QUEST Community Science Blog Author: Ben Burress

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Far Out, Man: Measuring Astronomical Distances

July 3rd, 2009 by Ben Burress

Centuries ago the stars were believed to reside just beyond the planets of our solar system.It never fails to astound me how big the Universe is—how far away even the nearest stars are, let alone other galaxies scattered from here to near infinity….

How do we know how far away celestial objects are? This shouldn't be taken for granted, as it's not as straightforward as sounding the depth of the ocean floor with sonar, or determining the range to an object by bouncing radio waves off it and timing the reflection.

In fact, we have "pinged” the nearest celestial objects with radar to determine their distances very accurately. Examples are the Moon and Venus, where round-trip lightspeed travel is measured in seconds or minutes.

Before radar, the scale of the Solar System had to be determined geometrically, by observing events like Venus or Mercury transiting the face of the Sun from different locations on Earth and triangulating. Even this technique requires telescopes, which we've had only four hundred years. Before that, figuring out distances to just about everything except the Moon was mostly guesswork. In fact, it wasn't too many centuries ago that the entire Universe was believed to be not much larger than the Solar System—the Sun and it's nine…excuse me…eight planets—as we know it today.

Once the distance from Earth to the Sun was figured out, that length (the "Astronomical Unit”) in effect became a basic measuring rod for working out distances to everything else, by one means or another.

As Earth orbits the Sun, the direction from which we see stars shifts minutely, and we can observe a small change in a star's position compared to the more distant "background” stars. You can see the same effect by holding a finger in front of your face and looking at it alternately with one eye, then the other.

The geometry of this observation is a simple triangle, whose base is the distance between your eyeballs and whose legs are the lines from each eyeball to your finger. By knowing the length of the base, and observing the change in viewing angle against the background, the length of the legs (distance from your eyeballs) can be calculated.

In the case of Earth and a nearby star, the "eyeballs” are the Earth at two ends of its orbit around the Sun (six months apart) and the "finger” is the star.

But this measuring of distance by "trigonometric parallax," as it's called, only works for the nearest stars, as the minute shift in the star's apparent position diminishes with distance.

As astronomers learned more about the distance to nearby stars, they determined how to relate their temperature and mass to their actual brightness, and it became possible to estimate the distance of many stars by measuring their apparent brightness, with an understanding of how the brightness of light weakens with distance.

To measure the depths of space between us and galaxies far, far away, in which individual stars are indistinguishable from the overall galactic glow, we can turn to certain types of supernovae: individual stars that temporarily shine brightly enough to be observed and measured. Like the flare of a match struck in the dark night, the brilliance of the flash reveals how far away the striker stands.

We have built up our knowledge of the Universe's vastness over the past couple centuries, working out the problem from the near to the far. Even as science and technology have made the world on which we live smaller, it has done exactly the opposite to the Universe….




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"Mars Encounter:" An Inconvenient Hoax

June 19th, 2009 by Ben Burress

Mars as seen through Chabot Space & Science Center’s 20-inch telescope near the 2003 close encounter. Credit: Conrad Jung/Chabot Space & Science CenterIf you take away no other message from this blog, just remember this: the planet Mars is NOT passing close to Earth this August and will NOT appear as large as the Full Moon. There; disclaimer delivered.

As August approaches, the ghost of Mars returns to haunt us, in the form of emails and phone calls from people asking if it's true that Mars is about to get closer to Earth than it has been in a gazillion years—so close that it will look as big as the Full Moon.

I say "ghost" because it simply isn't true, here in 2009. I say "haunt" because, six years ago, it was true—at least, partly.

The time: August 27, 2003. The scene: Earth and Mars. The event: Mars is coming into opposition—the time when Earth passes directly between Mars and the Sun, and consequently Mars is closest to us and at the opposite point in the sky from the Sun—hence "opposition." A routine encounter, one that happens about every 2.2 years. But what's different with this Mars opposition is the distance between Earth and Mars at closest approach: the two planets are closer together than they have been in a very long time: a bit less than 35 million miles.

