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BAA Observing calendar

Asteroid 3 Juno at opposition

Thursday, 2018, November 15 - 03:14

Dominic Ford – originally published on In-The-Sky.org

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

Regardless of your location on the Earth, 3 Juno will reach its highest point in the sky at around midnight local time.

From London (click to change), it will be visible between 21:14 and 03:06. It will become accessible at around 21:14, when it rises 23° above your south-eastern horizon, and then reach its highest point in the sky at 00:12, 35° above your southern horizon. It will become inaccessible at around 03:06 when it sinks to 24° 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 3 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 3 Juno lies opposite to the Sun in the night sky, the solar system is lined up so that 3 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 3 Juno.

On this occasion, 3 Juno will pass within 1.035 AU of us, reaching a peak brightness of magnitude 6.9. Nonetheless, even at its brightest, 3 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.

Finding 3 Juno

The star charts below mark the path of 3 Juno across the sky around the time of its opposition.

This star chart is also available as a PDF download, or in a light-on-dark color scheme (large image, small image or PDF download).

The exact position of 3 Juno at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 3 Juno 03h48m20s -03°25' Eridanus 6.9

The coordinates above are given in J2000.0.


The details of this observing event were provided courtesy of In-The-Sky.org

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