Slideshow: Stamps look down on our planet

Click through imagery of our planet as seen from above in the U.S. Postal Service's "Earthscapes" stamp set.

Launch slideshow

The only problem with putting out a set of stamps that celebrate America's landscapes, as seen from above, is that the postage-stamp size hardly does justice to the aerial vistas. That's why we're giving you the "Earthscapes" imagery in slideshow form.

The 15-stamp set, which features pictures from aerial photographers and Earth-orbiting satellites, is available starting today from the U.S. Postal Service. The "Forever" stamps had their official unveiling at NASA's Goddard Space Flight Center in Maryland.

"Once you've seen the world from above, you never look at it quite the same way again," Joseph Corbett, the Postal Service's chief financial officer and executive vice president, was quoted as saying in a NASA news release about the kickoff. "That's why the Postal Service is proud to offer these Earthscapes stamps, which invite us to take a bird's-eye view of the land we all share."

Two of the images are from the Landsat 7 satellite, and one comes from GeoEye's Ikonos satellite. The other 12 were taken by aerial photographers. One photographer, 81-year-old Jim Wark, took five of the photos, showing Utah's Castle Butte, a railroad roundhouse in Pennsylvania, a barge operation in Houston, a skyscraper in Manhattan and a geothermal spring in Yellowstone.

Wark spends hours in his plane looking for great shots. "I'm looking for the pictures that the other guy doesn't have," Shutterbug magazine quoted Wark as saying.

The Landsat images serve as a fitting way to celebrate the 40th anniversary of the first Landsat launch. "NASA has been at the forefront of looking at Earth from the unique vantage point in space," Chris Scolese, director of Goddard Space Flight Center, said at today's ceremony. In case you're not content with just 15 pictures, here are more long-range views of Earth worth clicking through:

• Slideshow: Earth as art
• More 'Earth as art' from Landsat
• See the world from the space station
• Peace over Earth: 2011 holiday calendar

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

The five-day window for the launch of a North Korean rocket mounted with an observation satellite opened Thursday as the rest of the world waits to see if Pyongyang will defy international warnings and go ahead with the controversial mission.

NBC News is in North Korea to observe the launch with space expert James Oberg. With a 22-year career as a space engineer in support of NASA’s spaceflight operations, Oberg has the experience and technical expertise to determine the veracity of North Korea’s claims about this mission.

Oberg answered reader questions for an hour earlier today. The questions and answers were extremely engaging and informative.
Click below to replay the chat.

Read some of Oberg's reports on North Korea's space program:

What happens if North Korea's satellite fails?

North Koreans desperate for Western approval of launch

North Korea's 'unconvincing' answers to satellite questions

NBC space expert on North Korea satellite launch: 'It's not a military missile...but it's darn close'

DigitalGlobe

This picture from DigitalGlobe's QuickBird satellite shows the launch pad at the Tongchang-ri Launch Facility in North Korea, as seen on April 9. Three dark-colored support vehicles are lined up on the launch apron. The rail-mounted mobile launch platform is toward the bottom of the pad, with an exhaust deflector that's designed to deal with the hot blast of launch.

While North Korean officials were showing off their preparations for a controversial satellite launch, DigitalGlobe's Quickbird satellite was snapping high-resolution pictures of the scene from far above. The images reveal how far the North Koreans have come — and how much can be gleaned about their intentions from orbit.

DigitalGlobe is a commercial satellite imagery provider, and QuickBird can provide pictures at a resolution of a half-meter (20 inches) per pixel. But you can bet that U.S. intelligence agencies are getting significantly better views of the Tongchang-ri Launch Center from their satellites.

North Korea is due to launch its Unha-3 ("Milky Way 3") rocket anytime between now and April 16, ostensibly to send an Earth-observing satellite known as Kwangmyongsong-3 ("Bright Shining Star 3") into a pole-to-pole orbit. The United States and its allies worry that the launch is really more of a test of North Korea's capability to launch intercontinental missiles as weapons.

International journalists, including a team from NBC News, were invited to visit the secretive hard-line communist nation this week for an on-the-ground assessment of the space mission. NBC News space analyst James Oberg said that in its current configuration, the booster is "not a military missile ... but it's darn close."

