© NASA/Galileo 1993. Pictured asteroid is 243 Ida.

Asteroid 15 Eunomia at opposition

Dominic Ford, Editor
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The sky at

Asteroid 15 Eunomia will be well placed for observation, lying in the constellation Centaurus, 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 Washington however, it will not be readily observable since it will lie so far south that it will never rise more than 20° above the 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 2.132 AU of us, reaching a peak brightness of magnitude 9.8. 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 14h40m00s -32°05' Centaurus 9.8

The coordinates above are given in J2000.0.

The sky on 08 May 2018
Sunrise
06:30
Sunset
20:27
Twilight ends
22:08
Twilight begins
04:50

22-day old moon
Waning Crescent

43%

22 days old

Planets
Rise Culm. Set
Mercury 05:35 11:56 18:18
Venus 08:08 15:30 22:52
Moon 02:56 08:12 13:27
Mars 01:34 06:24 11:14
Jupiter 20:16 01:34 06:46
Saturn 00:15 05:06 09:57
All times shown in MDT.

Source

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.

Image credit

© NASA/Galileo 1993. Pictured asteroid is 243 Ida.

Washington

Latitude:
Longitude:
Timezone:

37.13°N
113.51°W
MDT

Color scheme