Dominic Ford, Editor
From the Outer Planets feed
From Cambridge, it will be visible between 21:33 and 04:15. It will become accessible around 21:33, when it rises to an altitude of 7° above your south-eastern horizon. It will reach its highest point in the sky at 00:56, 22° above your southern horizon. It will become inaccessible around 04:15 when it sinks below 8° above your south-western horizon.
Mars opposite the Sun
This optimal positioning occurs when Mars 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 Mars 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 Mars lies opposite the Sun in the sky, the solar system is lined up so that Mars, the Earth and the Sun form a straight line with the Earth in the middle, on the same side of the Sun as Mars.
The time of Mars's perigee is an especially good time to observe it, since it neighbors the Earth in the solar system and has the greatest variation of all of the planets in its distance from the Earth. This in turn leads to a large variation in its apparent size and brightness.
When it passes opposition, Mars glides past the Earth rather quickly, and so only appears large and bright in the sky for a few weeks. A graph of the angular size of Mars at this opposition is available here, and a graph of its brightness is available here.
On this occasion, Mars will lie at a distance of 0.39 AU, and its disk will measure 24.3 arcsec in diameter, shining at magnitude -2.8. 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 without the aid of a telescope.
Mars in coming weeks
Over the weeks following its opposition, Mars 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 Mars 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 sky on 27 July 2018|
14 days old
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.
|27 Jul 2018||– Mars at opposition|
|13 Oct 2020||– Mars at opposition|
|08 Dec 2022||– Mars at opposition|
|15 Jan 2025||– Mars at opposition|
© NASA/Hubble Space Telescope