"This rocket is not a weapon, but it's maybe 98 percent of one," Oberg said. "It can be converted all too easily and all too frighteningly into a weapon, and they don't need it."

AmericaSpace's Craig Covault said the Tongchang-ri facility is clearly built to handle rockets much larger than the Unha-3. He quoted U.S. and South Korean intelligence analysts as saying they believe the complex could be used for tests of North Korea's "Satan" long-range ballistic missile, as well as a North Korean-Iranian booster with up to six engines clustered in the first stage.

"Iran and possibly North Korea plan to use the large new space launch booster to send Iranian and North Korean astronauts into space," Covault wrote. He lays out a Korean-Iranian missile development program that sounds positively scary.

North Korea might have been hoping that this week's visit by journalists would put Washington's fears to rest. But based on the feedback so far, it doesn't sound as if that'll be the case.

Here's tonight's report from NBC News' Richard Engel in Pyongyang:

... Here's a computer-generated animation of the expected launch from Analytical Graphics Inc.:

... And here are more satellite pictures from DigitalGlobe:

An orbital view from DigitalGlobe's QuickBird satellite shows North Korea's Tongchang-ri Launch Facility from an altitude of 420 miles (680 kilometers).

James Oberg / msnbc.com (left) / DigitalGlobe (right)

The map of the Tongchang-ri Launch Facility that was displayed by the North Koreans during a news briefing (left) is compared with the overhead view from DigitalGlobe (right). The orientation of the satellite picture has been rotated to approximate the orientation of the map.

DigitalGlobe

This satellite view shows the horizontal processing building at the Tongchang-ri Launch Facility in North Korea, with a support vehicle parked in the dark-colored parking lot below the building.

DigitalGlobe

This DigitalGlobe satellite image, taken from orbit on April 9, shows the Tongchang-ri Launch Facility in North Korea. The structure in the lower part of the frame is known as the high-bay processing building, and the structures in the upper pat are housing facilities. VIP housing is at leff.

More about North Korea's space plans:

• North Korea says it's fueling rocket for launch
• What you need to know about the launch
• North Koreans desperate for Western approval
• Clues about North Korea's plans come to light
• North Korea shows off its launch pad and satellite
• Q&A: Rocket is 'not a military missile ... but it's darn close'
• World News: NBC gets a rare peek inside North Korea
• PhotoBlog: Pictures from the North Korea rocket tour
• Inside North Korea: Closely watched launch poses risks
• North Korea's launch sparks more worries than Iran's
• A look at North Korea's rocket technology

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

When and where will Russia's doomed probe to a Martian moon fall back to Earth? The RIA-Novosti news service caused a stir when it reported that the 13-ton Phobos-Grunt spacecraft would crash in southwestern Afghanistan at 2:22 a.m. Moscow time on Jan. 14. The report attributed the prediction to the U.S. Strategic Command, but experts say it's way too early to be that precise about the Phobos-Grunt debris zone.

"Yes, it is much too early to predict" the circumstances of Phobos-Grunt's re-entry, Gene Stansbery of NASA's Orbital Debris Program Office at Johnson Space Center told me today.

The U.S. Strategic Command is being circumspect as well, deferring comment to NASA and to Roscosmos, Russia's space agency.

The most that can be said about the impact zone right now is that it will be somewhere between 51.4 degrees north and 51.4 degrees south latitude. That's a swath of the planet that stretches from Calgary, Alberta (or Ghent, Belgium) in the north to the Falkland Islands in the south and takes in the vast majority of the world's population. Satellite-watcher Marco Langbroek reports on the See-Sat-L discussion forum that the predicted time of re-entry is Jan. 13, plus or minus 11 days. A couple of weeks ago, Roscosmos estimated that re-entry would come sometime between Jan. 6 and 19.

Typically, the projected area of the debris zone can't be narrowed down until hours before re-entry, if then. It's possible that RIA-Novosti picked up on a prediction that was centered around a precise time and place of re-entry, but left out the part about the plus-or-minus uncertainty. (You can see where Phobos-Grunt is right now by checking the Heavens-Above website.)

The spacecraft was launched from Russia's Baikonur Cosmodrome in Kazakhstan on Nov. 9 local time, and was supposed to leave Earth orbit hours later for the trip to Phobos, the larger of Mars' two moons. Along the way, it would have deployed a Chinese mini-probe in Martian orbit. If everything went well, the $165 million Phobos-Grunt mission would have brought a sample of Phobos soil back to Earth in 2014. ("Phobos-Grunt," or the more correctly transliterated "Fobos-Grunt," is Russian for "Phobos-Soil.")

