If the weather is clear tonight, we invite you to go outside one to two hours after sunset and gaze upwards.
If you are lucky enough to sit far away from bright light, grab a long lounge or recliner and sit comfortably. Once your eyes have fully adjusted to the dark, you may be able to count several hundred stars of varying degrees of brightness.
But you might also see some other interesting sights, including the largest and brightest object now orbiting Earth: the International Space Station.
Related: Track the ISS: how and where to see it
You might catch a glimpse of an alien invader; a sudden streak of light that lasts no more than a second or two and may leave a short glowing trail.
Ancient stargazers believed that such a sight was a star falling from its fixed position in the sky. Today we call these meteors, although the terms "shooting star" and "shooting star" are still widely used. Such objects are usually particles no larger than a pebble or grain of sand, which enter our upper atmosphere at high speeds of up to 72 km per second; their kinetic energy is converted into light almost instantly, creating the effect of a shooting star. Most meteors first appear at an altitude of 80 miles (130 km) and disappear about a second later at perhaps 40 miles (65 km).
Then there's another group of invaders that have been with us since the dawn of the Space Age, some 67 years ago: artificial satellites.
Unlike meteors, they are much larger: actually man-made structures that orbit our Earth and orbit our home planet at an average speed of "only" 5 miles per second.
Perhaps the best visual description of a satellite is that of the late British satellite observer Desmond King-Hele (1927-2019). In his excellent book "Observing Earth's Satellites" (Van Nostrand Reinhold Company, 1983) he wrote: "A satellite looks like a star that has said goodbye to its senses and decided to move to another part of the sky."
Satellites are seen at night because their metal skins are illuminated by the sun. A satellite that enters the Earth's shadow immediately disappears from view, following an invisible path until it emerges again into full sunlight.
How many?
Right now, if you carefully study the sky between 30 minutes and two hours after sunset, or between two hours and 30 minutes before sunrise, chances are you will see as many as 15 to 30 satellites, varying in brightness. from as bright as the brightest stars (zero or first magnitude) to moderately faint objects of about fourth magnitude. This shouldn't be too surprising considering how many objects are now orbiting the Earth.
The very first satellite was Sputnik 1, launched in October 1957. Since then, there are now approximately 9,500 satellites in orbit around the Earth. Most of these are active charges, but there are also 100 million pieces of "space junk," ranging in size from as large as 30 feet to about the size of a softball, and literally millions of smaller pieces that could nonetheless prove disastrous if they hit another object in orbit. The US Space Command in Colorado Springs, Colorado, continuously monitors all flying debris.
Most satellites are too faint to see with the naked eye. But depending on who's counting, several hundred or more could be seen with the naked eye. These are the satellites that are large enough (more than 20 feet or 6 meters long) and low enough (100 to 400 miles or 160 to 640 km above Earth) to be most easily seen.
The biggest!
TOP TELESCOPE CHOICE:
Looking for a telescope to see the ISS in the night sky? We recommend the Celestron Astro Fi 102 as the top choice in our best telescope for beginners guide.
By far the largest and brightest of all man-made objects orbiting Earth is the International Space Station (ISS), which was assembled and currently maintained by the United States, Russia, the European Space Agency, Japan, and Canada . The station's solar panels are 73 meters wide, equivalent to the wingspan of a Boeing 777. The station itself is 108 meters long, or just one meter away from the entire length of a football field, including the end zones. It weighs 925,335 pounds (462.7 tons).
As it orbits the Earth at an average altitude of 420 km and at a speed of 28,200 km per hour, it can appear as fast as a high-flying jet aircraft, sometimes taking six or more seconds. seven minutes to cross the air. It can easily be confused with aircraft lights.
Nominally it appears white with a slight yellow tinge and nominally its visual magnitude can reach a brilliant -1.8 (rivaling with Sirius, the brightest star in the night sky), although at its very brightest it can sometimes appear as bright as magnitude -5.6, that is twice as bright as the planet Venus!
Although the ISS looks like a very bright moving star to the naked eye, those who have been able to train a telescope on it have actually been able to detect the T-shape as it zooms across their field of view. Some have actually managed to track the ISS with their range by moving it along the projected path. Those who have gotten a good glimpse describe the space station's casing as brilliant white, while the solar panels appear coppery red.
Simply put, when the ISS moves through your sky, it's virtually impossible to miss it!
Many windows of opportunity
From now until the end of May, North Americans will have many opportunities to see the ISS flying over their homes, mainly due to seasonal conditions. As we approach the summer solstice on June 20, nighttime hours are getting shorter and the time that a low-Earth orbit satellite (such as the ISS) can remain illuminated by the sun may extend well into the night, a situation that never be achieved during other times of the year.
Because the ISS orbits the Earth on average about every 90 minutes, this means it is possible to see it not just during a single pass, but over several consecutive passes.
For most locations, two types of passes are visible. In one case, the ISS initially appears toward the southwestern part of the sky and then moves toward the northeast. But on other occasions it becomes possible to see a second kind of pass, where the ISS initially appears towards the northwestern part of the sky and then moves towards the southeast.
In the most extreme cases, you might be able to catch the ISS four or more times in one day!
Example: From New York City on Friday, May 10, the ISS will take about 3.5 minutes to pass low over the north-northeast horizon from north-northwest to northeast, beginning at 2:08 a.m. EDT. A slightly higher pass, which follows a northwest to east-southeast trajectory and takes almost 5 minutes, starts at 3:44 am. Later that evening, at 10:01 PM, a noticeably higher, brighter and longer pass begins in the west. southwest and ends almost 7 minutes later in the northeast. Along the way, the ISS will climb two-thirds of the way up the north-northwest horizon to the point directly overhead.
Later that same evening, the ISS will make a much lower pass from 11:39 PM, taking 2 minutes to track from west-northwest to north-northwest. The ISS will then quickly fade as it enters the Earth's shadow.
Where and when should you look?
So, what's the viewing schedule for your specific hometown? You can easily find out by visiting one of three popular websites:
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Find the station - This site tells you when and where you can see the ISS. All you have to do is type in your city or town and then click on the map to see all the details. You can even sign up to receive email or text alerts when the space station flies overhead.
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Chris Peat's heaven above - This site provides you with observational information not only for the ISS, but also for Tianhe-1. You must first register and then enter your location to generate a sighting schedule.
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Live real-time satellite tracking - Like Heavens Above, you can get observational information for both the ISS and Tianhe-1. Once you log in, this site automatically provides data based on your IP address, or you can set a "custom" location.
Forecasts calculated a few days in advance are usually accurate within a few minutes. However, they may change due to the slow decay of the space station's orbit and periodic re-boosts to higher altitudes. Check for updates regularly.
Clear skies and happy hunting!
Joe Rao is an instructor and guest lecturer in New York Hayden Planetarium. He prescribes on astronomy Natural history magazinethe Farmer's almanac and other publications.
