy, and the NASA site, but a NASA spacecraft currently orbiting the Moon just released images of five of the six Apollo landing sites.
Why am I so excited about this? Because you can see the Earth-junk we left there! There's the lunar module from Apollo 11:
the one from Apollo 14 (Apollo 12 was out of the way, and Apollo 13 -- of course -- never made it onto the Moon):
and from Apollo 15:
Apollo 16:
and Apollo 17:
Go back to Apollo 14. There's something spectacular that you can see on the Moon in that…
esiegel | July 10, 2009The inner Solar System is a pretty bizarre place. Think about the giant planets in our Solar System -- the Jovian planets -- that weigh in from tens to hundreds the mass of Earth.
These giant balls of gas are orbited by all sorts of interesting things, from moons so giant that they have their own substantial atmospheres like Saturn's Titan:
to captured Kuiper Belt objects, like Neptune's giant moon, Triton:
to regular natural satellites that formed around the giant planets as they formed, such as Saturn's Dione and Enceladus:
All told, if we look at all the moons in the Solar System, the…
esiegel | July 8, 2009This is the coolest thing online I've seen in a long time. A team of amateur astronomers took over 1000 pictures of tiny areas of the Moon. 288 of them were chosen and mosaiced together. They describe the result far better than I do:
The end result is a high resolution 87.4 megapixel image of the Moon, larger even then previous images taken by some of the world's largest observatories, allowing features as small as 1km to be clearly seen.
This is the world's record for the largest mosaic of the Moon ever made, and it's available for you to view in full detail (!) at their site, Lunar World…