Astronomy.com blog : Rich Talcott

August 2009 web extras for magazine subscribers

Karri Ferron — Tue, 23 Jun 2009 21:30:00 GMT

Now that the August 2009 issue of Astronomy is in the mail or already in hand, we’ve updated Astronomy.com with our newest web extras to give subscribers exclusive complementary information to this special issue about our return to the Moon.

Take a sneak peek inside the August 2009 Astronomy magazine.

If you subscribe to Astronomy, make sure you’re registered with Astronomy.com so you can access these great extras.

Here are this issue's highlights:

Senior Editor Richard Talcott shares a NASA video animation preview of the Constellation program that will put humans back on lunar soil in “Return to the Moon.”

Associate Editor Daniel Pendick explores the opinions on NASA’s concept of “Moon first, then Mars” in “Should we go to the Moon first?”

Pendick also explains the uncertain effects of long-term exposure to space radiation and low gravity in “What are the health risks of a Mars mission?”

Senior Editor Michael E. Bakich offers an in-depth preview of the LRO and LCROSS missions that jointly launched June 18 in “NASA's next Moon mission.”

Pendick answers the “Ask Astro” question: “How warm does it get on Mars?”

And I’ve included a few more Q&As with Frank Shu and Joan Najita in “Astro Confidential: Extending the conversations.”

Of course, we’ve also posted “Bob Berman’s Strange Universe,” “Glenn Chaple’s Observing Basics,” “Stephen James O’Meara’s Secret Sky,” and “David Levy’s Evening Stars.” There are also August’s “The Sky this Month” and five “Ask Astro” questions.

Related:

Astronomy.com's Lunar Reconnaissance Orbiter mission page

Northeast Astro-Imaging Conference 2009 draws record attendance

Rich Talcott — Wed, 22 Apr 2009 15:44:00 GMT

Special post from Imelda B. Joson and Edwin L. Aguirre

In the years since its inception, the Northeast Astro-Imaging Conference (NEAIC) has evolved into the largest gathering of its kind on the East Coast. Astrophotography aficionados from North America, Europe, and Asia have attended or spoken at the 2-day conference, held each year at Rockland Community College in Suffern, New York.

“This year’s NEAIC was a resounding success,” said Jim Burnell, who, together with Bob Moore, Mike Peoples, and members of the Rockland Astronomy Club, organized the event that took place April 16 and 17. “More than 130 people registered for the conference, the largest to date. More than 20 manufacturers exhibited their latest astroimaging gear, and over $5,000 worth of products were given away as door prizes.”

The talks, workshops, and posters covered a diverse range of imaging topics designed to help backyard observers of all ages and at every level of experience overcome hurdles that prevent them from capturing fine astrophotos.

The program featured Tony Hallas (who discussed electronic noise in CCD cameras), Gary Honis (modifying and cooling digital SLR cameras), Dave Snay (introduction to astroimaging and how to choose a mount), Doug George (workshop on MaxIm DL), Steve Mazlin (remote imaging), Sheldon Faworski (choosing a telescope for imaging), Mike Unsold (Images Plus workshop and how to control the DSLR remotely), Imelda Joson (how to get your images published), and Olivier Thizy (low- and high-resolution amateur spectroscopy).

Other speakers included J. P. Metsävainio (3-D image processing), Jim Burnell (choosing a camera for imaging), Jerry Lodriguss (processing DSLR images), Warren Keller (choosing imaging software), Steve Walters (workshop on CCDNavigator), Peter Ceravolo (telescopes for “monster” CCDs), Warren Keller (Photoshop techniques), and Alan Holmes (SBIG’s new differential guiding system).

A new feature this year was a live, remote-imaging session demonstrated by Mazlin on Thursday evening using a telescope in the Andes Mountains in Chile.

NEAIC participants were also given tickets to the Northeast Astronomy Forum & Telescope Show (NEAF), one of the largest astronomy shows in the U.S., held that weekend at the Rockland Community College.

For more information about next year’s NEAIC, visit www.rocklandastronomy.com.

