With the Space Shuttle Endeavour scheduled to undock from the International Space Station (ISS) on Friday evening, skywatchers across much of the United States and southern Canada are in for a real treat early on Saturday and Sunday morning.

Weather permitting on these mornings, there will be opportunities to see both the Endeavour orbiter and the ISS flying across the sky from many locations.

Appearing as a pair of very bright "stars," the ISS should appear as a somewhat brighter object and will be trailing Endeavour as they move across the sky. The pair will appear only a few degrees apart on Saturday morning, but the gap between the two will likely widen to perhaps 20-degrees or more by Sunday morning (your clenched fist held at arm's length measures roughly 10-degrees; so on Sunday morning expect Endeavour and the ISS to separated by about two fist-lengths).

The sight should easily be visible to anyone, even from brightly lit cities. Considering that after this mission there will be only be four left before the shuttle program ends (tentatively in September) the view of a shuttle orbiter and the Space Station flying in tandem will soon be a sight that will pass into history.

New York's View

The Tri-State Area will get two opportunities to see Endeavour flying with the ISS. The first will come on Saturday morning, just over 9 and a half hours after both vehicles have undocked; so they will still be relatively close to each other. The two spacecraft will emerge from out of the Earth's shadow at 5:21 a.m. EST, at an altitude of 18-degrees above the north-northwest horizon. They will attain a maximum altitude of 25-degrees above the north-northeast horizon at 5:23 a.m. and will drop toward the eastern horizon at 5:25 a.m. If you're familiar with the constellations, you'll see them glide between Cepheus and the "W" of Cassiopeia and pass under the bright star Deneb in Cygnus. Overall, this pass should last about 3 minutes and 50 seconds.

Your other opportunity will come early on Sunday. By then, the two spacecraft will be more widely separated (recall the "two fists" rule), but they will trace a much higher arc across the sky. Emerging from the Earth's shadow, about 15-degrees above the northwest horizon at 5:43 a.m. EST, Endeavour and the ISS will climb to a maximum altitude of 63-degrees above the northeast horizon at 5:45 a.m, then drop down toward the east-southeast horizon by 5:48. Overall, this pass should last 5 minutes 10 seconds! At their closest point (when highest in the sky), they should be about 240 miles away. If you're familiar with the constellations, they will appear to pass between the Big Dipper and Polaris (the North Star), then streak past the lozenge-shaped head of Draco, then, as they descend they will pass close to two of the brightest stars in the sky: Vega in Lyra and Altair in Aquila. Interestingly, the ground track for both vehicles shows that they will appear to pass directly overhead (or very nearly so) as seen from Catskill, NY in Columbia County.

Region of visibility

Generally speaking, the tandem will be visible across southern Canada and most of the 48 contiguous United States (Hawaii and Alaska will not have favorable viewing passes during this upcoming week).

Across southern Canada and the northern half of the United States there will be two or three morning viewing opportunities. For some favored locations, like Chicago and Milwaukee there will be as many as four opportunities. Over the southern United States, the viewing opportunities will be reduced to just one. Much of Florida (save for the Panhandle), central and southern Georgia, and parts of western and southern Texas will unfortunately be denied a view of the "dynamic duo" because they'll appear too low in the sky and too near to sunrise to be easily visible.

For other locations . . .

So what is the viewing schedule for your particular hometown? You can easily find out by visiting one of these three web sites:

• Chris Peat's Heavens Above
• NASA's SkyWatch
• Spaceweather.com

Each will ask for your zip code or city, and respond with a list of suggested spotting times. Predictions computed a few days ahead of time are usually accurate within a few minutes. However, they can change due to the slow decay of the space station's orbit and periodic reboosts to higher altitudes. Check frequently for updates.

Another great site is Real Time Satellite Tracking, which shows where the ISS or Space Shuttle are at any given moment during the day or night.

What to expect

Both vehicles will be traveling across North America on northwest-to-southeast trajectories.

A large telescope is needed to make out details of the sprawling station. Traveling in their respective orbits at approximately 18,000 mph (29,000 kph), both should be visible anywhere from about one to five minutes (depending on the particular viewing pass) as they glide with a steady speed across the sky.

