Tonight – January 31, 2017 – look in a general westward direction after sunset to enjoy a close-knit couple, the moon and Venus. A fainter object, Mars, is also nearby so that these three objects, all neighbors to Earth in orbit around our sun, make a triangle on the sky’s dome. The moon and Venus will pop out into your evening twilight almost immediately after sundown. That’s because they rank as the second-brightest and third-brightest heavenly bodies, respectively, after the sun. As dusk turns into darkness, watch for the planet Mars to appear on the sky’s dome, near the waxing crescent moon and dazzling Venus.
Or, if you have binoculars, try spotting Mars near the moon and Venus before nightfall. Venus shines some 185 times more brilliantly than Mars does at present, explaining why Venus comes out first thing at dusk whereas Mars must wait until dark to make its presence known.
Venus, the second planet outward from the sun, lies inside Earth’s orbit; and Mars, the fourth planet outward, resides outside of Earth’s orbit. So how is it possible, some of our readers have asked us over the years, for an inferior planet (like Venus) and an superior planet (like Mars) to appear in the same part of the sky?
The chart below of the inner solar system (Mercury, Venus, Earth and Mars) for January 31, 2017 helps to explain. You can see that Earth, Venus and Mars almost make a straight line in space on this date.
We are looking down upon the ecliptic (Earth’s orbital plane) from north side of the solar system, whereby all the planets orbit the sun in a counterclockwise direction. Our planet Earth rotates on its axis in a counterclockwise direction, as well, placing Venus and Mars in Earth’s evening sky.
The moon, Venus and Mars appear in nearly the same spot on the sky’s dome, but are actually nowhere close together in space. Click here to find out the present distances of Venus and Mars from Earth in astronomical units (AU).
Bottom line: As soon as darkness falls on January 31, 2017, see a beautiful trio – the moon, Venus and Mars – gracing the evening sky. Look west!
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.