If you go out and carefully study the sky near dusk or dawn, and you have relatively dark skies, the odds are that you should not have to wait more than 15 minutes before you see one of the nearly 15,000 satellites now in orbit around Earth. Most of these "satellites" are actually just "space junk" ranging in size from as large as 30 feet, down to about the size of a softball. The Joint Space Operations Center (JSpOC) headquartered at Vandenberg AFB in California, keeps a constant watch on all orbiting debris. And in fact most satellites—especially the bits of debris—are too faint to be seen with the unaided eye. But depending on who's counting, several hundred can be spotted with the unaided eye. These are the satellites that are large enough (typically more than 20 feet in length) and low enough (100 to 400 miles above Earth) to be most readily seen a sunlight reflects off them.

The biggest

The International Space Station (ISS) is by far the biggest and brightest of all the man-made objects orbiting the Earth. On-orbit construction of the station began in 1998, and is scheduled to be complete by 2011, with operations continuing until around 2015. More than four times as large as the defunct Russian Mir space station, the completed International Space Station will ultimately have a mass of about 1,040,000 pounds (520 tons) and will measure 356 feet across and 290 feet long, with almost an acre of solar panels to provide electrical power to six state-of-the-art laboratories. Presently circling the Earth at an average altitude of 216 mi (348 km) and at a speed of 17,200 mi (27,700 km) per hour, it completes 15.7 orbits per day and it can appear to move as fast as a high-flying jet airliner, sometimes taking about four to five minutes to cross 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 can appear as bright as the planet Venus, at magnitude -4.5, and some 16 times brighter than Sirius, the brightest star in the night sky. Some have made estimates as bright as magnitude -5 or -6 for the station (smaller numbers represent brighter objects on this astronomers scale). And as a bonus, sunlight glinting directly off the solar panels can sometimes make the ISS appear to briefly "flare" in brilliance to as bright as magnitude -8; more than 16 times brighter than Venus!

Other things to see

Along with the ISS, you can also look for a space shuttle on those missions when one is approaching or departing from the space station. Also visible to the naked eye is the newly refurbished Hubble Space Telescope. And with good binoculars, you might also try sighting the infamous "ISS Toolbag" which accidentally was allowed to drift into space when veteran spacewalker and astronaut Heide Stefanyshyn-Piper lost her grip on the backpack-sized bag last Nov. 18

Viewing opportunities

From now through the final days of July, North Americans and Europeans will have many opportunities to see the ISS flying over their homes, due chiefly to a seasonal circumstance. Nights are now the shortest and the time that a satellite in a low-Earth-orbit (like the ISS) can remain illuminated by the Sun can extend throughout the night, a situation that can never be attained during other times of the year. Because the ISS circles the Earth about every 90 minutes on average, this means that it's possible to see it not just on one singular pass, but for several consecutive passes. Moreover, because the ISS revolves around the Earth in an orbit that is inclined 51.6-degrees to the equator, there are two types of passes that are visible. In the first case (we'll call it a "Type I" pass), the ISS initially appears over toward the southwestern part of the sky and then sweeps over toward the northeast. About seven or eight hours later, it becomes possible to see a second type of pass (we'll call it "Type II"), but this time with the ISS initially appearing over toward the northwestern part of the sky and sweeping over toward the southeast. During these next several weeks, Type I passes will initially be visible in the morning hours, prior to sunrise. By early July, Type I passes will be visible during the evening hours, just after sunset, while Type II passes will be occurring in the early morning. By late July, visibility of the Type II passes will have shifted into the evening hours. FROM NEW YORK CITY the best ISS passes in July will be Type II. If you are an early riser, there will be two excellent dawn passes of the Space Station. In both cases, it will trace a high northwest to southeast path across the twilight sky. The first opportunity comes on July 6 from 4:43 to 4:48 a.m. There will be another, very similar pass two mornings later on July 8 between 3:56 and 4:02 a.m. If these times are too early for you, then just wait a couple of weeks and the ISS will make two similarly high NW to SE passes during the evening hours. On July 23, it will be visible between 9:44 and 9:48 p.m. and two evenings later you'll see it moving along the same NW to SE path between 8:58 and 9:03 p.m. Of course there will be many other opportunities to see the ISS during July, but at lower altitudes and for shorter durations.

When and where to look

So what is the viewing schedule for your particular hometown? You can easily find out by visiting one of these four popular web sites: Chris Peat's Heavens Above Science@NASA's J-Pass 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 this one: http://www.n2yo.com/?s=25544 Which provides real-time satellite tracking and shows you at any given moment during the day or night over what part of the Earth the ISS happens to be.

