On Tuesday (Sept. 8, 2009) and Wednesday (Sept. 9, 2009) the New York metro area will have three great opportunities (local weather conditions permitting) to see the Space Shuttle Discovery and the International Space Station flying in tandem across our evening sky.

Currently, Discovery is docked to the Space Station, but at 3:27 p.m. on Tuesday it will undock from the Station and slowly begin to pull away from it.

On Tuesday, at 7:42 p.m., both Discovery and the Space Station will rise above the SSW horizon and will track toward the ENE. They will appear as two bright moving "stars." Discovery will appear to lead the Space Station across the sky. The Space Station, however, should appear as the brighter of the two objects. They will be separated by roughly 5 or 6 degrees; your clenched fist held at arm's length measures roughly 10-degrees, so the Shuttle and Space Station will be separated by about a "half fist" as they move across the sky. At their highest point, they will stand 33-degrees above the SE horizon and at 7:44:30, as an added bonus, they will pass directly above the planet Jupiter. This pass should take 5 minutes 17-seconds from start to finish.

Also on Tuesday evening, a second pass will begin at 9:18 p.m. Discovery and the Space Station will appear a little farther apart. They will rise above the W horizon and will track toward the NNW. After 2 minutes 29 seconds, however, they will rapidly fade out, 25-degrees above the horizon, as they pass into the Earth's shadow.

On Wednesday, comes the third and final double pass. The two space vehicles will be much farther apart ... the Shuttle will lead the ISS by about one minute. Watch for Discovery at 8:05 p.m. rising above the WSW horizon, moving toward the NE; the Space Station will follow along the same track about a minute later. At their highest point, they will stand 64-degrees above the NW horizon. This pass should take 5 minutes 42-seconds from start to finish.

Discovery is scheduled to return to the Kennedy Space Center in Florida on Thursday (Sept. 10) at 7:06 p.m.

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.

When I was a youngster growing up in the Throggs Neck section of The Bronx, the Hayden Planetarium had a service called Dial-a-Satellite.  When you called a special phone number, you could hear a recorded message telling you when and where to look for the brightest naked-eye satellites that occasionally tracked across our local New York skies.  Back then (and I'm speaking now about the mid-1960s) the only really bright satellites readily visible were actually two giant Mylar balloons... measuring about 100-feet in diameter which orbited Earth at altitudes of about 1000 miles.

These were the Echo passive communications satellites: they actually functioned as reflectors, not transmitters. After being placed in orbit around the Earth, a signal would be relayed to one of the two Echo satellites, which were reflected or bounced off its surface, then returned to Earth. The Echo satellites were easily visible to the eye because of their highly reflective surface, but also because of their low orbits; they would appear from below one side of the horizon, cross the sky, then disappear below the opposite horizon after crossing the sky, as happens with all low Earth orbiting satellites. These spacecraft were nicknamed satelloons by those involved in the project. Today, those two Echo satellites are long-gone, but there are now literally thousands of satellites orbiting our Earth.

By far and away, the biggest object now orbiting our Earth is the International Space Station.  And if our skies are reasonably clear on Saturday, November 22, we here in the Tri-State Area will have a great opportunity to see the ISS make a long, high pass across the evening twilight sky.

It will be moving along a track that will take it roughly from Washington to just north of New York and then on toward Boston and the Gulf of Maine; it will briefly overfly our region about an hour after sundown.

It always amazes people when they are told that they can actually see the Space Station—now orbiting 218 miles above Earth—with their own two eyes; no optical aid is needed.  As big as a football field, the ISS is visible by virtue of sunlight shining on its metallic skin and large solar panels.  To the unaided eye it appears as a very bright star that does not twinkle and shines with a slight yellowish-white tinge. Check out this short video of it when it passed over Gloucester, Massachusetts back on Christmas Eve, 2006.

Some assiduous astronomers have even been able to photograph the actual structure of the Space Station by tracking it with their telescope:

On Saturday, the ISS will emerge from above the southwest horizon at 5:32 p.m. Prepare yourself for this ISS pass by getting outside some minutes before it's due to appear and getting yourself acclimated to the sky and the surrounding stars.  Certainly, you will immediately notice two very bright, non-twinkling silvery stars low in the southwest.  They are not stars, but planets; the brighter and lower of the two is Venus, the other will be Jupiter.  Make a fist and hold it out at arm's length.  When the ISS first appears, it should be roughly "two fists" to the right of Jupiter and Venus.  It will appear to move straight up to a point almost directly overhead.  It will then drop down toward the northeast, disappearing about 3-minutes after it first appeared, near to the northeast horizon.  It actually will seem to rapidly fade out toward the end of its track as it moves into the Earth's shadow.

As to just how bright it should get, it should be plainly visible even from brightly lit cities; only Venus and perhaps Jupiter will be brighter.  So during it's 3-minutes of visibility, the Space Station will be one of the three brightest objects in the sky!

And keep in mind that as you look at it, there are ten people who are currently onboard.  Three are semi-permanent residents, staying for upwards of six months on the ISS.  The other seven just recently arrived on the Space Shuttle Endeavour which was launched from Florida on November 14.  The Shuttle is currently docked to the ISS and is scheduled to return to Earth on November 29.

Pretty neat, huh? Tell all your neighbors... and take the kids out for a look.

I'll be interested to see how many plan to check it out, so drop me a line if you see it.