Everything didn't go well, as we now know: The spacecraft's upper-stage thrusters didn't fire, and it's been stuck in Earth orbit ever since. This month, Russian officials finally gave up on attempts to revive the craft and admitted that it would fall to its destruction next month.

Most of the spacecraft's mass consists of the toxic propellants it would have used to get to Phobos. There's also a small amount of radioactive cobalt-57 that was meant to power a spectrometer. The Russians say that the fuel will burn up in Earth's atmosphere, and that the cobalt won't pose a contamination threat.

Twenty to 30 parts from the probe with a total weight of up to 440 pounds (200 kilograms) are expected to survive the plunge. One of those parts could be the sample return capsule, which is designed to withstand the intense heat of atmospheric re-entry. David Warmflash, the principal investigator for one of the mission's experiments, said "it is quite possible" that his team's LIFE capsule will make it back to Earth intact.  

If it lands in Afghanistan, the chances of recovery might be poor, given the proximity to a war zone. But if it lands in the ocean, which is currently the likeliest scenario, the chances aren't any better. Over the past few months, two other high-profile satellites — NASA's Upper Atmosphere Research Satellite and Germany's ROSAT space telescope — fell through the atmosphere over the South Pacific and the Bay of Bengal, respectively, and no trace of them was ever found.

More about Phobos-Grunt and other falls to Earth:

• Mars probe to crash to Earth in January
• Russian leader suggests punishing space failures
• Skywatcher snaps photos of stranded probe
• Christmas Eve fireball sparked by Russian rocket debris
• Russian communications satellite falls after launch

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

AGI

A map from Analytical Graphics Inc. shows the ground track for NASA's UARS satellite for the 28 hours from 2 a.m. ET Friday to 6 a.m. ET Saturday — which reflects The Aerospace Corp.'s estimate for the time of re-entry. During that time frame, the satellite will follow the narrow blue tracks shown on the map, but will not fly above the areas shown between the tracks.

Updated 6 p.m. ET Sept. 23:

Now that experts are narrowing down their forecasts for the fall of the six-ton Upper Atmosphere Research Satellite, you can easily work out when to look for it streaking through the sky.

Here's the step-by-step process:

1. Go to the Heavens-Above website.
2. Select your "current observing site" ... the easiest way to do that is to click on the "from database" link, select your country ("U" for the United States), then enter a search string for a city name (say, "Dubuque," which is where I'll be on Friday). You can also use a map, or enter in your latitude and longitude manually.
3. Submit your choice for observing site. That will bring you back to the home page, with your latitude/longitude listed.
4. Click on the link for "All Passes of UARS."
5. Check out the chart that comes up, and make sure the correct time zone is listed. This chart lists all the times when UARS is within the line of sight from your location. Sometimes the satellite may passing by, but you can't see it because it's lost in the daylight, or it's not reflecting any sunglint. At other times, the satellite catches the glint of the sun just right to become visible in the sky. You can get a list of those sighting opportunities by clicking the "Visible Only" button instead of the "All" button.

Heavens-Above

This chart shows UARS' sighting opportunities between now and Friday from Dubuque, Iowa.

This shows you when the UARS satellite is passing through between now and the end. But if you want to find out when there's any chance of seeing the UARS satellite fall, you have to focus on the passes that occur on Sept. 23 or early Sept. 24. For Dubuquers, there was an opportunity at 4:36 a.m. CT Sept. 24, as listed on the chart. The satellite wouldn't have been visible at that time — unless flaming pieces of debris were falling to the ground.

In that theoretical scenario, I would be watching for something streaking from west-northwest toward the south. But I wouldn't be looking very high in the sky. Heavens-Above is telling me that the maximum height above the horizon would be about 22 degrees. Ten degrees is roughly equivalent to the width of your fist held out at arm's length, so I'd look a little more than two fist-widths high.

The chart also tells me that debris from the satellite wouldn't have hit anywhere close to me, even if it was falling at the time, because the flyover is too far away. The "Alt" (altitude) listing is the key. "If your location has a pass with elevation above 80 degrees — that is, nearly overhead — then yes, you are in the potential debris scatter field," NBC News space analyst James Oberg said in an email explaining the process.

