Almost all of the planets of our solar system are spread across our early evening sky right now. Of these, four are easily visible and worth stepping outside to take a look at. Some are calling this gathering a planetary alignment, but that appears to be giving many folks the wrong impression about what is happening.
Here’s what you should know when you go outside to see for yourself: Yes, the planets are indeed lined up across our sky. No, they are not strung out from the sun in a three-dimensional straight line extending into space, as I’ve seen depicted in graphics for this event. The truth is, that exact scenario never happens.
Yes, the planets are currently in alignment, but they always are — a fact that is too often overlooked. You will never see them any other way. Draw an imaginary line through any two planets you see, extend it across the sky and you’ll have an approximation of the orbital plane, or flat disk, of our solar system as seen from Earth. This is our edge-on view.
The planets of our solar system go around the sun in the same direction and on roughly the same plane. Picture the planets — including our own planet Earth — circling the central sun on a table top, all at different distances. Or, for those who remember vinyl records, think of the grooves around the central hub as the planets’ orbits.
Earth’s orbit lies in that same plane, so from our perspective, we cannot see the planets going around the sun. Instead, they all appear along the same two-dimensional line in our sky. Sometimes they get lost in the glare of the sun, which is also on this line. Each orbits the sun at a different speed from the rest, so they are constantly mixing it up, endlessly rearranging themselves along this “plane of the ecliptic.”
Our ancestors took note of the planet’s unruly behavior and assigned special significance to the stars through which they and the sun appeared to travel. This is where the 12 constellations, or signs, of the zodiac come from. As smart as they were, the ancients had no way of knowing just how vastly far beyond the planets the starry backdrop was.
The plane of the ecliptic — the path of the planets in our sky — surrounds Earth. If Earth was transparent, we could see all the planets that were not lost in the sun’s glare, as they are when passing around the sun’s far side. In addition to passing around the sun’s far side, the two inner planets, Venus and Mercury, pass between us and the sun. Uranus and Neptune, regardless of where they were in their orbits, would be too distant and dim to see without a telescope.
In reality, Earth leaves us with only half of the sky to see at a time, so it is noteworthy when the planets gather in the early evening sky — the part most accessible to the average person. Only Mercury is missing as it is about to round the far side of the sun.
This “line-up” is changing over time, but here’s what is visible right now: Venus is the brightest and the first to punch through the fading light of dusk in the southwest. As the night deepens, you can find the fourth and dimmest visible planet hanging a bit more than the width of your outstretched palm below brilliant Venus. This is Saturn, the farthest planet most people will ever see without a telescope.
Check Saturn out soon though. It is getting lower each evening, and will be absorbed into the glow of sunset in the coming weeks. Closer to the lower left of Venus, but hidden by its great distance, is Neptune, the eighth and outermost planet.
Turning our attention to the southeast, we find Jupiter high up, but not quite overhead. Just beneath Jupiter hangs the star Aldebaran. Tonight’s waxing gibbous moon shines to Jupiter’s right. The planet Uranus floats in the distance about as far to the moon’s lower right as Aldebaran is below Jupiter, but you’ll need binoculars to see it. Tomorrow night, the moon will pass closer above Jupiter than Aldebaran is below it.
Winter’s magnificent Orion constellation hangs below Jupiter, and Sirius, the night’s brightest star, sparkles to the lower left of Orion. To their left in the east, the distinctly reddish hue of Mars makes it stand out next to Gemini’s twin stars Castor and Pollux.
To me, Mars is the “star” of this show since it is still nearly at its brightest after reaching opposition (positioned most directly opposite the sun in our sky) last month. Quite noticeable is its reddish or orange hue, the actual color of Mars’s rusty ground reflecting the sun’s light. A sharply focused telescope on a steady mount can reveal the white polar ice caps at moderate magnifications.
To fully appreciate this vista, it is helpful to remember that we see the planets by reflected sunlight. They do not shine on their own, but are illuminated by the same sun that gives us daylight — the one at the center of our solar system.
As the evening wears on, Earth turns eastward, and the sky appears to shift westward, taking the planets along with it. By 10 p.m., Venus is settling to the west while Jupiter crosses high in the south and Mars gains height in the east. This progression continues as the moon and Jupiter set in the west after midnight, and Mars heads down before the crack of dawn.
With space probes, we’ve now explored each of the solar system’s worlds we can see with our own eyes, as well as a bunch that we cannot. It still astounds me to be able to say that I personally remember the sky as it was before even the first artificial satellite (Sputnik) orbited Earth, never mind probes visiting distant worlds.
Find rise and set times for the sun and moon, and follow ever-changing celestial highlights in the Skywatch section of the Weather Almanac in The Republican and Sunday Republican.
Patrick Rowan has written Skywatch for The Republican since 1987 and has been a Weather Almanac contributor since the mid 1990s. A native of Long Island, Rowan graduated from Northampton High School, studied astronomy at the University of Massachusetts-Amherst in the 1970s and was a research assistant for the Five College Radio Astronomy Observatory. From 1981 to 1994, Rowan worked at the Springfield Science Museum’s Seymour Planetarium, most of that time as planetarium manager. Rowan lives in the Florence section of Northampton with his wife, Clara, and their cats, Eli and Milo.
