The Big Three
The top three sights for this month.
The Moon presents a disc with an apparent diameter of half a degree. Despite how large it looks in your mind’s eye, this disc is actually quite small. As an example, look to the west after the sky darkens, where you’ll find the Pleiades open cluster. If you’re not sure how to identify this, extend the line of Orion’s Belt to the right. Keep going past the bright orange star Aldebaran and eventually the line brings you to the Pleiades. Two full Moons would fit side-by-side across the longest dimension of this cluster.
The Moon occults two bright stars this month. The first occurs on the morning of 1 March when the virtually full Moon closes in on mag. +1.3 Regulus (Alpha (_) Leonis). It reaches the star with the dawn twilight well under way and despite the brightening sky, the disappearance at
06:00 UT should be fairly easy to observe. The reappearance at 06:51 UT is another matter altogether. Apart from the fact that both the Moon and Regulus will be approaching the west-northwest horizon at this time, the Sun will also be about to rise. Regulus can be seen in daylight but being low down in the sky may make spotting the reappearance challenging.
The second occurs on the night of 22 March: locate the crescent Moon in the west-southwest as darkness falls. It should be passing through the Hyades open cluster at this time. You’d think that this would result in some spectacular occultations but the Moon’s relatively small disc is able to pass surprisingly well between the brighter stars.
The first naked-eye Hyad to disappear will be mag. +4.9, 75 Tauri, which from the centre of the UK will vanish behind the Moon’s dark limb at 20:14 UT. As ever with lunar occultations, the timing will differ depending on location, so observe at least 15 minutes before the stated event time to ensure you don’t miss anything. Reappearance from the bright limb occurs almost an hour later at 21:12 UT.
The Moon manages to avoid most of the other bright stars in the southern part of the Hyades, but there are plenty of events involving the fainter members. At 23:36 UT, mag. +0.8 Aldebaran (Alpha (_) Tauri) disappears behind the Moon’s dark limb. It reappears at 00:15 UT. As with Regulus, the reappearance event occurs when the Moon and Aldebaran are close to setting, so make sure you have a good flat west-northwest horizon if you intend to observe it.
Mercury and Venus dance with one another in the evening sky this month. Things get off to an exciting start with both planets separated by less than 2° on the night of 1 March. On this date you should be able to see them 30 minutes after sunset, 5° above a flat western horizon.
Venus should be easy to spot as it’ll be really bright at magnitude –3.8, easily able to cut through the bright evening twilight. Mercury is dimmer but at mag. –1.2 it should still be easy to see as long as the atmosphere is clear low down.
The separation decreases over the next couple of evenings, being 1.4° on 2 March and 1.1° on 3 and 4 March. After that the two planets appear to separate, with Mercury appearing to move higher above Venus. This process doesn’t last, however, because Mercury’s smaller orbit caps its range and by 15 March, when it reaches its greatest eastern elongation of 18.4°, its relative climb above its Solar System neighbour comes to a halt.
After 15 March, Mercury slips back toward the Sun, while Venus continues its slow crawl in the opposite direction. A second, albeit wider, close encounter occurs on 18 and 19 March. On 18 March, Venus and Mercury appear separated by 3.8° with a very thin, 1% waxing lunar crescent close by. This will appear roughly in line with the planets.
On 19 March the 5%-illuminated Moon will have moved further east, with the planets still 3.8° apart. This distance begins to grow steadily larger over the following evenings.
The brightness of Venus remains steady over this period but Mercury dims. On 18 March, Mercury shines at mag. +0.4, dimming to +0.7 by the 19th. By the end of the month, Mercury is lost from view, Venus taking up the mantle as a beacon of the evening sky.