Four hundred-metre-wide asteroid 2015 TB145 passes just 302,500 miles (486,800 kilometres) or 1.3 lunar distances away from Earth on the evening of Saturday, 31 October 2015. There is no fear of a collision, but this is the closest approach by a known object this large until asteroid 1999 AN10 (800 metres in size) approaches at about 1 lunar distance (238,000 miles from Earth) in August 2027. According to predictions, Apollo-class asteroid 2015 TB145 could exceed 11th magnitude at its brightest on the evening of Saturday, 31 October as it passes closest to Earth at 5pm GMT.
Observing 2015 TB145 from the UK 30-31 October
As seen from the British Isles, the asteroid should therefore be within range of 6-inch aperture telescopes and larger from the onset of darkness on Friday, 30 October through to dawn twilight the following morning, despite the glow of a gibbous Moon in the sky. UK-based observers can then locate it again as darkness falls on Saturday night through to about 9pm GMT.
For observers with telescope mounts equipped with digital setting circles or computerised GoTo instruments, the following table lists J2000.0 topocentric coordinates of asteroid 2015 TB145 at hourly intervals for the centre of the British Isles. Since the asteroid is passing so close to Earth, there will be a small parallax displacement for those observers widely separated from the heart the UK.If you feel confident at using charts at the telescope, what follows is a ten-times enlargement of the naked-eye finder chart at the top of the page. Click the graphic for a greyscale version suitable for printing out for use at the telescope. Asteroid 2015 TB145 will be glimering at about magnitude +11.9 as it passes 5 arcminutes to the northwest of magnitude +4.4 star π2 Orionis close to 02:07 UT on Saturday, 31 October.