Viewing tips

Some passes are superior to others. If the ISS is not predicted to get much higher than 20-degrees above your local horizon, odds are that it will not get much brighter than second or third magnitude (10-degrees is roughly equal to the width of your fist held at arm's length). In addition, with such low passes, the ISS will likely be visible for only a minute or two. Conversely, those passes that are higher in the sky—especially those above 45-degrees—will last longer and will be noticeably brighter. The very best viewing circumstances are those that take the ISS on a high arc across the sky about 45 to 60 minutes after sunset, or 45 to 60 minutes before sunrise. In such cases, you'll have it in your sky upwards to four or five minutes; it will likely get very bright and there will be little or no chance of it encountering the Earth's shadow. While the ISS looks like a moving star to the unaided eye, those who have been able to train a telescope on it have actually been able to detect its T-shape as it has whizzed across their field of view. Some have actually been able to track the ISS with their scope by moving it along the projected path. Those who have gotten a good glimpse describe the body of the Space Station as a brilliant white, while the solar panels appear a coppery red. For evening passes, the ISS will usually start out rather dim and then tend to grow in brightness as it moves across the sky. In contrast, for the morning passes, the ISS will already be quite bright when it first appears and will tend to fade somewhat toward the end of its predicted pass. This is due to the change in the angle of sunlight hitting the vehicle. Lastly, remember that in certain cases, the ISS will either quickly disappear when it slips into the Earth's shadow (during evening passes) or quite suddenly appear when it slips out of the Earth's shadow (during morning passes). This becomes increasingly more likely for passes that take place more than 90 minutes after sunset or more than 90 minutes before sunrise.

Should a rocket blast off on schedule early Tuesday evening, May 5, 2009, from NASA's Wallops Island Flight Facility in Virginia, a potentially spectacular sight might be visible across a wide swath of the U.S. Eastern Seaboard.

It would be only the fourth attempt at launching an orbital rocket from this coastal Virginia range—located just south of Assateague Island—in the last 13 and a half years. The first time NASA attempted an orbital launch from Wallops, in October 1995, the liftoff of a 50-foot-tall Conestoga rocket ignited normally, but the vehicle exploded over the Atlantic just 46-seconds later. A problem with the rocket’s guidance system was blamed.

Then in December 2006, a 69-foot, 5-foot wide, 35-ton, four-stage Minotaur I rocket successfully launched the TacSat-2 satellite, carrying a semisecret payload from the Pentagon's Missile Defense Agency. In April 2007, a Minotaur rocket sent the NFIRE satellite into orbit.

Now another Minotaur I rocket awaits liftoff from the Wallops Flight Facility next Tuesday evening, no earlier than 8:00 p.m. EDT. The chief goal of this flight is to place the 880-pound TacSat-3 satellite with its trio of payloads that will offer real-time imagery (within 10-minutes of collection), sea-based information transmitted from ocean buoys and plug-and-play avionics to assist warfighters in keeping one step ahead of their adversaries. In addition, three cubesats will be launched as secondary payloads on the TacSat-3 mission.

A launch window from May 5 to 9, from 8:00 p.m. to 11:00 p.m. EDT each day, has been established to take into account bad weather or equipment glitches (see Final Points below). A launch after 8:00 p.m. EDT would occur just after sunset along the entire Atlantic Coastline.

What to expect

Over the years, similar rocket firings have routinely taken place from California's Vandenberg Air Force Base. Rocket launches that have occurred around the time of sunrise or sunset have left long, glowing contrails in their wake that have been seen for a few hundred miles across the Desert Southwest; often becoming contorted by high level winds into strange and exotic patterns and sometimes, prismatic colors.

While many Westerners are fairly familiar with such sightings, they are all but unknown here in the East and as such may end up surprising millions of people should the Minotaur I lift off on schedule at 8:00 p.m. EDT or shortly thereafter on Tuesday evening.

Based on a very similar launch from Wallops Island in December 2006 and similar dusk and dawn launches from Vandenberg as a guide, I've determined that it should be possible that Tuesday's post-sunset launch may be visible as far north as southern Maine; as far south as northeastern Florida and as far west as eastern Kentucky. The rocket will be launched on a southeast trajectory. Approximately six minutes after launch it will be passing north of Bermuda. Three minutes later it will reach orbital altitude over the middle of the North Atlantic.

Observers who are situated within about 800 statute miles of the Wallops Island Flight Facility appear to have a reasonable chance of catching a view of the Minotaur I contrail within the first few minutes after launch.

The key to making a sighting is to have a clear, unobstructed view of the horizon in the direction of Wallops Island. For example, a viewer in Raleigh, North Carolina should look toward the northeast; in Boston, Massachusetts look southwest; in Wheeling, West Virginia it will be due east.

Areas farther to the northeast (toward southern New England) have an advantage since skies will be darker—sunset will come somewhat earlier than it will along the Mid-Atlantic Coast. At Wallops, it's at 7:57 p.m., but from Boston it's at 7:49 p.m.

