Jupiter, king of planets, has been our constant evening companion for the past six months. But March marks the end of Jupiter’s reign over our evening sky.

Jupiter goes out with a flourish, with a lovely conjunction between Jupiter and the planet Mercury in mid-March.

At the start of March, look for Jupiter around 7:30 a.m. low in the west. Jupiter shines at minus 2 magnitude, by far the brightest dot in the evening sky. Around dusk at the start of the month, Jupiter is about 15 degrees above the west horizon. You can use your hand as a measuring device. Your fist at arm’s length is about 10 degrees in diameter; so Jupiter is about 1.5 fists above the western horizon at 7:15 p.m. On March 1, Jupiter sets about 8:30 p.m.

In early March, Jupiter will be a little lower at dusk. By March 10, Jupiter is only 10 degrees above the horizon at 7:15 p.m. (one fist) and sets by 8 p.m.

Look for the early crescent just to the right of Jupiter on March 6.

By March 10, you may be able to see the planet Mercury down below Jupiter. On that night Mercury will very low at dusk, only about 4 degrees above the west horizon. That’s about the width of two fingers held at arm’s length. You’ll need a perfectly flat horizon, with no hills, trees, buildings (or clouds) in your way to see Mercury. Mercury does shine much more brightly than usual, at minus 1.23 magnitude; so if you have that clear horizon, you should be able to see this elusive planet.

From March 10 to 15, Mercury appears a little higher each night at dusk, while Jupiter appears a little lower.

By March 15, the two planets will be side by side, low in the west at 7:15 p.m. Jupiter will be the brighter one, on the left; Mercury will be on the right and shines that night at minus 0.9. The two planets will appear only two degrees apart from each other. At 7:15 p.m., the planets will be about seven degrees (a little more than three fingers) above the horizon. Mercury and Jupiter will set simultaneously at 7:45 p.m. on March 15.

In the third week of March, Jupiter will be a little lower in the sky each night at dusk. By March 25, Jupiter will be lost in the light of the setting sun, and its long-running appearance in our evening skies will be over. Roughly a month later, in late April, Jupiter will reappear in the morning sky, heading for a beautiful gathering with Venus in the morning skies in early May.

MERCURY FORGES ON

Mercury will remain in the evening sky for the rest of the month. From March 15 to 25, Mercury will be roughly 10 degrees above the horizon in the west and will set around 8 p.m. With Jupiter gone, Mercury will be the most obvious dot of light in the sky at dusk in the third week of March. On March 22, it reaches its greatest apparent distance from the sun.

By the end of the month, Mercury is back to being only a few degrees above the horizon at dusk, and sets by 7:45 p.m. The planet’s brightness also takes a plunge.

Planets appear to move against the background of the fixed stars. The closer a planet is to the sun, the faster it moves. Of all planets, Mercury moves the fastest, since it is the planet closest to the sun. Perhaps due to its fast motion, Mercury was depicted in Greek mythology as the speedy, winged-footed messenger of Jupiter and the other gods.

NASA’s current mission to Mercury is also called Messenger. This March, as Mercury shines in our dusk skies, the Messenger spacecraft will go into orbit around the planet. Messenger has made three fly-bys of the planet already. If you visit Science on a Sphere in the planetarium lobby at Bishop Museum, you can bring up some of its images on that vivid 6-foot sphere yourself.

SATURN JOINS EVENING SKY

Although Jupiter is leaving the evening sky, Saturn has become an evening planet. Look for Saturn rising almost due east at 9 p.m. at the start of March; in early March, Saturn is halfway up in the east by midnight and halfway down in the western sky as day breaks. The planet shines at 0.4 magnitude. By the end of March, Saturn rises at sunset, is high overhead at midnight and sets at dawn.

VENUS BLAZES ON

Venus remains the queen of the morning sky, though it’s now much lower at dawn than it was earlier this year. Venus rises in the east around 4:30 a.m. throughout March. Venus remains brilliant at minus 4 magnitude. The month begins and ends with the lovely sight of a crescent moon next to Venus.

THE MARCH SKY MAP

The map for March is good for 9 p.m. at the start of March, 8 p.m. in the middle of the month, and 7 p.m. at the end of the month. As always, hold this map over your head.

Look for the Big Dipper low in the northeast.

In the south, looks for the star Canopus, the second-brightest in the sky. It’s also a good example of a star we can see from Hawaii, but which never rises above the horizon in most of the continental U.S.

Look for Orion the Hunter high in the southwest, with its familiar hourglass shape, distinctive belt of three stars, and brilliant stars Rigel and Betelgeuse.

The belt of Orion points up to Aldebaran, the bright star in Taurus the Bull. Take the belt of Orion the other way to find Sirius, in Canis Major (Big Dog), the brightest star in the sky.