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

Asteroid 3122 Florence at opposition

Tue, 29 Aug 2017 at20:26 EDT(141 days ago)
00:26 UTC

Dominic Ford, Editor
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The sky at

Asteroid 3122 Florence will be well placed for observation, lying in the constellation Capricornus, well above the horizon for much of the night.

Regardless of your location on the Earth, 3122 Florence will reach its highest point in the sky at around midnight local time.

From Ashburn (click to change), it will be visible between 21:43 and 01:25. It will become accessible at around 21:43, when it rises 24° above your south-eastern horizon, and then reach its highest point in the sky at 23:32, 30° above your southern horizon. It will become inaccessible at around 01:25 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 3122 Florence 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 3122 Florence lies opposite to the Sun in the night sky, the solar system is lined up so that 3122 Florence, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 3122 Florence.

On this occasion, 3122 Florence will pass within 0.053 AU of us, reaching a peak brightness of magnitude 9.0. Nonetheless, even at its brightest, 3122 Florence 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 3122 Florence

The star charts below mark the path of 3122 Florence 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 3122 Florence at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 3122 Florence 20h56m30s -20°43' Capricornus 9.0

The coordinates above are given in J2000.0.

The sky on 29 August 2017
Sunrise 06:35
Sunset 19:44
Twilight ends
Twilight begins

8-day old moon
Age of Moon
8 days

All times shown in EDT.
Rise Culm. Set
Mercury 06:17 12:45 19:13
Venus 03:53 11:02 18:11
Moon 14:22 19:27 00:32
Mars 05:40 12:30 19:20
Jupiter 10:18 15:57 21:36
Saturn 15:10 19:57 00:48


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.




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