Jupiter at opposition
2017 Apr 7
Dominic Ford – originally published on In-The-Sky.org
From London (click to change), it will be visible between 20:25 and 05:46. It will become accessible at around 20:25, when it rises 7° above your eastern horizon, and then reach its highest point in the sky at 01:07, 32° above your southern horizon. It will become inaccessible at around 05:46 when it sinks to 7° above your western horizon.
Jupiter in coming weeks
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 position of Jupiter at the moment it passes opposition will be:
|Object||Right Ascension||Declination||Constellation||Magnitude||Angular Size|
The coordinates above are given in J2000.0.
The geometry of the solar system
This optimal positioning occurs when Jupiter 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 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 the Sun in the sky, the solar system is lined up so that Jupiter, the Earth and the Sun form a straight line with the Earth in the middle, on the same side of the Sun as Jupiter.
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.
On this occasion, Jupiter will lie at a distance of 4.46 AU, and its disk will measure 43.3 arcsec in diameter, shining at magnitude -2.5. Even at its closest approach to the Earth, however, 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.
The details of this observing event were provided courtesy of In-The-Sky.org