When two planets lie north and south of one another on the sky’s dome, they are said to be in conjunction. Mercury will swing 3o south of Saturn on November 28, 2017. Three degrees of sky approximates the width of your thumb at an arm length from your eye. That means both of these worlds will fit inside the same binocular field of view.
Here’s how to find Mercury and Venus. Find an unobstructed horizon in the direction of sunset, and, if possible, perch yourself on a hill or balcony. Then look for Mercury and Saturn low in the western sky, near the sunset point on the horizon, starting around 45 to 60 minutes after sunset.
The Southern Hemisphere has the advantage over the Northern Hemisphere for seeing tonight’s coupling of Mercury and Saturn. South of the equator, these two worlds stay out for one and one-half hours (or more) after sunset. At mid-northern latitudes, the twosome doesn’t stay out for a lot longer than one hour after the sun.
Click here for a recommended almanac to find out the setting times for Mercury and s aturn in your sky
As one might expect, Mercury and Saturn set at nearly the same time at the equator. From the Northern Hemisphere, Mercury sets first and then Saturn sets afterwards. South of the equator, Saturn sets first and then Mercury plunges beneath the horizon. Incidentally, Mercury is the brighter of these two starlike objects, shining almost twice as brightly as Saturn. So if you only see one point of light, it’s probably Mercury.
The conjunction of Mercury and Saturn on November 28 is the first in an upcoming series of three Mercury/Saturn conjunctions. The term triple conjunction is used whenever two planets, or a planet and a star, appear due north-south of each other in the sky three different times in a relatively short space of a few months.
The second conjunction in this triple conjunction occurs on December 6, 2017, when Mercury swings less than 1.5o south of Saturn. But this conjunction will be very hard to catch because Mercury and Saturn will be buried deep in in the glare of sunset.
The third conjunction of this triple feature will the closest of them all, with Mercury sweeping about 0.7o south of Saturn on January 13, 2018. (Seven-tenths of one degree on the sky’s dome is approximately equal to the width of your little finger at an arm’s length.) This conjunction on January 13, 2018, which occurs in the morning sky, should be fairly easy to view – especially since the lit side of the waning crescent moon will be pointing right at Mercury and Saturn.
In the meantime, though, see if you can catch the evening conjunction of Mercury and Saturn after sunset on November 28, 2017.