Happy Solstice!

The Beginning of a New Year

Well, the world hasn’t ended, although I hear a lot of people are still writing “Baktun-13″ on their checks. But, you’ll be happy to know that our planet didn’t get hit by a rogue planet, or get eaten by space dinosaurs, or get blasted with a cosmic beam from the center of the galaxy, or any of the other threats that were getting tossed around the Web for the past few years as predictions of what would happen when the old Maya calendar flipped over from the end of one Long Count to the beginning of a new one. So, today (for Maya people) is 13.0.0.0.o — which kind of looks like a computer IP address. Well-played Maya!  Well-played!

What Earth’s solstices and equinoxes look like from space. Courtesy NASA.

However, another useful thing to know is that today is the December solstice. It’s the day when the Sun reaches its most southerly declination (position in the sky) throughout the year.  For folks in the northern hemisphere, it’s the first day of winter. People in the southern hemisphere are celebrating summer!

From here on, the Sun will appear slightly higher in the sky each day until it reaches its most northerly point on June 21, 2013.  This apparent “motion” of the Sun north and south is actually something you can measure throughout the year.  Find a convenient place on the horizon and watch where the Sun sets or rises. Note that point and do the same thing each day (or every few days).  You’ll notice that the Sun does traverse the horizon throughout the year.  Why does this happen?

The answer: because Earth is tilted on its axis. It’s tipped over by 23.5 degrees from the plane of its orbit around the Sun. During some parts of its orbit, Earth’s north pole is pointed toward the Sun and then the Sun appears farther north. For northern hemisphere folk, this is when we get spring and summer, and southern hemisphere people experience fall and winter. During other parts, the north pole is ponting away, and then it appears farther south in the sky.  In the north we have fall and winter, and in the south, we have summer and spring.  The sunrise and sunset positions for all of us change throughout the year depending on where the north pole is pointing.

So, the solstice is really just a “stopping” point in the apparent position of the Sun against the horizon. From here on out, it will look like it’s slowly moving north. And, that’s a great reason to celebrate the “new year” that starts with the December solstice. Yes, it’s different from the calendar year change. But, calendars are culturally based constructs that help us tell time and seasons. The motion of Earth around the Sun is what all these calendars are based on  (plus some other interesting things like the orbit of Venus and the phases of the Moon).

Enjoy your solstice, folks!

Saturn Dazzles Again!

Even Shadowed, It’s Gorgeous

Check this image out, folks. Click on it to get the big view.  It’s a backlit, seriously moody view of the ringed planet made by the Cassini spacecraft and released this week by NASA Jet Propulsion Laboratory and the Space Science Institute. It’s a rare sight because it’s not often that the spacecraft’s orbit takes it to the precise point where the planet, rings, and Sun all line up perfectly to deliver a high-quality view of the rings, plus two dots in the lower left that are Enceladus (Saturn’s active moon) and Tethys (another of Saturn’s icy moons). The detail in this image is astonishing. You can see individual rings in the system, and if you peek closely, you can see them in the gaps as well.  The shadow of the rings on the planet’s cloud tops is especially amazing.

Saturn was one of the first planets I saw a picture of when I was growing up. We had a book about space in the house and when I laid eyes on that weird ringy place, I was hooked!  A bunch of years later, I found myself at JPL during the Voyager 2 encounter with Saturn, covering the event for a newspaper story.  It was even more amazing to me than that first glimpse I had as a child. Pictures like this continually reinforce for ME that the universe is an amazing place that we need to keep exploring!

Holiday Greetings

One of many cool holiday cards using Hubble images! Courtesy STScI.

For those of you still looking for great images to put on your holiday newsletters or greeting cards, this Saturn image is a pretty good candidate. There’s also the highly popular Hubble Holiday Greeting Card page. It’s chock full of 38 nicely designed cards using Hubble Space Telescope images you can simply download and use for your greetings.  I have a hard time deciding which ones to use, so for some years I’ve used every one of them.

I’ve seen people also make up their own cards using images from Spitzer Space Telescope, Chandra X-ray Observatory, and the Mars Curiosity rover, and many others. There’s some gorgeous artwork out there, provided by the cosmos and your tax dollars! So, check it out and be creative!

A Mini Nile on Titan

Cassini’s Latest Find on Titan

A river and delta system on the surface of Saturn’s largest moon, Titan. Courtesy NASA/ESA.

The hits just keep on coming for the Cassini Solstice mission (a joint effort between NASA and the European Space Agency). This time it has sent back a radar image of what looks like a miniature version of Earth’s Nile River delta. It stretches across more than 400 kilometers (about 250 miles). Some kind of liquid is flowing through it, and scientists suspect that it is following along the boundary of a fault (a crack) in the surface. The river empties out into a Titan sea.

Titan is an interesting place. It’s got liquid flowing across its frigid surface, as well as lakes and small seas. Planetary scientists think the liquid that cycles from surface to the atmosphere and back again contains hydrocarbons such as ethane and methane. That’s not all that weird, really. Early Earth may have had a similar environment before things settled out some 4 billion years ago. What this image, and the many other images and observations about Titan tell us is that this is a lively world — it has activity on its surface, and there’s clearly something going on inside this moon that keeps things bubbling along. It experiences seasons, something that astronomers had not expected to find when they sent the mission.

The Cassini Solstice Mission is one of the great success stories in planetary exploration. It was launched as Cassini-Huygens in 1997 and has been tracing an orbital mission through the Saturn system ever since its arrival in 2004. It finished its initial four-year-long mission in 2008 and has been extended twice to continue exploring Saturn, its moons, and rings. It dropped the Huygens lander to the surface of Titan and that gave us our first in situ look at this once-mysterious moon.

The current mission goes through September 2017 and was renamed Cassini Solstice because it will have observed one complete turn of the seasons by May 2017.  It arrived just after Saturn’s northern winter solstice, hence the name.

Cassini’s greatest hits include the discovery and continual study of jets fountaining away from the moon Enceladus. This tiny world has a deep ocean that is kept warm by tidal heating (created by a tug of war between the gravity of Saturn and its outer moons, with Enceladus caught in the middle). The material spraying out from Enceladus has traces of organic chemicals in it, which suggests that Enceladus could be a place where primitive life could form (or may have already).

Saturn itself continues to be a target for the mission. Planetary scientists hope to use mission data to get a clearer picture of the gas giant’s internal structure, and gather more information about its atmosphere.

Want to know more about Cassini and its explorations? The Cassini Solstice Mission has a marvelous Web site where you can find out about the spacecraft, the science, and see many gorgeous images of the Saturnian system. Check it out!