A Gathering of Wanderers
19 06 05
Some of the planets are currently playing a trick on us. This prestidigitation involves neither smoke nor mirrors, but like any good trick it does take advantage of illusion.
In the western skies this week, just after sunset, there will be three planets appearing to group together for a family portrait. It will end up being a tight shot, to be sure. Then after the weekend they will seem to go their separate ways. But are they really that close, nearly bumping?
It is this wandering characteristic that got the planets their name in the first place. Thousands of years ago the ancients noticed that the stars in the heavens were fixed, they didn’t move about. They predictably showed up in the same heavenly real estate year after reliable year.
But there were some stars that seemed to “travel.” Throughout the year anyone who kept an eye on them saw that they sort of… well, really wandered through the sky. So they were given the name “planets” from the greek work “planetes,” which means, to no one’s surprise, wanderer.
Of course we now know that the planets are not stars, but small rocky and gassy bodies orbiting the sun. They are not the incredibly distant actual stars that are so far away that most don’t appear to move at all in a person’s entire lifetime.
And since all the planets move on essentially the same plane, there are going to be times when they appear to get real close to each other.
Such is what is happening this week as Venus, Mercury, and Saturn group together for a nice portrait after sunset. But the grouping is just an illusion; they will be nowhere near each other. Let me tell you how they pull it off.
We are in the part of our orbit where we have passed distant Saturn months ago in our run around the sun, but are now being chased by Mercury and Venus on their inside tracks.
Imagine racing around a track with all runners in staying in their own lanes. Imagine looking back as you run around the turn, seeing a distant runner that you have already passed but, at the same time, spotting two runners who are fast catching up with you on the inside lanes.
Imagine looking over your shoulder at the precise moment when it appears that they – the runner you have passed and the two catching up – are coincidentally in the same line of sight. They appear to be grouped, but are actually nowhere near each other.
That’s what we’ll be seeing all this week about 45 minutes after sunset. We are actually looking back and seeing Mercury and Venus rounding the sun and ready to move by us, as poor distant Saturn lags way, way behind.
But it appears they are all gathering in one spot in the sky.
You can start watching this evening. Venus will be the brightest dot in the twilight skies. A good eye will pick out dim Mercury to its lower right at less than three degrees away. Saturn is a brighter dot on the opposite side of Venus and slightly farther.
Go outside about the same time in the next few days and see for yourself how it appears that Mercury is approaching Venus from below, Saturn from above. They are all “wandering” as they did for the ancients for thousands and thousands of years.
It all comes to a climax over this coming weekend when, over successive nights, the three - now so close they are called a “trio” in astronomy parlance - get together in the closest trio since the last century. The only thing missing from this sky scene is a beautiful crescent Moon as a backdrop.
Mind you, Saturn is actually 800 million miles farther away than our two inner neighbors, who themselves are more than 40 million miles apart. Remember their “grouping” is just part of the illusion.
After the weekend they will begin to part ways again. These get-togethers never last.
If you get a chance to see it, do. There will be another trio next year, but its proximity to the sun will make it very difficult to appreciate. After that you’ll be waiting decades for another great grouping of these wandering magicians.