© 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 Seattle, it will be visible between 20:27 and 06:05. It will become accessible around 20:27, when it rises to an altitude of 7° above your eastern horizon. It will reach its highest point in the sky at 01:16, 37° above your southern horizon. It will become inaccessible around 06:05 when it sinks below 7° above your western horizon.

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2014 apparition of Mars

01 Mar 2014 – Mars enters retrograde motion
08 Apr 2014 – Mars at opposition
14 Apr 2014 – Mars at perigee
19 May 2014 – 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 2014, 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 2014 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
11 Feb 2014
Mars
11 Mar 2014
Mars
08 Apr 2014
Mars
06 May 2014
Mars
03 Jun 2014

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

Date Angular size Mag
28 Jan 20148.6”0.3
11 Feb 20149.8”-0.0
25 Feb 201411.2”-0.4
11 Mar 201412.8”-0.8
25 Mar 201414.2”-1.2
08 Apr 201415.1”-1.5
22 Apr 201415.0”-1.3
06 May 201414.1”-1.0
20 May 201412.8”-0.7
03 Jun 201411.5”-0.4
17 Jun 201410.4”-0.2

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 2014 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 0.62 AU, and its disk will measure 15.1 arcsec in diameter, shining at magnitude -1.5. Its celestial coordinates at the moment it passes opposition will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Mars 13h12m50s 5°03'S Virgo -1.5 15.1"

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 08 April 2014
Sunrise
06:32
Sunset
19:52
Twilight ends
21:40
Twilight begins
04:44

9-day old moon
Waxing Gibbous

68%

9 days old

Planets
Rise Culm. Set
Mercury 06:17 12:14 18:12
Venus 05:02 10:20 15:38
Moon 13:24 20:41 03:48
Mars 19:35 01:16 06:57
Jupiter 10:58 18:54 02:51
Saturn 22:33 03:24 08:15
All times shown in PDT.

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

08 Apr 2014  –  Mars at opposition
14 Apr 2014  –  Mars at perigee
22 May 2016  –  Mars at opposition
30 May 2016  –  Mars at perigee

Image credit

© NASA/Hubble Space Telescope

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