Related:

Online Reader Gallery — Images from astrophotographers all over the world

New videos: Springtime observing targets

Rich Talcott — Tue, 10 Mar 2009 21:10:00 GMT

In this video, I discuss the objects you can see with your naked eyes and binoculars in this spring’s sky. The season offers several bright planets, notable constellations, and bright deep-sky objects. You can locate all the night-sky sights I talk about with Astronomy.com's interactive star chart StarDome.

Watch the video, "Observe easy-to-find objects in the spring sky."

Venus

As darkness falls during the first half of March, your eyes will be drawn to the western sky. In the deepening twilight, Venus gleams like nothing else. You won’t have any trouble identifying the brilliant planet, which glows brighter than any other point of light in the sky. Venus passes between the Sun and Earth in late March, and will reappear in the east before dawn by mid-April.

Saturn

Beautiful Saturn also lies in the evening sky, although it doesn’t stand out like Venus. Look for Saturn among the background stars of Leo the Lion, where it glows as bright as that constellation’s brightest star, Regulus. Saturn will remain in the evening sky until late summer.

Mercury

Elusive Mercury puts on its best evening show of the year in the last 10 days of April. Watch for a bright point of light low in the west-northwest 30 to 45 minutes after the Sun sets. The easiest evening to spot it will be April 26, when it lies directly below a crescent Moon.

Jupiter

Meanwhile, Jupiter appears conspicuous in the morning sky during April and May. Look for it in the southeast around the time twilight starts to paint the sky. Only the planet Venus shines brighter than Jupiter.

The Big Dipper

Spring’s starry background has its own charm. Those of us in the Northern Hemisphere have a signpost in the spring sky: the bright asterism of the Big Dipper. Seven bright stars in the constellation Ursa Major the Great Bear create the Dipper’s shape. On spring evenings, the Dipper stands nearly overhead, at the center of this star chart.

Use the two stars at the end of the Dipper’s bowl, called the Pointers, to lead you to the North Star, Polaris. Extend the line between the Pointers (which lie at the bottom left of this photo), and extend it about five times that distance. Polaris is the brightest star in the Little Dipper and forms the tip of its handle.

Head back to the Big Dipper and take a close look at the middle star in the handle, called Mizar. If you have decent eyesight, you should see a fainter companion star just to its east. If you can’t see it, turn your binoculars on this star and its double nature will stand out.

Now, let’s use the Big Dipper to find some of spring’s other celestial delights.

If you follow the arc of the Dipper’s handle away from the bowl, you’ll soon arrive at Arcturus — the brightest star in the spring sky. Continue the arc about an equal distance and you’ll find Spica, the brightest star in the constellation Virgo. Spica dominates this sprawling constellation, and has the distinction of being the bluest of all 1st-magnitude stars. When it comes to stars, blue means hot, and Spica’s surface blazes at a temperature nearly four times hotter than the Sun.

Next, head back to the Big Dipper, and imagine poking a hole in the bottom of its bowl. The water would flow out and fall on the back of Leo the Lion. Leo consists of two distinctive sections: A group of six stars on the right that looks like a backward question mark, and three stars on the left that form a right triangle. Remember that Saturn augments the Lion’s shape this year, just below the pattern seen here.

Our final stop in the spring sky lies one constellation west of Leo, in the faint group known as Cancer the Crab. Smack in the middle of this constellation lies perhaps the spring sky’s finest binocular target: the Beehive star cluster (M44). On exceptionally clear nights from a dark site, you might spot the Beehive with your naked eyes. Binoculars reveal the cluster’s true nature. Through 10x50 binoculars, you should be able to see at least two dozen stars packed into a circle some three times wider than the Full Moon. It’s a sight you won’t soon forget.

We’ve created two more videos like this one to help you enjoy everything the springtime sky has to offer.

Astronomy magazine Senior Editor Michael Bakich’s video “Springtime observing for small telescopes” highlights this year’s best springtime targets you can see with a 4-inch or smaller telescope.

Astronomy magazine Editor Dave Eicher’s video “Springtime observing for large telescopes, 2009” highlights this year’s best springtime deep-sky objects you can see with an 8-inch or larger telescope. Both of these videos are available for Astronomy magazine subscribers at Astronomy.com/videos.

