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136199 Eris at opposition

Dominic Ford, Editor
From the Dwarf Planets feed

Objects: 136199 Eris
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The sky at

136199 Eris will be well placed in the sky, in the constellation Cetus. It will be visible for much of the night, reaching its highest point in the sky around midnight local time.

From Cambridge, it will be visible between 20:55 and 04:36. It will become accessible around 20:55, when it rises to an altitude of 21° above your south-eastern horizon. It will reach its highest point in the sky at 00:47, 45° above your southern horizon. It will become inaccessible around 04:36 when it sinks below 21° above your south-western horizon.

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136199 Eris opposite the Sun

This optimal positioning occurs when 136199 Eris is almost directly opposite the Sun in the sky. 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 136199 Eris passes opposition, it also makes its closest approach to the Earth – termed its perigee – making it appear at its brightest and largest.

This happens because when 136199 Eris lies opposite the Sun in the sky, the solar system is lined up so that 136199 Eris, the Earth and the Sun form a straight line with the Earth in the middle, on the same side of the Sun as 136199 Eris.

In practice, however, 136199 Eris orbits much further out in the solar system than the Earth – at an average distance from the Sun of 67.83 times that of the Earth, and so its angular size does not vary much as it cycles between opposition and solar conjunction.

On this occasion, 136199 Eris will lie at a distance of 95.12 AU, and reach a peak brightness of magnitude 18.7. Even at its closest approach to the Earth, however, 136199 Eris is so distant from the Earth that it is not possible to distinguish it as more than a star-like point of light.

136199 Eris in coming weeks

Over the weeks following its opposition, 136199 Eris will reach its highest point in the sky four minutes earlier each night, gradually receding from the pre-dawn morning sky while remaining visible in the evening sky for a few months.

A chart of the path of 136199 Eris across the sky in 2018 can be found here, and a chart of its rising and setting times here.

The position of 136199 Eris at the moment it passes opposition will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
136199 Eris 01h44m50s -02°07' Cetus 18.7 0.0"

The coordinates above are given in J2000.0.

The sky on 17 October 2018
Twilight ends
Twilight begins

8-day old moon
Waxing Gibbous


8 days old

Rise Culm. Set
Mercury 08:34 13:34 18:35
Venus 08:31 13:12 17:53
Moon 14:50 19:40 00:30
Mars 15:19 20:06 00:55
Jupiter 09:39 14:32 19:25
Saturn 12:42 17:16 21:49
All times shown in EDT.


The circumstances of this event were computed using the DE405 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).

This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location.

Related news

17 Oct 2018  –  136199 Eris at opposition
13 Apr 2019  –  136199 Eris at solar conjunction
17 Oct 2019  –  136199 Eris at opposition
13 Apr 2020  –  136199 Eris at solar conjunction

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