Fireworks on tap
What could observers see? Space.com's skywatching columnist, Joe Rao, said the blazing re-entry would look like a "short-lived but spectacular fireworks display." At an altitude of about 50 miles (80 kilometers), chunks of the burning satelllite would break off and create a series of meteoric streaks. Large pieces would flare into fireballs that could blaze as brightly as the full moon, if the re-entry occurred at night, Rao said.

AGI

An illustration by Analytical Graphics Inc. shows the UARS satellite breaking up in the upper atmosphere.

It's far from certain that such a sight would be visible from the United States, based on NASA's estimates. The space agency said there was just a "low probability" that the satellite would be crossing North America when it made its final plunge, sometime late Friday or early Saturday.

Other experts are offering different forecasts that have been all over the map ... literally.

The Aerospace Corp.'s prediction is being updated more frequently than NASA's. At one time, it pinpointed UARS' re-entry in the south Pacific, and then the crosshairs shifted to Chad in central Africa, and then back to the Pacific. All these predictions have a wide margin of error. NASA estimates that there'll be a 6,000-mile (10,000-kilometer) margin of error even two hours in advance of the fall.

Satellite-watchers are really hoping the debris from UARS falls somewhere near them, so they can witness a spectacular sky show (and maybe even catch it on video). But others are worried about the risk of injury or damage.

Reviewing the risk
The UARS satellite is the largest unmanned NASA spacecraft to make an uncontrolled descent since 1979, when the 10.5-ton Pegasus 2 satellite and NASA's 77-ton Skylab space station fell to Earth. (Other notable re-entries since then include the controlled deorbiting of Russia's 138-ton Mir space station in 2001, the controlled re-entry of the 17-ton Compton Gamma Ray Observatory in 2000 and the tragic loss of the shuttle Columbia and its crew in 2003.)

NASA says the chances that anyone in particular will be hurt by UARS debris are incredibly small: A couple of weeks ago, Nicholas Johnson, head of the space agency's Orbital Debris Program Office, estimated that there's a 1-in-3,200 chance of anyone being struck by fragments. When you divide that risk among the nearly 7 billion people in a potential debris zone that stretches in latitude from northern Canada to the southern tip of South America, the risk to any particular person comes to less than 1 in 20 trillion.

NASA doesn't intend to update those odds as more becomes known about UARS' path. Those are merely the generic risk statistics for the re-entry of any space debris as big as the six-ton satellite. Johnson said one object that big comes down through the atmosphere roughly once a year. "The odds don't change," he said.

Thousands of space objects streak through the atmosphere every year: Just last week, for example, a fireball sighted over the southwestern U.S. caused a huge stir. But Oberg said the case of UARS is special because we know in advance that a fiery fall is coming.

"Unlike most rocks from space that fall on our heads, this falling satellite is known in advance, and it is that lengthy anticipation, not the inherent hazard, that makes it so newsworthy," he said. "Bigger rocks fall to Earth much faster and every day  — all naturally, but out of sight, out of mind."

More about the satellite saga:

• NASA: Satellite won't pass over America when it falls
• Watch the doomed satellite tumble in space
• What's the precedent for NASA's falling satellite?

Check NASA's UARS status page for updated information about the satellite's whereabouts, all the way to the end.

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding me to your Google+ circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

Update for 4:30 p.m. ET Sept. 23: NASA revised its forecast since this report was first posted to note that the Upper Atmospheric Research Satellite was not sinking as quickly as expected, and that there was a "low probability" that debris from the re-entry could fall on North America. The revised forecast said the satellite could come down late Friday or early Saturday, Eastern Daylight Time.

Earlier report from Wednesday: NASA says its derelict Upper Atmosphere Research Satellite is expected to make its final fiery plunge sometime on Friday afternoon ET and notes that "the satellite will not be passing over North America during that time period."

This afternoon's update suggests that Americans are not at any risk for injuries or property damage due to satellite debris. It also means they'll miss out on the fireworks.