I’ll be back again this summer to talk about what’s on view during the warmest nights of the year.

The perfect deep-sky observing guide

Rich Talcott — Wed, 04 Mar 2009 20:34:00 GMT

A dark night and a small- to medium-sized telescope are all you need to enjoy the deep-sky splendors that dot Earth’s skies. Oh, and one other thing — a good guide that describes what to look for and what you’ll see through the eyepiece.

We’re excited to offer one of the best deep-sky observing guides of the past decade. Author and Astronomy magazine Contributing Editor Tom Polakis created an exclusive series of articles for the magazine called “Celestial Portraits.” The series ran in Astronomy from April 1998 through March 2004, and now you can purchase and download the whole series in digital format.

In each of the 45 articles, Polakis features one or more constellations and the sparkling star clusters, glowing gas clouds, stately galaxies, and other deep-sky objects that backyard astronomers can’t get enough of. In addition to detailed descriptions, each article features great amateur photos and a star chart that pinpoints every object’s location.

We put together 11 packages, and each contains four articles from the series.

To browse the catalog, visit Astronomy.com’s new “Constellation Observing” section. There you can find your favorite constellation, preview each article, see what constellations each package contains, and download “Orion the Hunter” for free.

Keep your eyes peeled for more downloadable articles just like these from Astronomy magazine.

Spot and follow the year’s brightest comet with Astronomy.com

Rich Talcott — Wed, 11 Feb 2009 19:09:00 GMT

Comet C/2007 N3 (Lulin) remains on track to be the brightest comet of the year. It should peak around 5th magnitude during the second half of February, when it will slide past Spica, Saturn, and Regulus. To track the comet from your location as it crosses the night sky, check out Astronomy.com's interactive star chart — StarDome.

To find and track Comet Lulin with StarDome:

On the lower right of the dome display, under "Options," click the Display... pull-down menu.
Select Comets from the Display... pull-down menu and make sure a check mark appears next to Comets
Click the Show names... pull-down menu
Select Comets from the Show names... pull-down menu
Under "Date and Time Settings," highlight the hour, and click the UP arrow repeatedly. Depending on your location, you should see "C/2007 N3 (Lulin)" written in a teal-colored font, enter the dome display at about 23:00 local time.
Adjust the dates to watch Lulin's path across the sky throughout the month.
To see Lulin in relation to Spica, Saturn, and Regulus, be sure Planets and Bright Stars are selected under the Show names... pull-down menu.

Mercury turns its other cheek

Rich Talcott — Wed, 29 Oct 2008 19:06:00 GMT

Earlier today, planetary scientists discussed preliminary findings from the MESSENGER spacecraft’s second flyby of Mercury. The October 6 encounter revealed about 30 percent of the planet previously unseen by spacecraft — an area larger than South America.

MIT researcher Maria Zuber spoke about results from the laser altimeter used to measure topography. Her biggest surprise: The thin strip of area surveyed seen during the January flyby.

Brian Anderson from Johns Hopkins University Applied Physics Lab noted that the magnetic field seen this time around nearly matches that seen in January. This implies a symmetric magnetic field whose axis tilts no more than 2 percent to Mercury’s rotational axis.

Mark Robinson of Arizona State University discussed a small number of the 1,287 images MESSENGER returned. They included some color-enhanced views that show apparent widespread regions of material excavated from below the surface. In these enhanced images, the material appears blue.

Watch upcoming issues of Astronomy magazine for comprehensive coverage of the second MESSENGER flyby. As always, check Astronomy.com/News for mission updates.

Astronomy previews the Large Hadron Collider's big day

Matt Quandt — Tue, 09 Sep 2008 19:47:00 GMT

I sat down with Astronomy magazine Senior Editor Rich Talcott to learn more about the Large Hadron Collider (LHC) and its September 10 test.

For additional background information on the LHC, visit Astronomy.com.

UPDATE: LHC successfully passed its September 10 test.

Here is the transcript of my conversation with Rich:

What is the Large Hadron Collider?