This was a very big deal, you may recall. We remember it very well at Chabot: On one of the evenings that weekend, we had 2000 people who came up to see Mars through our telescopes…. A close opposition is the best time to see a planet, and this was closer than average for Mars by maybe 10 million miles. (It was at another very close opposition of Mars when Percival Lowell made his famous "Martian canals" observations and Martian civilization hypothesis, back in 1894.)

At the time of the 2003 opposition, there were a lot of reports—emails, websites, blogs—flying around describing the event, in some cases with exaggeration. One exaggeration is the amount of time since the previous closest encounter with Earth. Different accounts suggested a thousand years, ten thousand years, even one hundred thousand years. Technically this may have been true, if one were calculating down to the inch. Practically speaking, however, the opposition in 1924 was almost as close, by a difference of only 12,000 miles (one and a half Earth diameters).

The other (gross) exaggeration was a statement made that at opposition Mars would appear as large as the Full Moon. That would be spectacular! However, at some point a piece of information was lost from the original message: the part about needing to look at Mars through a telescope to achieve the advertised view.

The final piece of information missing from that message—which gave birth to the annual Mars Hoax –was the year, 2003, omitted along the way and making every August 27th a day to view the splendor of Mars in all its glory. But, alas, the ghost of Mars.

For the record, the next extra-close opposition of Mars will occur on August 15th, 2050, when it will be only 200,000 miles farther than the 2003 near-miss….




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Google Mars

June 5th, 2009 by Ben Burress

Google Mars view from the slopes of the Olympus Mons caldera. Credit: Google Earth

I was sitting at my computer the other day, quietly exploring minute details of the surface of planet Mars, when I realized once again that in my lifetime planetary exploration has gone from telescopic-view-only to robotic rovers poking microscopes close up at Martian geology!

Did I say quietly exploring the surface of Mars? Yes I did—and you can, too. First of all, if you're not familiar with Google Earth, please go and google Google Earth and get your free download today (this is NOT a sales pitch!). A modestly powered computer with a decent graphics card is all you need to probe every nook and cranny of planet Earth, sometimes to the detail of spotting people walking in the streets….

But there's a magic button on Google Earth (it looks like planet Saturn, for some reason) that instantly transports you to planet Mars—Google Mars, that is. It's a simple button click to explore Mars, Google Earth style.

This detailed digital Mars has been created with all of the data collected by the fleet of robots we've sent—from Viking to Mars Global Surveyor to Mars Odyssey to Mars Express to Mars Reconnaissance Orbiter (MRO), and of course Pathfinder, Phoenix, and the Mars Exploration Rovers, Spirit and Opportunity.

First on my itinerary was Olympus Mons, that extinct, Arizona-sized shield volcano that rises 15 miles above the average global terrain. Swooping into the San Francisco Bay-sized caldera, I got a sense of what it would be like to be there, standing on the caldera rim. There were even strips of super-high resolution imagery provided by MRO's HIRISE camera, allowing me to hover maybe a hundred feet above the ground and see rocks and piles of sand!

Next on the list had to be that other famous gargantuan feature, Valles Marineris, the "Grand Canyon of Mars" which, if it were moved to Earth, could stretch from Oakland, California to New York City—putting Grand Canyon National Park within a day's drive of anyone in the US…. Google Earth/Mars has a flight simulation mode that allows you to pilot an aircraft over and through (and into) the terrain.

Like a kid in a science supply shop (okay, that's the kind of kid I was), next I hopped on up to the landing site of NASA's Phoenix lander, on the wide flat plains near the Northern Polar Ice Cap. Yup, those plains are really flat. To my delight, I found that someone had inserted a panoramic picture taken by the orbiting MRO spacecraft when it captured Phoenix descending through the atmosphere.

Onward, planetary explorer…. I had to feel—not just see, but feel—what the landscapes that Spirit and Opportunity have been exploring for 5 years are like. On Spirit's side of the globe, Gusev Crater, I poked about the Columbia Hills, following in the tracks of the robot. Over at Opportunity's digs, I dropped into Victoria Crater, enveloping myself in "Street View"-style panoramas that almost set my feet down on Martian soil.

