© NASA/Hubble Space Telescope

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 reach opposition, when it lies opposite to the Sun in the sky. Lying 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 San Diego, it will be visible between 20:43 and 05:00. It will become accessible at around 20:43, when it rises to an altitude of 21° above your eastern horizon. It will reach its highest point in the sky at 00:51, 55° above your southern horizon. It will become inaccessible at around 05:00 when it sinks below 21° above your western horizon.

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A close approach to the Earth

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.

This happens because when 136199 Eris lies opposite to the Sun in the sky, the Earth passes between 136199 Eris and the Sun. The solar system is lined up with 136199 Eris and the Earth on the same side of the Sun, as shown by the configuration labelled perigee in the diagram below:

When a planet is at opposition, the solar system is aligned such that the planet lies on the same side of the Sun as the Earth. At this time, the planet makes its perigee, or closest approach to the Earth. Not drawn to scale.

In practice, however, 136199 Eris orbits much further out in the solar system than the Earth – at an average distance from the Sun of 68.12 times that of the Earth, and so its brightness does not vary much as it cycles between opposition and solar conjunction.

Observing 136199 Eris

At opposition, 136199 Eris is visible for much of the night. When it lies opposite to the Sun in the sky, this means that it rises at around the time the Sun sets, and it sets at around the time the Sun rises. It reaches its highest point in the sky at around midnight local time.

But even when it is at its closest point to the Earth, 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, even through a telescope.

A chart of the path of 136199 Eris across the sky in 2019 can be found here, and a chart of its rising and setting times here.

At the moment of opposition, 136199 Eris will lie at a distance of 95.06 AU, and reach a peak brightness of magnitude 18.6. Its celestial coordinates at the moment it passes opposition will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
136199 Eris 01h45m20s 1°51'S Cetus 18.6 0.0"

The coordinates above are given in J2000.0.

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.

The sky on 17 Oct 2019

The sky on 17 October 2019
Twilight ends
Twilight begins

19-day old moon
Waning Gibbous


19 days old

Rise Culm. Set
Mercury 08:54 14:03 19:13
Venus 08:15 13:39 19:02
Moon 20:16 03:15 10:20
Mars 05:41 11:37 17:33
Jupiter 11:22 16:22 21:22
Saturn 13:04 18:05 23:07
All times shown in PDT.


The circumstances of this event were computed using the DE430 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 2019  –  136199 Eris at opposition
16 Oct 2020  –  136199 Eris at opposition
17 Oct 2021  –  136199 Eris at opposition
17 Oct 2022  –  136199 Eris at opposition

Image credit

© NASA/Hubble Space Telescope


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