© NASA/Hubble Space Telescope

Mars at opposition

Dominic Ford, Editor
From the Outer Planets feed

Objects: Mars
Please wait
Loading 0/4
Click and drag to rotate
Mouse wheel to zoom in/out
Touch with mouse to dismiss
The sky at

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

From Fairfield, it will be visible between 21:43 and 04:35. It will become accessible around 21:43, when it rises to an altitude of 8° above your south-eastern horizon. It will reach its highest point in the sky at 01:09, 23° above your southern horizon. It will become inaccessible around 04:35 when it sinks below 7° above your south-western horizon.

Begin typing the name of a town near to you, and then select the town from the list of options which appear below.

2018 apparition of Mars

26 Jun 2018 – Mars enters retrograde motion
27 Jul 2018 – Mars at opposition
31 Jul 2018 – Mars at perigee
27 Aug 2018 – Mars ends retrograde motion

A close approach to the Earth

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 to the Sun in the sky, the Earth passes between Mars and the Sun. The solar system is lined up with Mars 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 Mars when seen at opposition in 2018, and when it is most distant from the Earth at solar conjunction.

Also shown is the full range of different sizes it can appear at opposition, due to the slightly oval shape of Mars' orbit. It appears largest when it reaches opposition around late August, and significantly smaller when it reaches opposition around late February.

Mars
Mars at closest opposition
Mars
Mars at 2018 opposition
Mars
Mars at furthest opposition
Mars
Mars at solar conjunction

Mars: our close neighbor

Of all the planets, Mars shows the greatest variation in its apparent size and brightness. Its angular size varies by a factor of more than seven, between 25.69" and 3.49".

This comes about because it neighbors the Earth in the solar system, orbiting the Sun at a distance of about 1.5 times the Earth's distance from the Sun. This means that its distance from the Earth varies greatly, between 0.36 AU and 2.68 AU. depending whether it lies next to, or opposite to, the Earth in its orbit.

The geometry of Mars' orbit is such that it spends much longer periods of time at large distances from the Earth than it does close to us, which provides added incentive to observe it in the weeks around opposition. Whenever it passes opposition, every two years, Mars appears large and bright for only a few weeks. The panels below show the month-by-month change in Mars' apparent size:

Mars
01 Jun 2018
Mars
29 Jun 2018
Mars
27 Jul 2018
Mars
24 Aug 2018
Mars
21 Sep 2018

The table below lists Mars' angular size at brightness at two-week intervals throughout its apparition:

Date Angular size Mag
18 May 201813.2”-0.8
01 Jun 201815.3”-1.2
15 Jun 201817.8”-1.7
29 Jun 201820.5”-2.1
13 Jul 201822.9”-2.5
27 Jul 201824.3”-2.8
10 Aug 201823.9”-2.6
24 Aug 201822.2”-2.3
07 Sep 201819.8”-1.9
21 Sep 201817.4”-1.6
05 Oct 201815.2”-1.2

This data is also available in the form of a graph of the angular size of Mars here, and a graph of its brightness here.

Observing Mars

At opposition, Mars 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 without the aid of a telescope.

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.

At the moment of opposition, 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. Its celestial coordinates at the moment it passes opposition will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Mars 20h31m30s 25°33'S Capricornus -2.8 24.3"

The coordinates above are given in J2000.0.

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 sky on 27 July 2018
Sunrise
05:43
Sunset
20:15
Twilight ends
22:11
Twilight begins
03:47

14-day old moon
Waxing Gibbous

99%

14 days old

Planets
Rise Culm. Set
Mercury 07:32 14:11 20:51
Venus 09:34 15:54 22:13
Moon 20:15 00:29 05:26
Mars 20:43 01:08 05:32
Jupiter 14:07 19:17 00:26
Saturn 18:10 22:48 03:27
All times shown in EDT.

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

27 Jul 2018  –  Mars at opposition
31 Jul 2018  –  Mars at perigee
23 Aug 2020  –  Mars 2020: a great chance to see the red planet
06 Oct 2020  –  Mars at perigee

Image credit

© NASA/Hubble Space Telescope

Share

Follow

Fairfield

Latitude:
Longitude:
Timezone:

41.14°N
73.26°W
EDT

Color scheme