Okay, I could go on telling you about my adventures on Mars for days—but since you can do it yourself now, I'll let you go to it. Have fun, and send back a postcard! (Which, by the way, you can do from Google Mars….)




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Hubble Gets a New Lease on Space

May 22nd, 2009 by Ben Burress

The Hubble Space Telescope being serviced by Space Shuttle
Atlantis astronauts in May 2009. Credit: NASAFour hundred years ago, Galileo built his telescope and became the first on record to point the new device (invented the previous year) at objects in the sky. Today (in fact, even as I write!) what has become a symbol for the current state of evolution of the telescope—the Hubble Space Telescope–is being repaired and upgraded by the crew of the Space Shuttle Atlantis…for the last time.

Galileo's telescope had a magnification of only about 27x, allowing him to see that Venus has phases like the Moon, Jupiter has four large moons of its own, Saturn does not appear as a simple disk but has unusual "projections" to either side, and the Milky Way contains far more stars than is apparent to the naked eye. And though these are features that can be seen through the least powerful home telescopes today, Galileo's observations changed the way we look at the universe.

Hubble has done the same thing, but on a modern scale of magnitude. Not a large telescope by the standards of ground-based behemoths like Keck in Hawaii (Hubble's primary mirror is 2.4 meters in diameter), Hubble's "edge" is it's location in space, orbiting the Earth over 300 miles high, outside of our atmosphere. Particularly in its earlier days before ground based telescopes were using adaptive optics techniques to compensate for atmospheric distortion, Hubble's vision on the universe was unparalleled in its clarity.

Here's is a recap of a few of the many big discoveries Hubble has made possible:

Dark Energy: By accurately measuring the distance and velocity of distant supernovae, over a large range of distances, Hubble has refined out knowledge of the rate of expansion of the universe–leading to the discovery that the expansion of the universe is actually accelerating, contrary to what was expected. Scientists suggest the existence of a mysterious "dark energy" throughout the universe that exerts an antigravitational repulsive pressure on the cosmos.

Age of the Universe: Since Edwin Hubble (for whom the Space Telescope was named) discovered that the universe is expanding, astronomers have been trying to determine how long ago the expansion began–how long ago the "starting gun" of the Big Bang was fired, and thus the beginning of the universe. Through precise observations with the Hubble, astronomers in recent years have been able to peg it between 12 and 14 billion years. (Most recently, observations made with the WMAP mission have honed that down to 13.7 billion years, give or take 0.13 billion.)

Supermassive Blackholes: Hubble found the clues that point to the existence of "supermassive" blackholes at the heart of maybe most–or every–galaxy. The Milky Way's own central blackhole has a mass equivalent to four million Suns.

Stellar Dust Disks: Before the first extrasolar planets were actually detected, Hubble observations revealed that flat disks of dust encircling young and developing star systems–aka "protoplanetary disks"–is commonplace. This has given us a glimpse at what our own solar system may have looked like before the planets formed.

It has been seven years since the last Hubble servicing mission, with another servicing scheduled a few years ago cancelled in the wake of the Columbia disaster. Several failing systems will be repaired or replaced this time, and other instruments are receiving upgrades that will make Hubble more powerful than ever in its declining years.

This mission to service the Hubble will be the last. Since NASA is retiring the Space Shuttle fleet after 2010, we will no longer have a space vehicle large enough to carry upgrade and replacement equipment to and from the Hubble. After that, the next new big space-based descendent of Galileo's spyglass will be the James Webb. Stay tuned…




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Shooting the Moon

May 8th, 2009 by Ben Burress

Artwork from Jules Verne’s 1865 novel, From the Earth to the MoonLaunching a spacecraft bound for the Moon with the deliberate intention of striking the Moon in a spectacular impact!

Sounds like something out of a Jules Verne novel… but that's exactly what NASA's up to this year with the upcoming LCROSS (Lunar Crater Observation and Sensing Satellite) mission, scheduled for launch on June 2nd and impact sometime in October– exact date TBA.

