Northnorthnorth

Venus and Mercury are at their northernmost points – and, by chance, almost simultaneously.

The western sky after sunset. Mercury should be findable, but Mars and the stars nearest to the horizon won’t be. As for what looks like a celestial comb at top right: it’s a temporary mis-product of a campaign of revising this program, and I won’t have time to solve it until tomorrow.

For Venus the instant was May 10 at 7 hours Universal Time, for Mercury it was 8 UT. Those times were in the morning (3 and 4 AM by Eastern American clocks) and the planets are in the evening sky, so we have to see them half a day after (or before) those instants; but that makes little difference to their position.

Venus is at this northern declination (26 degrees) because it is traveling over the northerly part of the ecliptic and also happens to be (May 10 3 UT) at its maximum latitude north of the ecliptic in this orbit.

Nevertheless it is not as far north as it can be: for instance in 1996, 2004, 2012, and 2020 (all on May 4 or 5, and all 8 years apart, you’ll notice) it reached declinations of over 27 degrees. (There’s a list and discussion on page 36 of Jean Meeus’s Astronomical Tables.) Those are times when the top of its arch through the Taurus-Gemini reach coincides more closely with the very northernmost point of the ecliptic. Venus isn’t yet at its highest above our sunset horizon, because it is still moving out eastward from the Sun.

As Jack Gambino has just remarked in an email to me (he was pestering me about something else, and I told him I had to get on and write something about this evening’s scene): “We ere on the north side of our planet, looking north to see Venus and Mercury. How cool is that!”