Because of its size and configuration of highly reflective solar panels, the space station is now, by far, the brightest man-made object currently in orbit around the Earth.

On favorable passes, it approaches magnitude -5 in brightness, which would rival the planet Venus and is more than 25 times brighter than Sirius, the brightest star in the night sky. Some have even caught a glimpse of the ISS just prior to sunset or shortly after sunrise. And as a bonus, sunlight glinting directly off the solar panels can sometimes make the ISS appear to briefly flare in brilliance.

Other satellites too

The appearance of either the space shuttle or the space station moving across the sky is not in itself unusual. On any clear evening within a couple of hours of local sunset and with no optical aid, you can usually spot several orbiting Earth satellites creeping across the sky like moving stars. Satellites become visible only when they are in sunlight and the observer is in deep twilight or darkness. This usually means shortly after dusk or before dawn.

What makes the prospective upcoming passages so interesting is that you'll be able to see the two largest orbiting space vehicles in the sky at the same time.

Shuttle Endeavour is expected to undock from the ISS at 7:54 p.m. Eastern Standard Time on Friday. Endeavour will fly around the ISS before finally pulling away from the Station at 9:38 p.m. EST, although it should still remain at a relatively close distance to it until its scheduled return to the Kennedy Space Center in Florida Sunday evening.

On New Year's Eve the Full Moon will rise shortly after sunset—doing just what full moons are supposed to do. In this case, however, it'll be the second full moon in the calendar month of December. Whenever this occurs, recent tradition identifies it as a Blue Moon. The average time between full moons is about 29.5 days. So any month but February can, in principle, harbor a Blue Moon. If you do the math, you will see that somebody gets a Blue Moon every 2.7 years, or so. Not particularly rare—no one thinks of Presidential elections as rare, yet they take place less often than Blue Moons. The last Blue Moon on New Year's Eve was 1990.

The Moon can actually look blue during rare (polluting) atmospheric conditions that involve volcanic eruptions and forest fires.

Each Full Moon of the year has a name, mostly traceable to an era of agricultural living. Most famous among them is the "Harvest Moon" (nearest to the fall equinox), and the "Honey Moon" (June), but others include the "Sap Moon" (March), and the "Grain Moon" (August).

Times have changed, of course, which led me several years ago to update these Moon names with references more relevant to our modern culture. How about:

*Adapted from "Merlin's Tour of the Universe"

Happy New Year to all—'twas just another 584 million miles around the Sun.

-Neil deGrasse Tyson

If you missed out on last month's Leonid Meteor Shower, don’t fret. What potentially will be the best meteor display of the year is just around the corner, scheduled to reach its peak during the overnight hours of December 13-14: The Geminid Meteor Shower.

If the Geminids occurred during a warmer month, they would be as familiar to most people as the famous August Perseids. Indeed, a night all snuggled-up in a sleeping bag under the stars is an attractive proposition in summer, and many campers on vacation often independently “discover” the Perseids. On the other hand, it’s hard to imagine anything more bone chilling than lying on the ground in mid-December for several hours around midnight, looking up at a clear sky that has brought radiational cooling and plummeting temperatures since sunset.

But if you are willing to bundle up, this coming Sunday night into early Monday morning will be when the Geminids are predicted to be at their peak. And depending how dark your location is, and how much of the sky you can see, meteors may streak into view that night at an average rate of one or two per minute. The Geminids are—for those willing to brave the chill of a December night—a very fine winter shower, and usually the most satisfying of all the annual showers, even surpassing the Perseids.

Studies of past displays show that this shower has a reputation for being rich both in slow, bright, graceful meteors and fireballs as well as faint meteors, with relatively fewer objects of medium brightness. Many appear yellowish in hue. Some even appear to form jagged or divided paths.

These meteors appear to emanate from a point near the bright star Castor, in the constellation of Gemini, hence the name “Geminid.” The track of each one does not necessarily begin near Castor or even in the constellation Gemini, but it always turns out that the path of a Geminid extended backward passes through a tiny region of sky about 0.2 degrees in diameter (an effect of perspective). In apparent size, that’s less than half the width of the Moon. As such, this is a rather sharply defined radiant as most meteor showers go; suggesting the stream is “young”—perhaps only several thousand years old.

