Planet parade

All five naked-eye planets are lined up in the morning sky, in their order outward from the Sun. This is a fairly rare situation, and it will persist for an unusually long time, throughout June and the first half of July.

See the end note about enlarging illustrations.

This arrangement of the planets can be seen in several features of Astronomical Calendar 2022, such as the solar-system plan for June:

and the “Elongation” graph, from which this is a slice:

You see Mars’s line crossing Jupiter’s at May 29, and Mercury’s crossing the Sun at July 16.

For the situation started on May 29 when Mars changed places with Jupiter – passed to the westward of it – and will end on July 16 when Mercury is at superior conjunction – passes to eastward of the Sun.

Let’s call this situation a morning parade. Someone asked when it last occurred and will next occur.

To find out, I wrote a program, which I thought would be quite short and easy, but it took me all of yesterday and the small hours of today. It’s based on finding the elongations of the planets – their angular distances east or west of the Sun – and then finding whether (for the morning sky) Mercury is west of the Sun and Venus west of Mercury and so on. Here’s a result.

2000-2050
parades of planets in the morning sky
  elong.of Mercury  Venus  Mars Jupiter Saturn
2002 Nov  4   -6.4   -7.5  -29.1  -84.7 -132.8
2002 Nov 14   -0.1  -20.4  -32.7  -94.0 -143.3
11 days
2004 Dec 11   -2.4  -26.4  -29.3  -64.5 -142.9
2004 Dec 28  -22.3  -22.5  -35.0  -79.7 -161.4
18 days
2022 May 30  -12.3  -37.0  -64.9  -65.2 -103.3
2022 Jul 16   -1.7  -26.0  -76.0 -105.0 -149.5
48 days
2041 Mar 28  -16.6  -16.8  -23.8 -158.4 -165.2
2041 Apr  4  -11.0  -24.9  -25.2 -166.1 -172.4
8 days
4 parades

Negative elongation means west of the Sun (in the morning sky). Each pair of lines is the beginning and ending dates of a parade. It appears that our current 48-day parade is the longest in this half-century. Parades can begin or end when a planet is in conjunction with the Sun, is at opposition, or passes another planet.

What about the evening sky?

2000-2050
parades of planets in the evening sky
 elong.of Mercury  Venus  Mars Jupiter Saturn
2040 Jun 23    5.5    6.3   56.0   81.6   93.4
2040 Jun 25    4.2    6.9   55.3   79.9   91.5
3 days
2040 Aug 13    1.8   20.2   38.2   40.4   48.0
2040 Aug 18    5.2   21.5   36.5   36.6   43.7
6 days
2 parades

These parades are apparently rarer. But, so far, there seems no general rule as to how often parades come about, or how long they can be. I could torment the computer by making it calculate through a century or centuries.

And it might be laboriously possible to include Uranus and Neptune (which would make parades rarer), even the Moon (making them briefer). Or to find parades of the outer planets in the opposite order, as in the late 1970s when Saturn was ahead of Jupiter, Uranus ahead of Saturn, Neptune ahead of Uranus, enabling the Grand Tour of the Pioneer and Voyager spacecraft from each to the next.

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ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format.  You may be able to enlarge them on your monitor.  One way: right-click, and choose “View image” or “Open image in new tab”, then enlarge.  Or choose “Copy image”, then put it on your desktop, then open it.  On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers).  Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.

Sometimes I make improvements or corrections to a post after publishing  it.  If you click on the title, rather than on ‘Read more’, I think you are sure to see the latest version.  Or you can click ‘Refresh’ to get the latest version.

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