Four planets tangle

Mercury, Mars, Saturn, and Neptune move into a grouping that will be most concentrated on April 13. But they are only about 20° west of the Sun and out from it at a low angle to the horizon, as seen from northern latitudes.

Still, it’s worth contemplating the pre-dawn scene and comparing it with our picture for April 8, repeated here to make the comparing easier.

The earlier picture was for a deeper stage of twilight so as to show comet 2025 R3 PANSTARRS coming into view over the  horizon. The April 13 view has to be only shortly before sunrise so as to show the four planets at all.

The arrow through the comet shows its motion from 2 days earlier to 2 days later. Its rush along the inner curve of its orbit is bringing it like a dart into the torso, that is, the Great Square of  the upside-down flying horse Pegasus. This comet (about which there is more on pages 31 and 128-130 of Astronomical Calendar 2026) seems to be doing better than was predicted, and may already be discernible for the unaided eye.

The gathering of planets happens to be in the direction of the vernal equinox point, the crossing of ecliptic and celestial equator. Mars crosses the equator on April 12, to be in the northern half of the celestial sphere until 2027 July 16. On April 13, Mars passes half a degree north of Neptune, and Mars, Saturn, and Neptune form a “trio,” getting to be within a circle whose diameter becomes smaller than 5°.

This space view shows the paths of the planets in April, and sightlines from Earth to them at April 13. The viewpoint is 6 AU (astronomical units, Sun-Earth distances) from the Sun at latitude 15° north of the ecliptic and longitude 185°.

There are so many ways of looking at these complexes of bodies moving relative to each other in space. In the Zodiac Wavy Chart, the swarm of planets swims into view at longitude zero on the right.

And the “Elongation” graph on page 139 of the Astronomical Calendar has another way of showing how the moving bodies cross each other’s courses in this month.

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