© NASA/Hubble Space Telescope

Mars at opposition

Dominic Ford, Editor
From the Outer Planets feed

Objects: Mars
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The sky at

Mars will reach opposition, when it lies opposite to the Sun in the sky. Lying in the constellation Virgo, 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 19:48 and 06:00. It will become accessible at around 19:48, when it rises to an altitude of 7° above your eastern horizon. It will reach its highest point in the sky at 00:54, 45° above your southern horizon. It will become inaccessible at around 06:00 when it sinks below 7° above your western horizon.

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2140 apparition of Mars

26 Feb 2140 – Mars enters retrograde motion
05 Apr 2140 – Mars at opposition
10 Apr 2140 – Mars at perigee
16 May 2140 – 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 2140, 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 2140 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
09 Feb 2140
Mars
08 Mar 2140
Mars
05 Apr 2140
Mars
03 May 2140
Mars
31 May 2140

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

Date Angular size Mag
26 Jan 21408.5”0.3
09 Feb 21409.7”0.0
23 Feb 214011.1”-0.4
08 Mar 214012.6”-0.8
22 Mar 214014.0”-1.1
05 Apr 214014.8”-1.4
19 Apr 214014.7”-1.3
03 May 214013.8”-1.0
17 May 214012.5”-0.7
31 May 214011.3”-0.4
14 Jun 214010.1”-0.1

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 2140 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 0.63 AU, and its disk will measure 14.8 arcsec in diameter, shining at magnitude -1.4. Its celestial coordinates at the moment it passes opposition will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Mars 12h56m50s 3°09'S Virgo -1.4 14.8"

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 25 Nov 2024

The sky on 25 November 2024
Sunrise
06:50
Sunset
16:26
Twilight ends
18:04
Twilight begins
05:13

24-day old moon
Waning Crescent

20%

24 days old

Planets
Rise Culm. Set
Mercury 08:30 12:58 17:26
Venus 10:15 14:43 19:11
Moon 01:23 07:34 13:35
Mars 20:42 04:05 11:28
Jupiter 17:13 00:40 08:07
Saturn 12:57 18:29 00:01
All times shown in EST.

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

05 Apr 2140  –  Mars at opposition
10 Apr 2140  –  Mars at perigee
16 May 2140  –  Mars ends retrograde motion
12 Apr 2142  –  Mars enters retrograde motion

Image credit

© NASA/Hubble Space Telescope

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