Asteroid 15 Eunomia at opposition

2019 Aug 12

Asteroid 15 Eunomia will be well placed for observation, lying in the constellation Aquarius, well above the horizon for much of the night.

Regardless of your location on the Earth, 15 Eunomia will reach its highest point in the sky at around midnight local time.

From London, it will be visible between 22:04 and 03:47. It will become accessible at around 22:04, when it rises 21° above your south-eastern horizon, and then reach its highest point in the sky at 00:58, 32° above your southern horizon. It will become inaccessible at around 03:47 when it sinks to 22° 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 15 Eunomia 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 15 Eunomia lies opposite to the Sun in the night sky, the solar system is lined up so that 15 Eunomia, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 15 Eunomia.

On this occasion, 15 Eunomia will pass within 1.409 AU of us, reaching a peak brightness of magnitude 8.3. Nonetheless, even at its brightest, 15 Eunomia 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 15 Eunomia

The star charts below mark the path of 15 Eunomia across the sky around the time of its opposition.

This star chart is also available to download:

Light-on-dark PNG image PDF document
Dark-on-light PNG image PDF document

The exact position of 15 Eunomia at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 15 Eunomia 21h18m10s -06°03' Aquarius 8.3

The coordinates above are given in J2000.0.

This entry in the observing calendar was provided by