Excellent Viewing Conditions

Unlike the case this year with the August Perseids, this year’s December Geminids will not be hindered at all by moonlight. On Monday morning, the Moon—a narrow sliver of a crescent, just two days before New—will come up over the east-southeast horizon soon after 5:30 a.m. for most locations and will pose very little, if any interference for meteor watchers.

Best of all, Earth is predicted to be passing through the densest part of the Geminid swarm at around 5:00 GMT on December 14. That means that much of Europe and North America will be in excellent position to catch the absolute peak of this display, which should persist for more than several hours. Keep in mind that regardless of where you live, the very best time to watch for the Geminids will come at 2 a.m. local time on Monday morning. At that hour, the constellation Gemini will appear almost directly overhead.

Late Sunday night on through early Monday morning, a single observer blessed with a dark and unobstructed view of the sky might average as many as 60 to 120 meteors per hour —one to two meteor sightings per minute.

Watch for Earthgrazers

Generally speaking, depending on your location, the star Castor begins to come up above the east-northeast horizon right around the time evening twilight is coming to an end. As Gemini is beginning to climb the eastern sky just after darkness falls, there is a fair chance of perhaps catching sight of some “Earth-grazing” meteors early on Sunday evening.

Earthgrazers are long, bright shooting stars that streak overhead from a point near to, or even just below, the horizon. Such meteors are so distinctive because they follow very long paths nearly parallel to our atmosphere. As Gemini climbs higher into the sky, however, these very long paths will become much shorter.

The Geminids will appear noticeably more numerous in the hours after 10 p.m. local time, because the shower’s radiant is already fairly high in the eastern sky by then. As was already noted, the best views come at around 2 a.m., when their radiant point will be passing very nearly overhead. The higher a shower’s radiant, the more meteors it produces all over the sky.

Slowpokes

Because Geminid meteoroids are several times denser than the cometary dust flakes that supply most meteor showers and because of their relatively slow speed with which they encounter Earth—22 mi (35 km) per second—Geminid Meteors appear to linger a bit longer in view than most. As compared to an Orionid or Leonid meteor that can whiz across your line of sight in less than a second, a Geminid meteor moves only about half as fast.

Slow rise . . . rapid decline

The Earth moves quickly through this meteor stream producing a somewhat broad, lopsided activity profile. Hourly rates begin to slowly increase on December 10, when hourly rates will be about one-quarter maximum rates.

After Sunday night, their intensity should drop off more sharply: rates on Monday night/Tuesday morning will have diminished to about 30 to 60 per hour. Yet, there is good reason to keep watching for Geminids even after their peak has passed, for those “late” Geminids, tend to be especially bright. And renegade late stragglers might be seen for a week or more after the night of maximum activity.

Stay warm and "Shower" with a Friend

I brought this up this point earlier, but certainly it should be addressed again: Make sure you're warm and comfortable. Likely your local weather will be more appropriate for taking in a hot bath as opposed to a meteor shower! Meteor watching in December can be a long, cold business. You wait and you wait for meteors to appear. If they don't appear right away, and if you're cold and uncomfortable, you're not going to be looking for meteors for very long!

The late Henry Neely, who for many years served as a popular lecturer at New York’s Hayden Planetarium, once had this to say about watching for the Geminids: “Take the advice of a man whose teeth have chattered on many a winter’s night—wrap up much more warmly than you think is necessary!” Hot cocoa, tea or coffee can take the edge off the chill, as well as provide a slight stimulus.

It's even better if you can observe with a friend. That way, you can keep each other awake, as well as cover more sky. Give your eyes time to dark-adapt before starting.

Asteroid or Dead Comet?

A final point to note are that Geminids stand apart from the other meteor showers in that they seem to have been spawned not by a comet, but by 3200 Phaeton, an Earth-crossing asteroid. Then again, the Geminids may be comet debris after all, for some astronomers consider Phaeton to really be the dead nucleus of a burned-out comet that somehow got trapped into an unusually tight orbit.