Well the LHC, as the name implies, is something that’s big, that’s going to collide elementary particles called hadrons. And basically what these guys are are subatomic particles that consist of quarks and are held together by the strong nuclear force. The LHC is going to collide hadrons at tremendous energies.

The most well known hadrons are neutrons and protons. And what the LHC is going to do mainly is collide protons together at stupendous speeds.

The particles are going to be traveling around the 17-mile [16.57 miles] circumference at within one millionth of one percent of the speed of light. We’re talking 99.999999 percent the speed of light.

At those speeds, there’s going to be a tremendous amount of energy released whenever the protons collide. The ring actually has six different experiments that are going to be looking for different results when these particles collide.

The protons make 11,000 trips around the 17-mile loop every second. So it’s 11,000 revolutions per second.

And when it’s fully functioning, they’ll be colliding 600,000,000 protons together at a time. So we’re talking a large number of high-speed protons coming together.

To make this device work, it needs to be cooled to a very low temperature. So it’s 1.9 Kelvin above absolute zero, which means 1.9 degrees Celsius above absolute zero. So it’s extremely cold magnets that are going to keep the particles moving around the circle so that they can be collided together.

Also as you might expect the particles moving around inside this thing would naturally run into air molecules and create collisions as well. So one of the things that they’re going to do is create a vacuum that’s equal to interplanetary space, or actually about 10 percent the density of the Moon’s atmosphere. It’s going to be an extremely good vacuum inside here so that the protons don’t interact with all sorts of other things before they run into each other heading in opposite directions.

What do scientists hope to learn from the LHC experiments?

There are two different ways that scientists are looking at the LHC and what it can do for them. Both physicists and cosmologists are really interested in what’s going on here. And it’s high-energy physicists that get the big play here. One of the particles that scientists believe exists, but has never been detected before, is called the Higgs boson, and it’s also been called the “God particle” because it has such special properties.

Among them being the fact that a lot of scientists think this is the particle that confers mass on every other particle in the universe. So scientists are deeply concerned about finding this particle to learn its properties to see if there may be different versions of this particle out there. We haven’t had an experiment yet that’s been able to reach the energies necessary to create these particles, and so that’s one of the hopes here.

Some people may wonder how colliding particles like protons together actually could create anything because most of the time collisions tend to destroy. But if you remember back to Einstein’s famous equation, E=mc^2, matter and energy are just two different versions of the same property essentially. And so when you’re colliding these particles together the tremendous energy can create matter, and that’s what the scientists are hoping for.

So LHC could reveal God? [laughter]

Well, one of his particles anyway.

The other reason that the Higgs boson is so important to physicists trying to study how the universe is put together is that it’s an essential ingredient in the standard model that physicists have developed to describe how matter works.

These kind of go together into what are often called the grand unified theories that combine the electromagnetic force along with both the strong and weak nuclear forces. And these three of the four forces in the universe are combined in the standard model, and the Higgs boson is essential to making that standard model work.

If the LHC does not turn up the Higgs boson, then that means physicists have to go back to, if not to square one, at least to a low number square in order to be able to figure out how the universe works.

The other aspect that the LHC is going to look at, or what makes cosmologists perhaps most interested is that the conditions that are going to be created within the LHC are the same conditions that existed very early in the universe back when it was less than a second or so old.

And this is going to be the first controlled experiment that we’ve ever had that is going to be able to look back and see what conditions in the early universe are like. So among the things cosmologists are interested in learning is how come there’s a lot more matter than antimatter in the universe. Theory says there should be equal amounts of both. But because whenever matter interacts with antimatter it turns into energy, there shouldn’t be any matter here in the universe; it should’ve all been exploded into energy. Obviously we do have a lot more matter than antimatter, and so there’s some fundamental difference between matter and antimatter, and one of the things that the LHC may be able to get at is what that difference is.

Another thing that they’re going to be looking for is information about dark matter and dark energy, which together make up about 96 percent or so of the mass and energy in the universe. The LHC is going to be looking for something called supersymmetric particles, which may well have a role to play in dark matter and what that is, and so this is going to try to give astronomers and cosmologists an idea of what a good fraction of the universe is made out of.

One other thing that may help cosmologists out is that some of the particles and conditions created may be enough to see whether space has more than the three dimensions that we’re familiar with.

