Keep your fingers crossed for clear skies on the evening of Feb. 10, and mark your calendars to remind yourself to spend the hour after sunset gazing at the western sky. Sunset is about 6 p.m. that night. You’ll probably be able to spot Venus, high in the western sky even before the sun drops below the horizon. As evening twilight deepens, Venus will intensify to its full magnificence at a magnitude of negative 4 and be joined by Mercury which will be at its greatest elongation (widest separation from the sun).
Look carefully at the darkening sky surrounding Venus to detect the zodiacal light. The geometry will be perfect that night (and for the first couple of weeks in February) to illuminate the cloud of comet dust that perpetually orbits the sun. It will appear as a triangular glow that reaches high into the western sky and perhaps as bright as the Milky Way for the first few minutes after twilight ends at 7:25 p.m.
Point a telescope at Mercury and you will see that it displays a half disk like a quarter moon. If you’ve been watching Mercury since the first of the month, you will have followed its changing shape night after night from a 6 arc-second disk on the 1st to a 7 arc-second quarter shape on the 10th.
This same night is an excellent opportunity to detect the faint blue disk of the planet Neptune when it passes very close to a 4th magnitude star (Phi Aquarii). The pair will lie on the imaginary line connecting Mercury and Venus about 1/3 of the way from Mercury and will make an easy target for binoculars. The star is a red giant that will appear a warm reddish-yellow in stark contrast to the blue disk of the planet. They will be very uneven in brightness with the star appearing about 30 times brighter even though it is some 6,000 times more distant!
An extra treat will be provided by the International Space Station which will enter the scene at about 7:15 and take a couple of minutes to arc across the western sky looking very much like a quickly moving bright star.
The eastern sky in the pre-dawn hours of the 18th is the stage for an occultation of Mars. A 24-day old crescent moon (26% illuminated) will cover the tiny disk of the planet at about 4:38 in the morning. The disappearance of Mars will take place just about 10 degrees above the southeastern horizon which may make it rather difficult to observe. The bright limb of the moon will most likely overwhelm the much dimmer planet. You have a better chance of witnessing Mars’ reappearance at 5:39 when the moon is almost 20 degrees up. Mars will pop out from behind the dark limb of the moon just at the start of morning twilight. Jupiter and Saturn will be following the pair into the daytime sky and both should be visible before sunrise at 7 a.m.
Earlier in the month on the 13th, the moon will occult the main belt asteroid Juno at about 2:37 a.m. The 10th magnitude asteroid will be hard to pick out as the bright moon (almost -12 magnitude) approaches, but Juno will be detectable in a telescope during the preceding hour and you might find that you can keep it in view almost until the moon’s limb covers it. It will be a glancing blow, and the tiny rock will emerge an hour later at 3:29.