major_clanger | Curse this cloudy weather!

Not because of that big shindig in central London today (indeed, the clouds have probably prevented an awful lot of sunburn). But today features in all likelihood the last chance to see another rare event: watching a Shuttle launch from the UK.

When the Shuttle flies to the International Space Station it launches on a trajectory north-east from Florida that results in it passing over the southern UK some 20 minutes after take-off. Most times this happens it is either daylight or fully dark here, so the Shuttle isn't visible from the ground. But if it's pre-dawn or post-dusk twilight, then it's possible for the Shuttle to be in sunlight as it passes over whilst on the ground it's dark enough to see it. Moreover, just after launch the Shuttle Orbiter is still accompanied by the large External Tank that will have been jettisoned some 10 minutes earlier. A year or two ago I actually saw this on an early morning launch, with the Orbiter and ET passing over as a bright white point of light together with an orange one about the width of the Moon apart.

Given that such conditions only apply to a fraction of Shuttle launches it's quite likely that this, the penultimate flight of the programme, will be the last time that such a sight can be seen from the UK. Endeavour is currently scheduled to take off at 8.47pm UK time so, if it flies on schedule, should be visible from most of the southern half of the UK some time around 9.05-9.10pm.

If the clouds shift, that is!

(The Shuttle has a narrow launch window every day - in effect, it must take off as Florida passes under the plane of the ISS's orbit. So if the launch is scrubbed, it will be rescheduled 24 or 48 hours. However, other factors mean that the launch window drifts a few minutes each day so that if it is delayed more than a few days it may go past the point at which the Shuttle will still be in sunlight as it flies over the UK.)