This is one of the things that string theory, a favorite of science-fiction writers and scientists who like to really think out there. String theory may be a way of combining gravity with the three forces that the grand unified theories attempt to unite. One of the predictions of string theory is that there should be many more dimensions than just the three or four of space-time that we tend to think of here in our universe. If it can get at looking at some of these potential extra dimensions, that may give the first experimental evidence of string theory.

What’s happening September 10?

The next big step in the commissioning of the LHC comes on September 10. They’re going to circulate a beam throughout the 17-mile-long tunnel.

The actual first high-energy collisions aren’t going to happen until it’s officially commissioned, and that’s on October 21. Or at least, that’s the current date. So we still have more than a month left before they start colliding these protons at super-high energies to see what comes out.

So September 10 is a test of their being able to circulate the beams and getting them up to the speeds that they want to.

Which is probably, just throwing out a number, 9/10 of what they want to do to make sure everything’s working. If they can circulate a beam, they can presumably circulate them in both directions and collide them. So it’s kind of a minor step beyond being able to circulate the beam at high speeds.

How do they produce the particles?

There’s a linear accelerator that injects the particles into the circular ring, and so it starts the particles at very high energies. The magnets then speed up the protons and keep them moving around the circular path.

They start with high-speed protons that get sped up inside the ring.

Have these experiments ever been done before?

This is easily the highest energy experiment that’s been done, and there have been other experiments that have gone on that have reached lower energies and that have found out much of what’s going on in the universe. So we have a lot of good evidence that the standard model is true based on what earlier experiments have shown. But we haven’t been able to get to the energies needed to see the Higgs boson and to see some of these other effects, so we’re trying to get up to the energy needed to be able to see the next stage of the evolution of the models and the experiments.

So it could confirm what we’ve learned, or it could provide evidence that forces physicists to go back to square one?

It’s always interesting. If scientists knew what an experiment would show, there wouldn’t be any need to run the experiment. This experiment is like all others — basically, we don’t know for sure what it’s going to show, so one of the things is if it finds the Higgs boson and it has the properties physicists expect, then that goes a long ways toward confirming the standard model of particles.

But if the Higgs boson doesn’t exist at what scientists expect, then they’re going to have to go back and try to figure out where the Higgs boson may fit in, if it has different properties, or if they don’t find the Higgs boson, how matter is actually put together and what causes mass in the universe because that’s what the Higgs boson is supposed to be able to do.

Where did the funding come for LHC?

There are actually more than 8,000 scientists and more than 80 countries involved in the LHC and something like 400 universities, so the money came from all of these participants in the project.

Is it the largest collaborative science experiment in the history of science?

Yeah, I think that would be fair to say.

Along the outside of the ring, there are six different experiments set up so it’s not a single experiment; there are going to be six different experiments looking for different things from the proton collisions. And so, you wouldn’t say all 8,000 people are working on the entire thing. There are lots of sub-disciplines that people are working on or experiments that may not have anything to do with the other experiments.

One of the fun things is looking at the author lists on high-energy particle physics papers and these are going to be ... there have been some high-energy particle physics papers that have more than 100 authors on them, and these won’t be any smaller.

Where does LHC rank in terms of scientific instruments throughout history? Bigger than Hubble?

The amount of data that we’re going to get from the LHC, to put it in perspective, it’s enough that if you put it all on CDs, every year there will be enough CDs to go to the Moon and back twice.

So there’s a huge amount of data that is going to come out of this, and it’s teasing out the small effects from that data that’s going to give us all the knowledge that we hope. It’s fair to say that in terms of the basic scientific knowledge that we can and should get out of the LHC, it’s going to be certainly at least as much as Hubble does, but it’s not going to be in the same sense of pretty pictures of what the universe looks like. The universe of the very small is far different from the universe of the very large, and you may have to be a scientist to appreciate the beauty of the very small.

It’s the first controlled experiment that’s going to be able to look back at what conditions were like very shortly after the Big Bang. So we are going to get a look at the universe’s origins in a way that we haven’t had the chance to do before.

What are the potential dangers of flipping the switch September 10?

