Moon sweeps past Mars January 11 to 13
On January 11, 12 and 13, 2019, use the waxing crescent moon to find the red planet Mars. You’ll find both Mars and the moon in the evening sky, with the moon in a waxing crescent phase and Mars much fainter than it was six months ago, when it outshone all the stars, brighter than since 2003. Now, Mars is still shining as brightly as a 1st-magnitude star. It’ll be that bright “star” close to the moon on these evenings.
Of course, when we say the moon and Mars are close together, we mean they are close together on our sky’s dome. These two worlds are not particularly close together in space. When you see them, know that our moon lies about a quarter million miles (400,000 km) away, whereas Mars – a neighboring planet – lodges way beyond the moon, at some 467 times the moon’s distance.
The moon appears large in Earth’s sky because it’s close to us, relative to Mars. Meanwhile, Mars’ diameter is roughly twice that of the moon, yet Mars’ surface area exceeds that of the moon by about 4 times. Still, to the eye, Mars appears starlike in our sky – like a point, not a disk – because it’s so much farther away than the moon.
Even when Mars made its closest pass to Earth since Stone Age times on August 27, 2003, the red planet’s angular diameter was only 1/74th the moon’s angular diameter. In other words – contrary to a persistent internet hoax that has circulated each year since 2003 – Mars never comes anywhere close to appearing as large as the moon in Earth’s sky.
In many respects, Mars is the most earthlike planet. The tilt of Mars’ spin axis is almost the same as Earth’s (25.19 degrees versus 23.26 degrees), and day length on Mars and Earth almost match (24.6 hours versus 24 hours). The mean temperate of Earth most resembles that of Mars, though Mars is quite a bit colder: -85 degrees F (-65 degrees C) versus 59 degrees F (15 degrees C). And, quite by coincidence, Mars’ surface area pretty much equals Earth’s land area.
Want to know more? Check out this planetary fact sheet.
Bottom line: These next several evenings – January 11 to 13, 2019 – use the waxing crescent moon to locate Mars, the fourth planet outward from the sun, and the next planet outward from Earth.
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.
Published on EarthSky.org