For two weeks, experts on orbital debris have been telling people that the 20-year-old, bus-sized spacecraft would soon fall through the atmosphere and drop about two dozen pieces of debris on Earth — but until today, there was too much uncertainty to say exactly which day that would happen. In the morning update, NASA narrowed the time frame down to Friday. The forecast was refined further at 6:35 p.m. ET. But NASA said it couldn't yet be any more precise than to say it'll be Friday afternoon, Eastern Daylight Time.

"It is still too early to predict the time and location of re-entry with any more certainty, but predictions will become more refined in the next 24 to 48 hours," NASA said.

The six-ton satellite's orbit is limited to between 57 degrees north latitude and 57 degrees south, spanning the width of the world between northern Canada and the tip of South America. In the past, Nicholas Johnson, the head of NASA's Orbital Debris Program Office, has estimated that the chances that any of the UARS debris would hit anybody were 1 in 3,200 — which translates into a 1-in-20 trillion risk for any particular person.

NASA's Johnson told me today that he won't be recalculating the odds as the prediction becomes more precise. "At that point, we don't compute odds," he said.

NASA and its partners at the U.S. Strategic Command will be issuing updates on the timing at 24 hours before the expected fall, then at T-minus-12 hours, T-minus-6 hours and T-minus-2 hours — and we'll be passing those predictions along. But even two hours before re-entry, experts won't be able to project exactly where the debris will end up.

When UARS' predicament first came to light a couple of weeks ago, Johnson said the margin of error for the 500-mile (800-kilometer) fall zone would be somewhere around 6,000 miles, or a quarter of the way around the planet. The uncertainty arises because of a couple of factors: Solar outbursts, like the ones we've been getting over the past few weeks, lead to a faster decay of orbits for low-flying spacecraft. Also, the satellite is tumbling, which leads to unpredictable atmospheric-drag effects. Because there's no fuel left for orbital maneuvering, no one has any control over UARS' orbital course.

Most of the satellite will burn up in the atmosphere, but NASA estimates that about a half-ton's worth of fragments will survive re-entry and fall to Earth. The computer models suggest that the biggest chunk would weigh about 300 pounds (150 kilograms), or as much as a refrigerator. Anyone who happened to be in the vicinity of the debris fall would see bright streaks in the sky, much like the fireworks seen when pieces of Russia's Mir space station fell to Earth in 2001. 

The most likely outcome is that the remnants of the UARS satellite would fall into a desolate patch of ocean or an uninhabited stretch of land, far away from any witnesses or potential victims. "Throughout the entire 54 years of the Space Age, there has been no confirmed report of anybody in the world being injured or severely impacted by any re-entering debris," Johnson noted two weeks ago.

UARS was deployed from the shuttle Discovery in 1991, beginning a $750 million mission to study the upper atmosphere and its interaction with the solar wind. In 2005, it was shut down and placed into a disposal orbit, and its altitude has been slowly decaying ever since. Now the descent is picking up speed: NASA said its altitude at 1:30 p.m. ET today ranged from roughly 120 to 130 miles (190 to 205 kilometers).

Nowadays, satellite operators lay out a well-defined procedure for the safe disposal of Earth-orbiting satellites at the end of their lifetimes. In fact, NASA and its international partners are already devoting attention to what needs to be done when it comes time to get rid of the International Space Station, sometime after 2020. But back in the 1990s, when the UARS mission was launched, such issues were "really not given a lot of thought," Johnson said.

Update for 9 p.m. ET: If North America is out of the picture, what about the rest of the world? Take a look at the graphic on this webpage from The Aerospace Corp. to see why NASA has ruled out North America based on its time estimate.

The circled icon on the map indicates the position of the UARS satellite at 4 p.m. ET Friday. The blue curves show its orbital track before 4 p.m., and the yellow curves show the track after 4. If UARS re-enters the atmosphere before 4, the potential fall zones include the Atlantic, Africa, Middle East, north Asia and the Pacific. If it happens after 4, South and Central America, south Asia and Australia come into the mix. But it'd be well into Friday evening by the time the orbital track goes over the U.S. and Canadian East Coast. 

More about the satellite saga:

• Watch the doomed satellite tumble in space
• FEMA ready if plunging satellite hits U.S.
• Who'll get hit by a falling satellite?
• Real-time UARS tracking from N2YO.com 

Check NASA's UARS status page for updated information about the satellite's whereabouts, all the way to the end.

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding me to your Google+ circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.