And it's not unprecedented, either: the Lunar Prospector spacecraft back in 1998/1999, whose instruments detected possible signs of water ice in craters around the Moon's poles, was crashed into the Moon's South Pole at the end of its mission. The aim was to blast up a cloud of material from the lunar surface and spectroscopically analyze the plume in search of water vapor. None was detected then, but that's where LCROSS comes in.

LCROSS will seek to verify the presence or absence of water ice and related hydrated materials buried at the bottom of a permanently shadowed crater floor on the Moon's South Pole. Water ice cannot persist on any part of the Moon's surface that is subjected to sunlight, but because of the Moon's low axial tilt with respect to the ecliptic (the Sun's apparent annual path in the sky)– only about 1.5 degrees– there are craters at the Moon's poles whose floors never see the light of day, all month long and year round. Water ice could persist near the surface in these places.

LCROSS consists of two pieces: a "Shepherding Spacecraft" that will guide the whole affair to the proper location on the Moon's South Pole, and the Centaur rocket stage that propelled the spacecraft to the Moon. The pair will separate, and the Centaur rocket will become the primary impactor, striking ground and producing a crater and plume of ejected material. Viewing the event from above, the Shepherding Spacecraft will use cameras and other instruments to analyze the plume from a distance, and will then follow the same course as the Centaur, descending four minutes after impact through the ejected plume and analyzing material samples as it falls.

Then, the Shepherding Spacecraft, too, will impact the Moon– and the plume it kicks up may well be visible through modest sized telescopes on Earth. We're planning to watch the explosion live through our telescopes at Chabot, weather permitting. Keep an eye on our website for details.

Now, back to Jules Verne for a moment. The launching of a projectile with the intent of striking the Moon was indeed the subject of one of his novels, From the Earth to the Moon, published in 1865. Fired from an enormous cannon, the goal of that post Civil War mission was to catch the attention of anyone living on the Moon, to open up a line of communication with their civilization.

My wife asked me if crashing a probe into the Moon would have any harmful effects, particularly if in fact there is any form of life (subsurface microbes or such) living there. Well, certainly, if you happen to be a lifeform living at ground zero of the impact… but the fact is the Moon is frequently struck by meteorites much larger than the LCROSS impactor anyway. To paraphrase Douglas Adams, "that kind of thing goes on all the time."

One last fun tidbit about the Jules Verne novel: the launch site for his cannon-fired projectile was a place in Florida, 50 miles south of Tampa Bay, and only about 135 miles from the Kennedy Space Center, from which LCROSS will be launched…




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Springtime on Mars

April 24th, 2009 by Ben Burress

NASA/Mars Reconnaissance Orbiter; Fans of dark dust on Mars'
southern ice cap, apparently blasted from beneath the ice
by thawing carbon dioxide."

It's spring again, that time of year when my thoughts return to…blasts of carbon dioxide gas jetting up from beneath the frigid layer of dry ice below, carrying rusty red dust in plumes that jet toward the pale skies….

At least, that's what happens at the polar ice cap on the planet Mars. I'd sure love to be there to see it, even if there are no flowers in bloom. Still, there seems to be plenty of "blossoming" going on….

NASA's Mars Reconnaissance Orbiter—the spacecraft with that high powered camera that could spot a beach ball on Mars' surface—has captured images of the aftermath of some of Mars' springtime polar action. Appearing as dark fan-shaped bursts strewn across the thinning springtime polar ice, these features are explained as plumes of Martian dust that have settled after being blasted into the air by releases of gas pressure from under the surface of the ice.

To describe what's going on, let me paint a picture of the Martian polar region as it emerges from the deep freeze of winter into spring.

Mars' year is almost twice as long as Earth's—and so too are its seasons. Winter at the southern pole of Mars lasts almost six months. In that time, the normally freezing temperatures on the Red Planet plummet to as low as -225 degrees Fahrenheit at the pole. During this time, Mars' permanent water ice cap acquires a layer of frozen carbon dioxide (dry ice) on top, formed from carbon dioxide freezing directly out of the atmosphere.

This seasonal dry ice cap also forms around the edges of the water ice cap, covering adjacent ice-free surfaces as well. The carbon dioxide ice cap may grow to as much as a meter thick.

