The International Space Station or ISS is now an easily seen daylight satellite, a white point of moving light especially easy to see from an airliner, and more like a large gliding silver star if the sun is low but still above the horizon.
Until recently it has been difficult but not impossible to find the ISS in broad daylight under perfect conditions but the completion of the expansive solar panels on the 108 metres by 73 metres city building sized satellite has made it much easier to spot.
And when another spacecraft is docked, during regular visits by the Space Shuttle, the Soviet Soyuz supply and manned craft, or the European Jules Verne ‘space truck’ it gets even brighter.
The space station is still gaining clip-on laboratory modules, with another made by Japan, due next month, but it is the huge solar panels that generate most of its brilliance.
Those panels are also springing surprises by ‘flaring’ into an incredibly bright moving star for several seconds if the angle between them, the sun, and observers on the ground just happens to become optimal. These flares cannot be predicted unlike those of the Iridium constellations of low orbit communications satellites.
But if one occurs at your observing point at night, when the ISS is still illuminated by the sun, the flare is reported to be as bright as -11 magnitude, which is bright enough to cast shadows against a light surface like concrete, a pale coloured wall or sand.
This is far more dazzling than Venus (which is currently visible as the morning star) at its best, or the occasional very bright flare thrown off an Iridium satellite when the sun is perfectly reflected off one of its highly polished antennas.
This is how to find the ISS in daylight using the free Heavens Above satellite tracking and general astronomy resource.
1. Find your GPS coordinates using a GPS unit or Google Earth, which will display the data when you put the cursor over your location. Also note your altitude if you want Heavens Above to be super accurate when it comes to other functions like rise and set times for the sun or planets.
2. Create a station on Heavens Above, entering the GPS data. Takes no time.
3. The Heavens Above site shows a moving map of where the ISS is, but once you have your own observing site set up (you can have as many as you like) it will also generate one click predictions of visible passes, meaning at night.
4. But you want it in daylight. Go to ‘select a satellite from the database’.
5. Enter ISS in the satellite name option as shown above.
6. Select ‘All Passes’ at the top right of the second page from there as shown above, to generate a table like this shown below.
7. From the table of all passes which will be above the horizon day or night from the base you have created, click on a daylight pass to generate a map (below) of the ground track by the minute showing the direction of the pass like the example in relation to my station on 21 June in the mid afternoon , which the map also shows will be nearly overhead if seen from Sydney.
You can also use a similar process to catch the ISS as a black dot, or as a detailed object using a telescope, if it transits the moon in the night sky when it would otherwise be invisible.
Heavens Above is an incredibly versatile astronomy resource with many layers worth exploring with or without a telescope.
CRITICALLY IMPORTANT WARNING: Do not look at or even near the sun with the naked eyes or sunglasses. NEVER LOOK DIRECTLY AT THE SUN. The ISS daylight naked eye passes of interest will never occur in close proximity to the sun anyhow.