If you are an early riser, you will have noticed that four of the five naked-eye planets are visible in a great arc from the southeastern to the southwestern sky. For the next couple of weeks, elusive Mercury joins the tableau. You’ll be able to see all the planets visible to humans until the discovery of Uranus just 235 years ago.
Start about an hour before sunrise. You’ll need a southern horizon clear of trees and buildings. You are looking for an arc of bright objects starting in the SSW rising to the south and sinking again to the southeast.
It also helps to have a sky map. You’ll find a good one at http://earthsky.org/science-wire/when-will-all-five-visible-planets-appear-simultaneously.
Look SSW for bright Jupiter, the fifth planet from the sun. Pretty far to the left of Jupiter to the WSW is the star Spica. Almost directly south and near the top of the arc is dim, reddish Mars.
Down and to the left of Mars along the arc is yellowish Saturn. Don’t confuse it with the star Antares, which is down and to the right of Saturn.
Down and to the left of Saturn and almost directly southeast is blazingly white Venus. Down and to the left of Venus and very low on the horizon is difficult-to-see Mercury.
Seeing the five naked-eye planets over the course of a night is commonplace to those of us who have spent a few thousand nights outdoors. Seeing all eight of the major planets is more difficult. In fact, in my misspent youth I spent a few nights doing “planet marathons,” when I saw all of the nine planets, Pluto included, over a single night. Just for fun, we threw in a few bright asteroids – what are now called dwarf planets – like Ceres and Vesta.
Invariably, some were setting in the evening or rising in the morning just before the sun rose. The planets are visible most of the time. Each one spends a bit of time too close to the sun too see, but they are mostly visible if you know when and where to look and you’re willing to lose a night’s sleep.
Go beyond the naked-eye five, and you’ll need some help. Uranus will take binoculars, and Neptune and the asteroids require a telescope. Pluto requires a big telescope and a detailed star map to distinguish it from the plethora of stars that look exactly like it.
The “fabulous five” are easy enough for any beginner. You can see them with the binoculars you were born with, but binoculars might help you when trying to spot Mercury. Again, you might have to stay up all night to see them most of the time.
Their appearance at the same moment is more unusual. The last time it happened was at the end of 2004 and briefly into 2005. If you don’t like dragging yourself out of bed before the sun rises, take heart. By August, all of the original five will have migrated to the evening sky, so you’ll get another opportunity.
The problem child here is Mercury. The closest planet to the sun never gets very far from it from our point of view. It reaches its greatest elongation – when it appears farthest from the sun in the sky – during the first week of February. After that, it will dive closer to the sun, and your chances of seeing it diminish with each passing day. What with central-Ohio clouds and all, I’ve seen the most elusive of naked-eye planets only a dozen or so times. If you see it, you will become one of the elite few who have done so throughout the course of human history. Take the opportunity to do so while you have bright Venus to point the way.
There’s another reason to give it a go this time around. Note how the planets seem to mark an arc across the southern sky. The arc is part of a great sky circle called the ecliptic, the path the sun appears to take as it makes its yearly trek around the sky.
What it really marks is the plane Earth travels as it orbits the sun. The other major planets travel in orbits that are pretty close to that plane. Thus, their positions are pretty close to the ecliptic. Connect the planetary dots and you’ll see the ecliptic, not on some star map but with your own two eyes.
But you are also seeing something more. Astronomers say with a high degree of certainty that the planets formed from a spinning, flattened disk of dust and gas.
How can they be so certain? Well, there it is. They all move slowly around the sky in the same direction, and they all move more or less along the plane of the original flattened disk. There really is no better explanation, and you can see so for yourself and not have to take some blessed astronomer’s word for it.
Go out. Look. Be the seeker after truth that you may secretly know in your heart of hearts you were born to be.
Tom Burns is director of the Perkins Observatory in Delaware.