Mars's orbit around the Sun will carry it to its closest point to the Earth – its perigee – passing within 0.38 AU of us.
Since the size and brightness of Mars in the night sky both increase when it is close to us, the days around its perigee represent the best time to observe it.
This effect is especially pronounced for Mars since it neighbours the Earth in the Solar System, orbiting a little further out from the Sun than us, at an average distance of 1.52 AU. As a result, it has the greatest variation of all the planets in its distance from the Earth, depending on whether the two planets are on opposite sides of the Sun, or passing next to one another in their respective orbits.
Mars reaches perigee at around the time when it passes the Earth in its orbit. At this time, the Sun, Earth and Mars lie in a straight line, with the Earth in the middle.
Consequently, Mars appears almost exactly opposite the Sun in the sky – a configuration called opposition, when Mars reaches its highest point in the sky at midnight and is visible for much of the night.
Every perigee of Mars is associated with a near-simultaneous opposition, but the two events typically occur a few days apart owing to the significant ellipticity of Mars's orbit.
On this occasion, Mars will attain a maximum angular diameter of 24.3 arcsec at closest approach, and a maximum brightness of magnitude -2.8 .
Observing Mars
Even at its closest approach to the Earth, it is never possible to distinguish Mars as more than a star-like point of light with the naked eye, though a simple pair of binoculars is sufficient to reveal it as a disk of light.
From Cambridge , it will be visible between 21:19 and 03:53. It will become accessible at around 21:19, when it rises to an altitude of 7° above your south-eastern horizon. It will reach its highest point in the sky at 00:36, 21° above your southern horizon. It will become inaccessible at around 03:53 when it sinks below 7° above your south-western horizon.
A chart of the path of Mars across the sky in 2018 can be found here, and a chart of its rising and setting times here.
The position of Mars at the moment it passes perigee will be:
| Object | Right Ascension | Declination | Constellation | Magnitude | Angular Size |
| Mars | 20h26m50s | 25°54'S | Capricornus | -2.8 | 24.3" |
The coordinates above are given in J2000.0.
The sky on 31 Jul 2018
| The sky on 31 July 2018 | ||||||||||||||||||||||||||||||||||
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86% 18 days old |
All times shown in EDT.
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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
| 31 Jul 2018 | – Mars at perigee |
| 27 Aug 2018 | – Mars ends retrograde motion |
| 23 Aug 2020 | – Mars 2020: a great chance to see the red planet |
| 09 Sep 2020 | – Mars enters retrograde motion |
Image credit
© NASA/Hubble Space Telescope