Then, as spring approaches and the ice cap gradually comes out of the dark and receives more and more sunlight, it begins to warm up (though don't get the impression that it is ever "warm" anywhere on Mars' surface! Air temperatures recorded by the Viking landers in Mars' more temperate latitudes was barely ever higher than 1 degree Fahrenheit). Spring Equinox in Mars' southern hemisphere was on December 26th.

As the layer of solid carbon dioxide heats up, its ices turn to gas, both at the top of the layer and beneath it as well. The gases forming underneath build up pressure, which seeks a path to escape. Evidently the pressurized carbon dioxide gas can actually carve channels in the Martian soils under the ice as it flows—said channels have been seen in the past after the seasonal ice cap dissipates entirely.

When the gases find a weak point in the ice, they can erupt upward, bursting into the air, sometimes carrying dust with it. The dust rockets skyward and is blown by prevailing winds, settling out on the ice in great dark fans—which is what Mars Reconnaissance Orbiter has shown us.

Ah, to be on Mars in springtime….




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Is the Sun Pulling a Rip Van Winkle?

April 10th, 2009 by Ben Burress

Our Sun has a well-observed cycle of rising and falling magnetic activity that runs its course about every 11 years. But as cycles in nature teach us time and time again, you usually can’t set your watch or your calendar by them.

The Sun seems to be unusually quiet these last few years– and solar scientists are excited by this long, deep slumber of activity because it is the first of its kind that has occurred since modern (space-based) solar observation began back in the 1960s.

The Sun is a huge ball of hot, electrically charged gas (plasma– mostly hydrogen and helium ions and electrons). Its constant internal motions of plasma– the rising and falling of convection cells, the non-uniform rotation of the Sun that involves a lot of twisting and sheering– generate magnetic fields, as any kid who has built an electromagnet might guess. In an electromagnetic, an electric current (moving electrons) generates the magnetic field.

The Sun’s magnetic fields can grow quite strong in areas, generated beneath the Sun’s visible surface (photosphere) and rising up through that surface and into the Sun’s enveloping atmosphere. At the photosphere, the magnetic fields tend to suppress the rising convection of plasma, choking the flow of heat from the interior to the surface and making spots that are less hot than the general surface (4000 degrees as opposed to 6000 degrees). The cooler spots are less bright, and we call them sunspots.

The same magnetic fields that leave their mark on the photosphere as sunspots rise into the solar atmosphere, where their sometimes violent twisting and interaction heats the gases there, and can power violent explosions such as solar flares and coronal mass ejections, both of which can affect the Earth.
So, sunspots are a visible sign of magnetic activity, and over the last 400 years of regular observations and counts of sunspots, a distinct 11-year cycle from one peak of activity to the next has been identified. Between peaks of activity (called solar maxima) are periods of relative "quiet," magnetically speaking, when there are few if any sunspots observed, and events like solar flares and such are not common.

We are currently in the midst of a solar minimum– the last solar maximum that occurred was around 2000/2001. But what has scientists buzzing right now is just how "deep" a sleep the Sun seems to be in. 2008 was the quietest year for the Sun on record since the beginning of the space age. Out of the 366 days last year, on 266 of them the Sun was completely spotless, which is well below "normal" for a solar minimum year.

What does it mean? Well– that’s difficult to say right now. Scientists are still trying to understand why the Sun experiences its 11–year cycle at all. And it’s not unprecedented; the Sun has experienced "deep minima" before. In 1913 there were 311 spotless days. Other deep minima have been seen in the sunspot record, and in almost every case normal solar activity returned; the next solar maximum is expected to peak in 2011 or 2012– perhaps 2013.

There is no indication that the Sun will remain quite and mostly spot free for an extended period– such as it did in the 17th Century, when the Sun remained quite for about 70 years!




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Asteroid Apophis–Hit or Miss?

March 25th, 2009 by Ben Burress

Apophis is about the same size as the asteroid that blasted
the mile-wide Barringer Crater in Arizona.
Credit: David Roddy, USGSFriday the 13th, April, 2029: If you're superstitious, this might not be a good day to schedule a near-Earth asteroid encounter. But, as it happens, that's the day that the Near Earth Asteroid (NEA) Apophis will make a very close flyby of Earth–a once in 800 years event for an asteroid Apophis' size.

