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Asteroid 15 Eunomia at opposition

Dominic Ford, Editor
From the Asteroids feed

Objects: 15 Eunomia
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The sky at

Asteroid 15 Eunomia will be well placed, 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 around midnight local time.

From Fairfield, it will be visible between 21:13 and 04:27. It will become accessible around 21:13, when it rises to an altitude of 21° above your south-eastern horizon. It will reach its highest point in the sky at 00:52, 42° above your southern horizon. It will become inaccessible around 04:27 when it sinks below 21° above your south-western horizon.

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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 8.2. Nonetheless, even at its brightest, 15 Eunomia is a faint object beyond the reach of the naked eye; binoculars or a telescope of moderate aperture are needed.

Finding 15 Eunomia

The chart below indicates the path of 15 Eunomia across the sky around the time of opposition.

It was produced using StarCharter and is available for download, either on dark background, in PNG, PDF or SVG formats, or on a light background, in PNG, PDF or SVG formats.

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

Object Right Ascension Declination Constellation Magnitude
Asteroid 15 Eunomia 21h19m10s -05°56' Aquarius 8.2

The coordinates above are given in J2000.0.

The sky on 12 August 2019
Twilight ends
Twilight begins

11-day old moon
Waxing Gibbous


11 days old

Rise Culm. Set
Mercury 04:27 11:42 18:56
Venus 05:55 12:58 20:00
Moon 18:29 23:10 02:58
Mars 06:33 13:26 20:19
Jupiter 15:41 20:21 01:05
Saturn 17:53 22:32 03:16
All times shown in EDT.


The circumstances of this event were computed from orbital elements made available by Ted Bowell of the Lowell Observatory. The conversion to geocentric coordinates was performed using the position of the Earth recorded in the DE405 ephemeris published by the Jet Propulsion Laboratory (JPL).

The star chart above shows the positions and magnitudes of stars as they appear in the Tycho catalogue. The data was reduced by the author and plotted using PyXPlot. A gnomonic projection of the sky has been used; celestial coordinates are indicated in the J2000.0 coordinate system.

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