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

Dwarf Planet 1 Ceres at opposition

Dominic Ford, Editor
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The sky at

Dwarf Planet 1 Ceres will be well placed for observation, lying in the constellation Cancer, well above the horizon for much of the night.

Regardless of your location on the Earth, 1 Ceres will reach its highest point in the sky at around midnight local time.

From Ashburn, it will be visible in the morning sky, becoming accessible at around 18:57, when it rises 21° above your north-eastern horizon. It will then reach its highest point in the sky at 00:41, 81° above your southern horizon. It will be lost to dawn twilight at around 06:09, 24° above your 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 1 Ceres 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 1 Ceres lies opposite to the Sun in the night sky, the solar system is lined up so that 1 Ceres, the Earth and the Sun lie in a straight line with the Earth in the middle, on the same side of the Sun as 1 Ceres.

On this occasion, 1 Ceres will pass within 1.599 AU of us, reaching a peak brightness of magnitude 6.8. Nonetheless, even at its brightest, 1 Ceres 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 1 Ceres

The star charts below mark the path of 1 Ceres 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 1 Ceres at the moment of opposition will be as follows:

Object Right Ascension Declination Constellation Magnitude
Dwarf Planet 1 Ceres 09h13m10s +30°06' Cancer 6.8

The coordinates above are given in J2000.0.

The sky on 31 January 2018
Twilight ends
Twilight begins

14-day old moon
Waxing Gibbous


14 days old

Rise Culm. Set
Mercury 06:49 11:36 16:24
Venus 07:40 12:45 17:50
Moon 18:07 00:01 07:06
Mars 02:36 07:30 12:25
Jupiter 01:36 06:42 11:48
Saturn 05:01 09:46 14:31
All times shown in EST.


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.

Related news

21 Oct 2016, 00:39 EDT  –  1 Ceres at opposition
31 Jan 2018, 11:28 EST  –  1 Ceres at opposition
22 Apr 2018, 09:39 EDT  –  1 Ceres at perihelion
28 May 2019, 21:27 EDT  –  1 Ceres at opposition

Image credit

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




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