Fortunately, scientists have already predicted, 20 years in advance, that this is our lucky day: Apophis won't hit the Earth at that time. Rest assured (pretty much).

Discovered in 2004, Apophis is an asteroid about 270 meters across that orbits the Sun at distances ranging from about one astronomical unit (1 AU; the distance between Earth and the Sun) and about three quarters of an AU. Apophis orbits the Sun once every 323 days.

After its initial discovery, before our knowledge of its orbital trajectory had been refined, astronomers had predicted that there was a small chance it could hit the Earth on April 13, 2029, but as we got a clearer picture of its orbit the probability dwindled to practically nothing. Instead, Apophis will pass by Earth no closer than about 18,000 miles. Whew! Disaster averted, and we didn't even have to send Bruce Willis to deal with it.

But wait–that's not all. Though Apophis almost certainly won't hit us in 2029, there's a chance that this close encounter will set the asteroid up for an impact with Earth in 2036–something like 1 in 45,000.

So, if we know there won't be an impact in 2029, why don't we know whether or not there will be one in 2036? Why all the suspense?

Here's where I pull out my pinball analogy. Think of a pinball machine. The play zone around your flippers represents near-Earth space, the various bumpers up in the field represent all the planets, the Sun, and other large asteroids of the Solar System, and the pinball represents a Near Earth Asteroid, like Apophis.

When the pinball inevitably comes into the play zone, there are two possibilities: either it will hit (or be hit by) one of your flippers and thus be deflected back into the field where it will bounce around some more between bumpers, or it will sail right through that dreaded "window" between the tips of the flippers and fall into the end pocket–which represents Terra Firma and a catastrophe if a NEA falls there. As any pinball player knows, it's nearly impossible to predict exactly what path the pinball will follow into the play zone until it gets close.

It's a lot like that with a NEA in the Solar System: as it orbits around the Sun, its course is influenced by the gravitational pull of planets, large asteroids, and potentially smaller asteroids that it might pass close to. A very small deviation in a NEA's direction or speed can, over time, "amplify" into a very large difference in position much farther down the road.

Given the 2029 close encounter with Earth, though we're reasonably confident Apophis won't hit us on that pass, we don't know precisely how that encounter will alter Apophis' orbit. The gravitational interaction between Earth and a NEA passing close by is a complex one, with many variables, not the least of which is Earth's non-uniform gravitational field.

If Apophis passes Earth through precisely the right "window" in 2029–say, right between the flipper tips–then it could be set up for an impact at its 2036 encounter. That window, called a gravitational keyhole, is only about 600 meters across for the 2029 encounter.

As we gather more data on Apophis, we'll get a better prediction for what may happen in 2036–but right now the odds are that it will ultimately miss us at that time. That's a good thing, too, because at that time Bruce Willis will be 81 years old… and even John Glenn was only 80 when he returned to space…




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First Star I See… In My Life!

March 13th, 2009 by Ben Burress

Tycho Brahe observing the 1572 supernova, with astonished
spectators.
What's that up in the sky? A… uh… an… uh…. Golly, never seen that before…

Ever seen one of those? I won't say UFO, because that immediately conjures images of flying saucers and big-eyed space aliens, and that's not what I’m going for here. What I mean is, have you ever seen something in the night sky that you have "never seen before," but that you later learned was actually a natural and recurring apparition, like the appearance of Venus as the Evening Star?

This time of year usually stirs up a phone call or email or two involving "first time" sightings of the bright star Sirius, whose brilliant, multi-colored twinkling catches some people's attention at least once in their lives, causing them to gawk and either wonder why they'd never noticed it before, or assume it's a new thing in the sky, some rare and unusual occurrence.

Sirius did the same thing to me when I was in Junior High. I walked outside one night, looked up, and saw this glittering spectral jewel, brighter than I could remember any star I'd seen. This hook, or teaser, inevitably led me into the adventure of star gazing, because I had to find out what that thing was. But this kind of "revelation" can happen to people much later in life– and in hind sight I'm amazed I hadn't noticed it when I was even younger.

