Asteroid 3 Juno at opposition

2015 Jan 30

Dominic Ford – originally published on

Asteroid 3 Juno will be well placed for observation, lying in the constellation Hydra, well above the horizon for much of the night.

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

From London (click to change), it will be visible between 20:19 and 03:29. It will become accessible at around 20:19, when it rises 24° above your south-eastern horizon, and then reach its highest point in the sky at 23:52, 42° above your southern horizon. It will become inaccessible at around 03:29 when it sinks to 25° 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 Juno 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 Juno lies opposite to the Sun in the night sky, the solar system is lined up so that Juno, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as Juno.

On this occasion, Juno will pass within 1.34 AU of us, reaching a peak brightness of magnitude 7.8. Nonetheless, even at its brightest, Juno 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 Juno at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 3 Juno 08h31m20s +03°47′ Hydra 7.8

The coordinates above are given in J2000.0.

The details of this observing event were provided courtesy of