You may still run across on the Internet examples of people talking about how Mars at this opposition is going to look as big as the Full Moon. Most of the purported problems that are associated with the LHC kind of fall into that same realm of people taking a little bit of knowledge and using it to advance far beyond what might possibly happen.

One of the things that people have talked about is the production of the mini black holes by the particle collisions, and that’s not totally out of the realm of possibility. The thing about black holes it that they tend to evaporate over time, and the smallest black holes evaporate the most quickly. Any black hole created by these particle interactions would disappear within a small fraction of a second, something along the order of a billionth of a billionth of a billionth of a second. So any of these black holes would evaporate before they would have a chance to start devouring anything around them.

People have talked about [LHC creating] conditions that have never been created before in the universe, or not since the Big Bang, which is not necessarily true. We have things called ultra high-energy cosmic rays that rain down on Earth’s atmosphere and these things, believe it or not, have energies far greater than the energies that we’re going to have in these collisions.

Something on the order of a million times stronger; we’ve seen cosmic rays with those energies. Those cosmic rays run into molecules in Earth’s atmosphere and so far haven’t created any black holes that have swallowed Earth or created any strange particles that have developed into anything that could threaten Earth. The fact that the universe is creating experiments similar to what the LHC is going to do, just not in a controlled way, is the best proof that we don’t have anything to worry about here.

Back when they exploded the first atomic bombs in the 1940s, there were a few scientists that predicted that it could launch a chain reaction that would essentially ignite the atmosphere of Earth and burn out all the oxygen in Earth’s atmosphere. That probably had a bigger chance of coming true than this does.

Michio Kaku, a theoretical physicist and someone who has written for Astronomy before, said “These things may be possible, but, technically, so is the fact that the LHC could create a fire-breathing dragon, and they’re about equally probable.”

Clear skies for totality

Rich Talcott — Wed, 06 Aug 2008 16:15:00 GMT

Twilight ringed the horizon above the Ob Sea during the August 1 total solar eclipse. Rich Talcott photo

The weather forecast for August 1 in Novosibirsk, Russia, didn’t look promising. On the evening of July 31, the most favorable prediction called for partly cloudy skies, while the more pessimistic predicted a 70 percent chance of rain. Fortunately for Astronomy Editor Dave Eicher and me — and more than 150 fellow eclipse chasers with our MWT Associates eclipse tour — the forecasters proved to be well off the mark.

Our group was perched on the shores of the Ob Sea just outside Novosibirsk. By the time we arrived at our eclipse site in mid-afternoon, the skies already were mostly clear. And conditions only improved by the time the Moon began to cover the Sun. As shadows sharpened and the Sun waned to a thin crescent, the only significant clouds in the sky were clustered low in the north — far away from the Sun’s position.

Those clouds served as a harbinger of totality. As the Moon’s shadow approached us, the clouds turned from pinkish-white to dark blue, signifying the shadow’s imminent arrival. Then, before you could say “diamond ring,” the Sun’s photosphere winked out and totality began.

Gasps echoed along the shoreline as the Sun’s corona burst into view. With solar activity now at a low ebb, several coronal streamers stretched far above the Sun’s equator, while delicate polar brushes arced above the polar regions. Meanwhile, a fiery solar prominence appeared near the 2 o’clock position. And not far to the Sun’s east, the bright planets Mercury and Venus blazed away.

Two minutes and 20 seconds isn’t long, however, particularly when you’re talking about a total solar eclipse. Before we knew it, a beautiful, long-lasting diamond ring announced totality’s end. Although the main event was over, it took a long time for the exhilaration to fade. Now, we can let the excitement build slowly toward next July and the 6-minute eclipse in China.

The Moon joins the Seven Sisters

Rich Talcott — Fri, 04 Apr 2008 16:30:00 GMT

On Tuesday evening, April 8, you can experience one of the most beautiful events the sky can deliver. Head outside no later than an hour or so after sunset (around 8:30 P.M. local daylight time) and look to the west. Your eyes should land immediately on the slender crescent Moon, oriented with its cusps standing nearly straight up from the horizon. Point your binoculars at the Moon to reveal a stunning sight: the bright Pleiades star cluster (M45) sparkling like a clutch of tiny diamonds accenting the primary jewel.

