A glint of Sat-X and other gems (2)

Be apprised, that while binoculars and/or a telescope are good to have, you can enjoy satellite- watching without either. Viewing instruments are required for small spacecraft, like NigeriaSat-2 and Sat-X, and for geosynchronous satellites, such as NigComSat-1R.

But many manmade orbiters are easily accessible to the naked eye. “No equipment is needed,” advises David Dickinson, in Universe Today, “to start the hunt for satellites tonight, just a working set of eyes and information”.

“…On any clear evening,” concurs Space.Com, “within a couple hours of local sunset and with no optical aid, you can usually spot several orbiting…satellites creeping across the sky like moving stars”.

You’ve probably seen satellites, without knowing what they were. It’s easy to confuse them with “aircraft”. But aircraft have blinking lights. Satellites do not. Nor do they appear stationary, except through binoculars or a telescope.

This needs to be stressed, because Nigerians tend to identify any unusually bright and unmoving celestial body as a “satellite”. Actually, a satellite has to be moving west to east, at 36,000 km up, to appear stationary.

At this altitude, the spacecraft revolves at Earth’s rotational velocity—and thus has a 24-hour periodicity, which causes it to “stand still,” with respect to a surface-bound observer.

A geostationary (or geosynchronous) spacecraft is far out of naked-eye range. Consequently, any large luminous body, that lacks apparent motion, must be either a planet or a very bright star.

According to Space.Com, satellites become visible only when they are in sunlight and the observer is in deep twilight or darkness—which usually means shortly after dusk or before dawn. Visibility depends mainly (but not totally) on the spacecraft’s size, reflectivity and altitude.

In “Observing Man-Made Earth Satellites,” an Internet article, William Robert Johnston notes that visible spacecraft are in low Earth orbit (LEO), between altitudes of 150 km and 800 km. One trip around the planet, at these heights, takes 90 minutes to two hours.

Undoubtedly, the most widely observed artificial satellite is the International Space Station (ISS), which is visible from 95 percent of Earth’s surface (excluding the Polar Regions). It maintains an orbital altitude of between 330 and 435 km, Wikipedia reports, and completes 15.54 orbits per day.

I’d be surprised, if there are more than a few readers who haven’t seen ISS. It is a brilliant, unblinking dot that passes slowly overhead and can in clear skies remain visible for several minutes.

The Space Station may look small, in the sky. But it is actually bigger than a football field, with reflective solar panels and modules that flare in the sunlight. NASA will send a text or an email alert, when ISS is due to fly over your area. Just go to “Spot The Station” and fill out the form.

In the meantime, Sat-Flare also contains a 2011 FPAS report on China’s Tiangong-1: The first module of a planned 60-tonne space station. Its brightness was “steady,” at magnitude 2.2—well within naked-eye range, yet much dimmer than ISS’s “-4”.

As far as I know, China does not send out satellite alerts. But you should be able to get the local observation times from Sat-Flare or some of the other Online tracking sites.

Among non-crewed satellites, the Iridium constellation is legendary. It consists of 66 orbiting spacecraft (plus spares), whose antennas have a certain shape, which reflects sunlight in a way that creates “iridium flares”.

Says Wikipedia, “the satellite momentarily appears as one of the brightest objects in the night sky and can even be seen during daylight”.

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