In March, the action in the predawn sky really picks up. The month opens with Mars, Jupiter and Saturn forming a straight line, in that order from right to left, above the southeastern horizon. On the 4th, the three planets are spaced almost evenly apart.
But that neat arrangement soon gives way as the planets switch positions. Jupiter and Saturn are about to leapfrog past Mars, and all because Mars, being the closest to the sun, orbits the fastest.
What’s happening is that Earth’s orbit is carrying us eastward and thus toward all these planets, making them move higher and westward. But Mars’s own orbit carries it much more rapidly eastward against the background of stars than the orbits of Jupiter and Saturn carry those planets.
As a result, Mars resists the westward movement imposed by Earth’s orbit and appears to sail eastward toward—and past—the two giant planets. Actually, though, Mars is mostly holding its own as Jupiter and Saturn sail past it on their westward journey.
Have a look on the 18th, when Jupiter and Mars make a close pair while a crescent moon hangs right below them. The next morning, Jupiter and Mars will be closer yet and the moon will now appear below Saturn. On the 20th, Jupiter passes a mere 0.7 degrees—slightly more than a moon width—above Mars. On the 31st, the ringed planet passes about a degree above the red planet. In April the new lineup will be, from right to left, Jupiter, Saturn and Mars, with the gap between Mars and the other two planets rapidly widening.
In the evening sky, a young moon comes out below Venus on the 26th and 27th. And don’t miss the show as the brilliant planet and the Pleiades star cluster approach each other in the last week of March. Mark your calendars for April 2nd and 3rd, when Venus glides, spectacularly, in front of the Pleiades. Be sure to have binoculars handy.
March’s full moon shines the night of the 9th. It will be big and bright, though more than six hours past full when it rises that evening.
Spring arrives with the vernal equinox at 10:50 p.m. on the 19th. At that moment the sun crosses the equator into the northern sky and Earth will be lighted from pole to pole.
March 2—First Quarter Moon
The Moon is one quarter of its way through its orbit around
the Earth, which makes half the Moon illuminated and half
dark from our perspective.
March 9—Full Moon
The Moon is located on the opposite side of the Earth as the
Sun and the side we see is fully illuminated.
March 16—Last Quarter Moon
This phase occurs when the Moon is three-quarters of the
way through its orbit around the Earth.
March 24—New Moon
The Moon is located on the same side of the Earth as the Sun
and is not visible in the night sky. This is the best time of the
month to observe faint objects like galaxies and star clusters
because there is no moonlight to interfere.
Deep Sky Objects
High above our heads, the magnificent arch of the Milky Way continues to fill the sky, visible for hours each night. The wealth of the Milky Way lies not only in the sight of the band, but also what can be found all along it: open star clusters!
Locating these clusters is a fantastic way to understand the life of stars. In January, we highlighted how to find the Great Orion Nebula, or M42, a star-forming nebula. After stars form in nebulas like M42, their mutual gravitational pull draws large groups of stars together. They remain together for a short time before the movement of the stars in the cluster and close encounters with other clusters causes the cluster to spread apart. Eventually many of the stars end up isolated. Because that dispersion hasn’t happened yet, when we look at an open cluster, we can see stars of similar ages, chemical compositions, and distances from the Sun. This makes open clusters space laboratories for scientists studying interactions between stars, how different stars evolve, and how the chemistry and structure of galaxies evolve.