Western Slope Skies - Mercury In the Evening

Mar 24, 2017

Mercury, the innermost and speediest planet, can be hard to see, because it never appears very far from the brilliant Sun in our sky.

But Mercury may be visible just after sunset from March 24 to around April 12, as it moves out from behind the Sun, only to pass nearly in front of our central star on April 19. To see Mercury, you’ll need clear and transparent skies and an unobstructed western horizon. After the Sun sets at about 7:25 p.m. on March 24, look to the west at about 7:52. You may see Mercury about 10 degrees above the horizon – that’s the width of about 2 fists held at arm’s length. If Mercury is not obvious to your unaided eyes – try using binoculars to spot it. But, be sure that the Sun has set before pointing your binoculars west – looking at the Sun without proper filters can result in blindness.

On March 28, at 7:53 p.m. a thin crescent Moon lies below and slightly to the left of Mercury. By the next evening, March 29, at 7:53, a slightly fatter crescent Moon has moved above and left of Mercury. On April 1, Mercury’s offset from the Sun appears greatest. But Mercury has faded a bit since March 24, as the percentage of its Sun-illuminated disk visible from Earth in telescopes has decreased from 70% to 50%.  After April 1, Mercury appears to move rapidly toward the Sun, and it continues to fade, as its Sun-illuminated disk dwindles from 50% to a slender crescent, only 7% illuminated on April 12. Because of its close-in obit, speedy Mercury revolves around the sun in only 88 days. After April 12, Mercury will re-appear in the evening sky during July.

Western Slope Skies is produced by members of the Black Canyon Astronomical Society. This episode was written and recorded by Art Trevena.