© NASA/Cassini

Jupiter at opposition

Dominic Ford, Editor
From the Outer Planets feed

Objects: Jupiter
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The sky at

Jupiter will reach opposition, when it lies opposite to the Sun in the sky. Lying in the constellation Aries, it will be visible for much of the night, reaching its highest point in the sky around midnight local time.

From Seattle, it will be visible between 18:57 and 07:05. It will become accessible around 18:57, when it rises to an altitude of 8° above your eastern horizon. It will reach its highest point in the sky at 01:01, 54° above your southern horizon. It will become inaccessible around 07:05 when it sinks below 7° above your western horizon.

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2011 apparition of Jupiter

30 Aug 2011 – Jupiter enters retrograde motion
28 Oct 2011 – Jupiter at opposition
25 Dec 2011 – Jupiter ends retrograde motion

A close approach to the Earth

At around the same time that Jupiter 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 Jupiter lies opposite to the Sun in the sky, the Earth passes between Jupiter and the Sun. The solar system is lined up with Jupiter 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.

The panels below show a comparison of the apparent size of Jupiter when seen at opposition in 2011, and when it is most distant from the Earth at solar conjunction.

Jupiter
Jupiter at 2011 opposition
Jupiter
Jupiter at solar conjunction

A comparison of the size of Jupiter as seen at 2011 opposition and at solar conjunction.

In practice, however, Jupiter orbits much further out in the solar system than the Earth – at an average distance from the Sun of 5.20 times that of the Earth, and so its angular size does not vary much as it cycles between opposition and solar conjunction.

Observing Jupiter

At opposition, Jupiter 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, it is not possible to distinguish it as more than a star-like point of light with the naked eye, though a good pair of binoculars is sufficient to reveal it as a disk of light with accompanying system of moons.

A chart of the path of Jupiter across the sky in 2011 can be found here, and a chart of its rising and setting times here.

At the moment of opposition, Jupiter will lie at a distance of 3.97 AU, and its disk will measure 48.6 arcsec in diameter, shining at magnitude -2.9. Its celestial coordinates at the moment it passes opposition will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Jupiter 02h13m20s 11°49'N Aries -2.9 48.6"

The coordinates above are given in J2000.0.

Over the weeks following its opposition, Jupiter 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 September 2021
Sunrise
06:48
Sunset
19:20
Twilight ends
21:04
Twilight begins
05:04

10-day old moon
Waxing Gibbous

92%

10 days old

Planets
Rise Culm. Set
Mercury 09:23 14:37 19:51
Venus 10:47 15:41 20:35
Moon 18:29 23:05 03:50
Mars 07:24 13:28 19:32
Jupiter 18:12 23:08 04:05
Saturn 17:26 21:59 02:33
All times shown in PDT.

Source

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

28 Oct 2011  –  Jupiter at opposition
02 Dec 2012  –  Jupiter at opposition
05 Jan 2014  –  Jupiter at opposition
06 Feb 2015  –  Jupiter at opposition

Image credit

© NASA/Cassini

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