For the past few months, Venus has been in the western sky as the Evening Star– so naturally I’ve been getting more calls than usual. A man who I would guess (by his voice) was past middle age called to report the brilliant white light in the western evening sky, and was stunned to find out it was Venus. I could hear the amazement in his voice that he had never before noticed Venus in his life, after I told him that Venus comes and goes, alternately from the evening and morning skies, but comes back regularly.

And finally I've reached the "point" of this blog: how we can go through sometimes decades of our lives without noticing, or fully registering, something of unusual beauty that has more or less been "in plain sight" all along (or periodically, at least).

My feeling is that is must have a little to do with timing, a little to do with prevailing conditions in our lives, and a lot to do with how we focus our attention on the world around us, or above us. One day we might look to the evening sky and see brilliant Venus flashing over the horizon and not see anything unusual; twenty years later we might look at essentially the same scene and all of our attention and wonder is suddenly drawn to that inexplicably bright light.

See what you think. Go outside one evening in March, look to the south and see if you can spot Sirius– it'll be to the left of Orion's Belt, if you can find that. And, if you're reading this anytime before, say, March 20th, look to the west after sunset and look for Venus. Maybe you've seen these objects before, and know exactly what I'm talking about. Or, maybe, you'll experience something for the first time in your life. Worth a try, isn't it?




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NASA's Kepler: Staring Down Earth-like Planets

February 27th, 2009 by Ben Burress

For several years there has been a lot of buzz about the detection of extra-solar planets, or exoplanets: planets orbiting stars other than our Sun. However, due to the limits in technology and observational capabilities, to date only large, gas giant planets orbiting close to the stars (so called "Hot Jupiters") have been found, with a possible exception or two.

The main method for detecting exoplanets is by spectroscopically observing a tiny "wobble" in a star caused by the gravitational tug of a massive planet in orbit. Only Jupiter-sized planets have enough pull to produce a wobble in their star that we can detect—and the closer they are to their star, the shorter their orbital period and the more wobbles we can measure in a given period of time. The gravity of an Earth-sized planet is too feeble for this and planets at Earth-like distance orbit only once in many months.

But NASA is about to launch a new spacecraft, Kepler, whose mission is to detect Earth-sized planets at Earth-like distances from their stars. Kepler will launch on March 5th, and will eventually move into an orbit around the Sun. In essence, Kepler is a giant space camera designed to "stare" at a chosen patch of the sky continuously for years to come.

So what exactly is Kepler looking for in its unblinking stare contest with the stars in its vision? Kepler won’t be looking for microwobbles in those stars. Kepler will detect planets through the transit method. A transit is when a planet crosses in front of its star, blocking off a tiny amount of the star's light for a time.

A number of the hot Jupiters have been detected by their transits across their stars: a large planet can block a measurable amount of their star's light. But the drop in a star's brightness caused by an Earth-sized planet is far smaller—and if that planet only orbits its star every year or so, with its infrequent transit lasting only a few hours, an observer would have to stare long and hard to notice it.

Kepler will be based in space, and will be able to observe its target patch of sky continuously, uninterrupted by the cycles of day and night on Earth. Also by virtue of being in space, Kepler won't be hampered by Earth's turbulent and obscuring atmosphere—so there will be far less "noise" in the starlight, noise that can hide a minute drop in brightness. Finally, Kepler's sensitive digital camera system is an array of 42 CCD chips positioned at the focus of a 0.95 meter telescope, which will image an area of the sky about 12 degrees in diameter—equivalent to the area of sky you can cover with your open hand at arm's length.

Kepler will stare at a patch of sky near the constellation Cygnus, constantly monitoring about 150,000 stars for the next few years, looking for minute drops in brightness that may be the passage of Earth-sized planets.

Kepler won't reveal the composition or atmospheres of Earth-sized planets, or any telltale signs of life. Perhaps more importantly at this stage of our exploration of space, Kepler should give us an idea of how numerous Earth-sized planets are out there—whether or not they are as commonplace as depicted on Star Trek…

Good luck, Kepler, and stare on!




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