Mars won’t have to look hard to find a dance partner for the New Year’s Eve ball. It can only be Neptune. Beautiful, unavoidable Neptune. The Red Planet sashays up to the Blue Planet on Saturday evening Dec. 31, and you can see the sparkling couple using a pair of 50mm (or larger) binoculars or a small telescope. They’ll be close. If you’re reading this from London, the two will be ⅓° apart around 6 p.m. local time. From the U.S. Midwest that shrinks to just 0.2°, and from Honolulu to 0.016° or just 1 arc minute.
The reason the two planets get closer as you travel west is that time is passing, and Mars is moving fairly quickly across the sky. It gets dark first in London, then 6 hours later in Chicago. During that time, Mars keeps chugging to the east, getting closer to Neptune with every tick of the clock. If you keep a close watch on Mars, comparing it’s position to the surrounding stars, you can actually see it move night to night this time of year with just your eyes alone.
The two planets will be closest around 12:45 a.m. Central Standard Time on Jan. 1. Unfortunately, they will have set for the continental U.S. by that hour — but not in Hawaii. So if you’ve wisely planned a trip there over New Year’s, you’ll get to see the planets exceptionally close together.
Of course, we know that Neptune and Mars will only appear to be slow dancing because we see them along the same line of sight, like lining up your thumb with a distant mountain. In reality, Mars hovers 150 million miles from Earth that night and Neptune 2.8 billion. The distance between them is a mind-numbing 2,675,000,000 miles! Truth to tell, this couple is anything but close.
The best time to catch the event is at nightfall or around 6 p.m.- 7:30 p.m. local time. First, find outrageously bright Venus in the southwestern sky and then look about one fist held at arm’s length above and to the left of that planet to spot Mars. Mars isn’t nearly as bright as Venus, but it’s the brightest “star” in the area and unmistakably red in color. Next, point your binoculars at Mars, carefully focus until it’s as tiny a point as possible and then look immediately to the upper left of the planet for a dim twinkle of light. That’s Neptune. From Hawaii, Neptune will be to Mars’ upper right and exceptionally close. Focus is key, so make sure stars look sharp before attempting to see Neptune.
It’s fun to consider how different Mars and Neptune are. One’s a small planet just twice the size of our moon with a cold, dry, desert-like environment and an atmosphere so thin that any exposed water would boil away in seconds. Its dance partner is nearly four times the size of Earth with a vast, deep atmosphere tinted blue from icy-cold methane gas. Deep beneath those aqua clouds churns a slushy, high-pressure mix of water, methane and ammonia ices.
If you’ve never seen the solar system’s most distant planet, grab the chance New Year’s Eve night before you down too much bubbly. Speaking of which, skywatchers in northern Europe, Canada and the northern U.S. should be on the watch for aurora that night. A coronal hole in the sun’s atmosphere recently sent a spray of high speed particles our way that’s expected to arrive tomorrow afternoon and possibly fire up a G1 geomagnetic storm through the early evening hours. The moon won’t be a bother, so be sure to cast a glance northward. You’ll be looking for a low, green-hued arc and possibly some faint, feathery rays.