Asteroid 532 Herculina at opposition

2015 May 19

Dominic Ford – originally published on

Asteroid 532 Herculina will be well placed for observation, lying in the constellation , well above the horizon for much of the night.

Regardless of your location on the Earth, Herculina will reach its highest point in the sky at around midnight local time.

From London (click to change), it will be visible all night. It will become visible at around 22:41 (GMT) as the dusk sky fades, 31° above your south-eastern horizon. It will be lost to dawn twilight at around 03:06, 34° above your south-western horizon.

The geometry of the alignment

This optimal positioning occurs when it makes its closest approach to the point in the sky directly opposite to the Sun – an event termed opposition. Since the Sun reaches its greatest distance below the horizon at midnight, the point opposite to it is highest in the sky at the same time.

At around the same time that Herculina passes opposition, it also makes its closest approach to the Earth – termed its perigee – making it appear at its brightest in the night sky. This happens because when Herculina lies opposite to the Sun in the night sky, the solar system is lined up so that Herculina, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as Herculina.

On this occasion, Herculina will pass within 1.452 AU of us, reaching a peak brightness of magnitude 8.5. Nonetheless, even at its brightest, Herculina is a faint object beyond the reach of the naked eye or binoculars; a telescope of moderate aperture and a good star chart are needed.

The exact position of Herculina at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 532 Herculina 15h57m10s +01°25′   8.5

The coordinates above are given in J2000.0.

The details of this observing event were provided courtesy of