I am often asked about the identity of unusually bright lights that people have spotted in the sky. More often than not, it is one of the bright planets Venus or Jupiter, or the brightest star in the sky, Sirius. However, sometimes the culprit is not stationary, but a star-like light that moves across the sky, or a point of light that spectacularly flares up to become exceptionally bright before gradually fading again.
The bright light that crosses the sky from a westerly to easterly direction is most likely the International Space Station, a man made space ship in orbit around the Earth at a height of 400 km. The Space Station isn’t visible every day, but its visibility occurs in bursts so it will be visible for a few days and then not visible for a while. It’s amazing to watch as this man made object with astronauts on board drifts silently across the sky.
Equally as spectacular, if not more so, are the flares mentioned above. The flares are caused by light from the Sun bouncing off the solar panels or flat antennae of a particular type of communication satellite as it orbits the Earth. The satellites are owned by Iridium Communications and so the flares are known as Iridium flares.
There are often 4 or 5 of these flares of varying brightness visible in an evening. On Monday the 26th June at 23:25:23 there will be a really bright flare in the west, 26 degrees above the horizon. It might be slightly different depending on your observing location. To see these Iridium flares and the International Space station you can search on the internet or download an app called Heavens Above which will give you precise times for your observing location.