When you first gaze at the Moon, you may see only its brightly lit crescent. Look a little closer and you’ll see an ashen light filling out the “dark” part of the Moon’s disk. This light comes from sunlight reflecting off Earth’s dayside up to the Moon and back to us. Literally, the Moon is bathed in earthshine. If it appears particularly bright, you should see some dark lunar “seas” and bright craters. These will stand out more if you observe through a small telescope.

This conjunction will show you how fast the Moon moves against the starry background. Around 8:30 P.M. from central North America, Earth's satellite sits to the Pleiades’ right. An hour later, the crescent Moon covers some stars at the cluster’s upper right. And an hour after that, the Moon lies directly above the Pleiades.

Although the Moon and Pleiades appear close to one another in our sky, a lot of space lied between the two. The Moon is only a stone’s throw from Earth: about 225,000 miles, or 1.2 light-seconds. The Pleiades, on the other hand, lies more than 2 million billion miles from Earth, or some 440 light-years.

That distance has had its ups and downs. Until 1997, most astronomers thought the Pleiades were about 440 light-years away. That year, the European Space Agency (ESA) claimed it was some 10-percent closer, or a little under 400 light-years. This estimate came from ESA’s Hipparcos satellite, which was supposed to deliver the most accurate stellar distances yet.

Fortunately, the Hubble Space Telescope came to the rescue. Using the orbiting telescope’s ultra-precise Fine Guidance Sensors, Hubble scientists pinned down the Pleiades’ distance at 400 light-years. Early data analysis on Hipparcos observations contained a small but noticeable error when lots of bright stars contaminated the field. As you gaze at the Moon and the Pleiades this Tuesday, think about how far in the background the cluster’s stars really are.

In need of some respect

Rich Talcott — Thu, 13 Mar 2008 19:07:00 GMT

It seems to me that Saturn’s moon Rhea is a leading candidate for Rodney Dangerfield of the solar system. I tell you, it doesn’t get much respect. Even in the Saturn system, where Rhea is the second-largest moon, it ranks pretty low. You hear about Titan, with its thick atmosphere and methane lakes. Enceladus is known for its liquid-water geysers and Iapetus for its strange black and white hemispheres. Even tiny Mimas, with its cute “Death Star” crater, gets more ink than Rhea.

Maybe all Rhea needs is a better publicity agent. If so, help may be on the way. At this week’s Lunar and Planetary Science Conference in Houston, Roland Wagner of the German Aerospace Center in Berlin spoke about the Cassini spacecraft’s latest exploration of Rhea’s geology.

Rhea’s complex geology shows up nicely in this image, taken by the Cassini spacecraft when it passed close to Saturn’s moon last August. NASA/JPL/SSI

Wagner’s team analyzed the moon’s crater distribution and found that the heavily cratered terrain on Rhea’s leading hemisphere has an age of 4.0 to 4.2 billion years. Rhea does have some young features, however. In particular, a 30-mile-wide (48 kilometer) crater with bright rays which may be barely several million years old. The rays and secondary crater chains extend hundreds of miles from the crater.

This youthful feature may be related to one of the most surprising solar system findings of the past decade. Just last week, Cassini scientists announced in the journal Science that Rhea has a ring, mimicking the most-storied feature of its host planet.

Geraint Jones of Mullard Space Science Laboratory at University College, London, led the team that discovered a ring embedded within a broad debris disk surrounding Rhea. The disk spans several thousand miles, and consists of objects that likely range in size from pebbles to boulders. The team used two Cassini instruments to detect drops in the number of electrons on both sides of Rhea. “Seeing almost the same signatures on either side of Rhea was the clincher,” Jones says.

Since the discovery, Cassini scientists have run numerical simulations showing that Rhea could maintain rings for a long time. That ties back to the bright ray crater on the moon’s surface. Perhaps the impact that formed this crater also ejected the ring material into orbit. “No one was expecting rings around a moon,” Jones says. Maybe this unique trait will finally earn Rhea the respect it so richly deserves.