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

Asteroid 2 Pallas at opposition

Mon, 23 Oct 2017 at08:27 EDT(86 days ago)
12:27 UTC

Dominic Ford, Editor
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The sky at

Asteroid 2 Pallas 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, 2 Pallas will reach its highest point in the sky at around midnight local time.

From Ashburn (click to change), it will be visible between 00:45 and 03:39. It will become accessible at around 00:45, when it rises 24° above your south-eastern horizon, and then reach its highest point in the sky at 02:12, 28° above your southern horizon. It will become inaccessible at around 03:39 when it sinks to 25° above your southern 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 2 Pallas 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 2 Pallas lies opposite to the Sun in the night sky, the solar system is lined up so that 2 Pallas, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 2 Pallas.

On this occasion, 2 Pallas will pass within 1.702 AU of us, reaching a peak brightness of magnitude 8.2. Nonetheless, even at its brightest, 2 Pallas 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 2 Pallas

The star charts below mark the path of 2 Pallas 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 2 Pallas at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Asteroid 2 Pallas 03h10m00s -22°41' Eridanus 8.2

The coordinates above are given in J2000.0.

The sky on 23 October 2017
Sunrise 07:26
Sunset 18:19
Twilight ends
Twilight begins

4-day old moon
Age of Moon
4 days

All times shown in EDT.
Rise Culm. Set
Mercury 08:18 13:30 18:42
Venus 05:51 11:44 17:37
Moon 10:58 16:00 21:02
Mars 04:58 11:03 17:09
Jupiter 07:38 13:03 18:29
Saturn 11:46 16:32 21:18


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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