Trios, if you count Pluto

Peering to the right of the Sun – that is, being out on the morning side of our spinning planet – is still the way to see planetary activity.


We see Mercury hovering in the foreground; beyond it, Venus speeding in its fall toward the far side of the Sun. In the extreme background is Pluto; and in the extreme foreground the Moon comes past – the Moon in its Old stage, becoming an ever more slender C.

The result is a bunch of conjunctions: Venus-Pluto Feb. 6, 0h Universal Time (which in eastern America is 7 PM on Feb. 5); Moon-Pluto Feb. 6, 6h; Moon-Venus Feb. 6, 7h; Moon-Mercury Feb. 6, 16h.

And two “trios,” in which three of these four bodies find themselves within 5-degree-wide circles: Mercury-Venus-Pluto, most concentrated at Feb. 5, 23h; and Moon-Venus-Pluto, tightest at Feb. 6, 7h.

But those are only trios, and only of any kind of interest, if you count Pluto, which you can’t see! Whether to “count” Pluto, in this and other context, may forever remain a sore point.


There’s more likelihood of being able to see the Moon if you’re out before dawn tomorrow, Feb. 5, when it will be more than 3 days before New. The next morning, when it is down among those planets, it will have little more than 50 hours of “life” left and will be that much slimmer and harder to see.


11 thoughts on “Trios, if you count Pluto”

  1. I’ve started thinking of Pluto as the standard-bearer for the Kuiper belt, and Ceres as the matriarch of the asteroid belt. They each remind us that there are many more little bodies in our solar system in addition to the major planets. Perhaps I should add Halley’s comet on behalf of all the other comets.

    But, speaking of major planets, they certainly have been lovely on clear mornings recently, as has our little sister planet, the Moon.

    1. An idea worth capturing: Pluto, Ceres, and Comet Halley as the single members of their classes so outstanding, for varied reasons of size, distance, conspicuousness and discovery date that their status between their classes and the next classes “up” has been debatable: Pluto between dwarf planet and major planet (or between Kuiper-belt object and dwarf planet), Ceres between asteroid and dwarf planet, Halley between short- and long-period comet. Jupier may approach the ceiling between planet and brown dwarf star.

      1. One of my favorite astronomical outreach tidbits is that the Sun contains 99.8% of the mass of the solar system, and Jupiter is 70% of everything else. That always makes an impression.

      2. Dwarf planet is a subclass of major planet, as intended by the person who first coined the term, New Horizons Principal Investigator Alan Stern. This is very much in concert with the use of the term “dwarf” in astronomy, where dwarf stars are still a subclass of stars (our Sun is one of them), and dwarf galaxies are still a subclass of galaxies. Ceres is not an asteroid because the term “asteroid” refers to objects too small to be squeezed into a round or nearly round shape by their own gravity. It was wrongly classed as an asteroid long before telescopes were powerful enough to resolve it into a disk, and astronomers therefore did not know it was spherical.

        Ceres is a dwarf planet in the asteroid belt, and Pluto is a dwarf planet in the Kuiper Belt. Just calling them asteroid belt objects and Kuiper Belt Objects ignores what they are, classifying them solely by where they are in spite of the fact that the two are not mutually exclusive. Pluto is both a dwarf planet and a KBO. The first tells us what it is; the second tells us where it is. The same is true for Ceres, which is both a dwarf planet and an asteroid belt object.

        1. Fine, except that the term “asteroid” was invented for Ceres and Pallas, by Herschel in 1802. Ceres continues to be called an asteroid (as well as a dwarf planet) by many, for isntance the Oxford English Dictionary, Encyclopaedia Britannica, and Wikipedia. We may have to live with overlapping classes.

        2. I think that our nomenclature tells us more about our understanding of an object than about the object itself. Thus I would rather say, for instance, “Ceres is now classified as a dwarf planet,” than “Ceres is a dwarf planet.” If the dwarf planet nomenclature remains consistent for a few decades, the concept of “dwarf planet” will become more thing-like, but for now it still seems fairly provisional. And we should always be careful not to mistake the finger pointing at the Moon for the Moon herself.

  2. …it is cloudy here in the Philippines,so only the moon ? and Venus is somewhat visible.It’s 5:30 am

    1. That’s great!
      I’ve been ad admirer of Debbie Byrd and her “Earth and Sky” ever since I met her at the Texas Star Party, of which she was the founder.

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