Mercury and Venus Set Records

Extreme Phases of Venus and Mercury

It's a month of maxes for Mercury and Venus. As seen from the Northern Hemisphere, this month Venus reaches its highest for the Spring, its farthest north (for 5 years), and its latest setting (for 8 years). Later this month, Venus will be setting around midnight, and Mercury around 10 PM (its latest for 6 years). This will be the best sunset appearance of Mercury till 2014 (in terms of its altitude): Mercury will be 20° above the horizon — that's nearly a record. Venus's altitude of 40° is not a record, but Venus will be bright enough to make a shadow every night.

Map:

Looking west at sunset. Zenith is up. Computed for observer at latitude 35°N.

Visibility:

• Naked eye.

Details:

For a full list of Mercury and Venus events, see the calendar for May 2007.

Venus Visible at Midnight

Venus is staying up late at night these days. A comparison (see Table 1) shows that Venus sets later in 2007 than in any other recent year. But note that this is not an all-time record: These things tend to run in cycles, and rough calculations show that Venus will set one minute later every eight years for the next century or so.

Planetary Resonance

The phases of Venus repeat like clockwork every 8 years. Briefly, this happens because Venus's synodic period (the time between close approaches of Venus and Earth) is almost exactly 1.6 Earth years. And because 1.6 divides exactly into a whole number (8), it's possible to see "reruns of Venus" every 8 years, with Venus moving through the same constellations and tracing out the same paths (almost exactly) in the morning and evening sky. Compare for example these two charts for 1999 and 2007:

Planets After Dark

Northern Hemisphere observers get a rare treat this month: Like Venus, Mercury will appear at the same predictable azimuth for 40 days. Simply look 20° North of West, every night at sunset from May 10 to June 20.
Like a slow skyrocket, the planet Mercury shoots upward.
The Moon makes Mercury easy to spot on May 17.
Venus is nearly stationary this month.

Visibility:

• Sunset and evening
• Binoculars helpful