© NASA/Hubble Space Telescope

Mars ends retrograde motion

Dominic Ford, Editor
From the Outer Planets feed

Objects: Mars
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Mars will reach the end of its retrograde motion, ending its westward movement through the constellations and returning to more usual eastward motion instead. This reversal of direction is a phenomenon that all the solar system's outer planets periodically undergo, a few months after they pass opposition.

The retrograde motion is caused by the Earth's own motion around the Sun. As the Earth circles the Sun, our perspective changes, and this causes the apparent positions of objects to move from side-to-side in the sky with a one-year period. This nodding motion is super-imposed on the planet's long-term eastward motion through the constellations.

The diagram below illustrates this. The grey dashed arrow shows the Earth's sight-line to the planet, and the diagram on the right shows the planet's apparently movement across the sky as seen from the Earth:


The retrograde motion of a planet in the outer solar system. Not drawn to scale.

2020 apparition of Mars

09 Sep 2020 – Mars enters retrograde motion
06 Oct 2020 – Mars at perigee
13 Oct 2020 – Mars at opposition
13 Nov 2020 – Mars ends retrograde motion

Observing Mars

Mars leaves retrograde motion as its 2020 apparition comes to an end, although it will remain visible for some weeks in the dusk sky.

Its celestial coordinates as it leaves retrograde motion will be:

Object Right Ascension Declination Constellation Magnitude Angular Size
Mars 00h56m20s +05°03' Pisces -1.7 17.7"

The coordinates above are given in J2000.0.

From Fairfield , it will be visible in the evening sky, becoming accessible around 16:57 (EDT) as the dusk sky fades, 21° above your eastern horizon. It will then reach its highest point in the sky at 21:15, 53° above your southern horizon. It will continue to be observable until around 02:50, when it sinks below 8° above your 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.

Over the following weeks, Mars will reach its highest point in the sky four minutes earlier each night, gradually disappearing into evening twilight.

The panels below show the month-by-month change in Mars' apparent size in coming weeks, as it recedes from the Earth:

Mars
18 Sep 2020
Mars
16 Oct 2020
Mars
13 Nov 2020
Mars
11 Dec 2020
Mars
08 Jan 2021

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

Date Angular size Mag
04 Sep 202019.5”-1.9
18 Sep 202021.4”-2.2
02 Oct 202022.5”-2.5
16 Oct 202022.1”-2.6
30 Oct 202020.2”-2.2
13 Nov 202017.7”-1.7
27 Nov 202015.1”-1.2
11 Dec 202012.9”-0.8
25 Dec 202011.1”-0.4
08 Jan 20219.6”-0.0
22 Jan 20218.5”0.3
The sky on 13 November 2020
Sunrise
06:37
Sunset
16:37
Twilight ends
18:13
Twilight begins
05:05

28-day old moon
Waning Crescent

2%

28 days old

Planets
Rise Culm. Set
Mercury 04:58 10:25 15:52
Venus 03:52 09:34 15:16
Moon 04:21 10:15 15:57
Mars 14:54 21:15 03:35
Jupiter 11:17 15:58 20:39
Saturn 11:31 16:16 21:00
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

13 Nov 2020  –  Mars ends retrograde motion
12 Jul 2021  –  Mars at aphelion
20 Sep 2021  –  Mars at apogee
07 Oct 2021  –  Mars at solar conjunction

Image credit

© NASA/Hubble Space Telescope

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