Star Trak: March 2018

BLOOMINGTON, Ind. -- Venus and Mercury will appear so close that they will be in the same binocular field of view for the first three weeks of March. Venus will be much brighter and easy to spot 5 degrees above the western horizon a half hour after sunset. Mercury will be nearby, less than 2 degrees to the lower right (north) and about 10 times dimmer. Both planets will set less than an hour after the sun.

Mercury in its smaller orbit moves faster than Venus, and it will pass 1.1 degrees north of the brighter planet on March 3. Mercury will reach its peak on March 15, standing 12 degrees high in the west 30 minutes after sunset. After mid-month it will drop back toward the horizon, passing Venus again in the opposite direction on March 17. Soon after that Mercury will be too faint to see with the unaided eye in the bright glow of twilight. It will pass between Earth and the sun on April 1.

Jupiter will rise in the east shortly before midnight at the start of March and an hour earlier by month's end. It will grow larger and brighter as the month advances.

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Zodiacal light seen from Paramal Observatory in Chile. NASA

Mars and Saturn will rise about 70 minutes apart at the beginning of the month but only about one minute apart by month's end. Mars will come up about 2 a.m. local time at the start of March and be at its highest in the south around sunrise. It will not yet be large enough to show details of the surface in most telescopes.

Saturn will be conspicuous in the southeast all month, its golden color a striking contrast to the red-orange of Mars. Saturn's rings will be tilted 26 degrees to our line of sight, and its largest moon, the planet-sized Titan, can be seen with any telescope.


The sun will cross the celestial equator (an extension of Earth's equator onto the sky) at 12:15 p.m. EDT (16:15 Universal Time) March 20 heading north. This will mark the start of spring in the Northern Hemisphere and autumn in the Southern Hemisphere. For the next six months in the Northern Hemisphere, the days will be longer than the nights.

Day and night are not precisely the same length at the time of the equinox. That happens on different dates for different latitudes. At higher latitudes in the Northern Hemisphere, the date of equal day and night occurs before the March equinox. In the Southern Hemisphere, this happens after the March equinox. Information about the exact time of the equinox at different places on Earth's surface is provided by the U.S. Naval Observatory.

Zodiacal light

If you live in an area that is dark enough for you to see the Milky Way sprawling across the night sky, you also have a chance of seeing the interplanetary dust in the plane of our solar system. Moonless evenings in late winter and early spring are the best time to see this dust.

As darkness falls, look for a faint pyramid of light spreading upward from the western horizon over a large area of the sky. This is the zodiacal light, which is sunlight reflected from trillions of dust particles left behind in space by comets and asteroids that orbit the sun in the same plane as the planets. Observers at mid-northern latitudes may be able to see the zodiacal light after evening twilight ends between March 3 and 18, when the moon will be out of the sky.

Moon phases

The moon will be full on March 1, at third quarter on March 9, new on March 17, at first quarter on March 24 and full again on March 31.

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