Dominic Ford, Editor
From the Outer Planets feed
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.
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 21:15 and 03:53. It will become accessible at around 21:15, when it rises 7° above your south-eastern horizon, and then 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 to 8° above your south-western horizon.
The exact position of Mars at the moment it passes perigee will be:
|Object||Right Ascension||Declination||Constellation||Magnitude||Angular Size|
The coordinates above are given in J2000.0.
|The sky on 31 July 2018|
18 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