Farther to the west, in the Ohio Valley, the Sun will still be above the horizon so the launch may only be barely visible, if at all against the blue daytime sky. But should the launch be delayed by just 30-minutes, sunset will arrive, sufficiently darkening local skies.

Final points

The Minotaur I is a launch vehicle sometimes called half man and half beast because it combines features of the Minuteman missiles and Pegasus rockets. It also merges space technologies designed for both military and commercial ventures.

Another factor in this launch is the upcoming May 11 launch of the Space Shuttle Atlantis at Cape Canaveral, Florida. According to Wallops Public Affairs officer Keith Koehler, the Wallops tracking systems are needed to support a shuttle Launch. We have to stand down because of the Space Shuttle launch on May 11. We have assets that support the launch. Then I believe there is another launch at the Cape that will be using assets that we use.

Wallops is NASA's cynosure for tracking orbital payloads and receiving meteorological information relating to North America. And although it has never been used for this purpose, Wallops can also boast that its 8,750-foot runway, usually reserved for winged-aircraft safety tests, is an approved shuttle emergency-landing site.

You can find more information on the launch, including the latest launch status and contact information, a webcast of the launch, and the countdown status on Twitter.

People in the eastern United States will get a great opportunity, weather permitting, to see the Space Shuttle Discovery launched into orbit Wednesday evening, March 11.

The Shuttle flight (STS-119) will be the 28th to rendezvous and dock with the International Space Station (ISS) and the glow of its engines will be visible along much of the Eastern seaboard of the United States.

To reach the ISS, Discovery must be launched when Earth's rotation carries the launch pad into the plane of the ISS's orbit. For mission STS-119, on March 11 that will happen at 9:20:10 p.m. ET, resulting in NASA's first Shuttle flight of 2009 and its second consecutive nighttime (the previous shuttle flight, last November 14, was also a nighttime launch). This launch will bring the Shuttle's path nearly parallel to the U.S. East Coast.

What to expect

For most locations, Discovery will be visible by virtue of the light emanating from its three main engines. It should appear as a very bright, pulsating, fast-moving star, shining with a yellowish-orange glow.

Based on previous night missions, the brightness should be at least equal to magnitude -2; somewhat brighter than Sirius, the brightest star in the sky, which shines brilliantly in the south-southwest during the evening hours. Observers who train binoculars on the Shuttle should be able to see the rapidly moving shuttle resembling a tiny V-shaped contrail.

In the Southeast United States, depending on a viewer's distance from Cape Canaveral, Discovery will become visible anywhere from a few seconds to 2 minutes after it leaves Pad 39-A. The brilliant light emitted by the two solid rocket boosters will be visible for the first 2 minutes and 4 seconds of the launch out to a radius of some 520 statute miles from the Kennedy Space Center.

No matter where you're located, keep in mind that the Shuttle will not get very high above the horizon. In most cases, it will range from roughly 5 to 10 degrees. To get an idea of how high this is, make a fist and hold it out at arm's length. Place the bottom of your fist on the horizon; the top of your fist is 10 degrees

By location:

Southeast U.S. coastline:

Anywhere north of Cape Canaveral, I suggest viewers initially concentrate on the south-southwest horizon (if you are south of the Cape, look low toward the north-northeast).

Mid-Atlantic region:

Look toward the south about 3 to 6 minutes after launch.

Northeast (Washington, Philadelphia, New York, Boston):

Concentrate your gaze low toward the south or south-southeast about 6 to 8 minutes after launch. Of course, as the shuttle gets closer, its azimuth very quickly swings over to the southeast, where in most cases, the point of maximum altitude occurs. I suspect most people will be scanning the horizon from south-southeast in the final couple of minutes of powered ascent . . . if so, you shouldn't miss out on sighting Discovery.

Discovery will seem to flicker, then abruptly wink-out 8 minutes and 23 seconds after launch as the main engines shut-down and the huge, orange, external tank is jettisoned over the Atlantic at a point about 870 statute miles uprange (to the northeast) of Cape Canaveral and some 430 statute miles southeast of New York City. At that moment, Discovery will have risen to an altitude of 341,600 feet (64.7 statute miles), while moving at more than 17,000 mph and should be visible for a radius of about 770 statute miles from the point of Main Engine Cut Off, or MECO.

Should the launch of Discovery be scrubbed on Wednesday, March 11, the launch will be rescheduled on a daily basis, but the time of the launch will occur roughly 23 minutes earlier for each day the launch is delayed (launch window times through March 16).

Before hoping to see the Shuttle streak across your local sky, make sure it has left the launch pad! Watch a television news outlet to verify that Discovery has been launched, or you can watch the launch on your computer via streaming video from NASA-TV.

Good Luck!