Mercury enters the May 2020 evening sky as Venus exits.
by Jeffrey L. Hunt
Venus passes between our planet and the sun (inferior conjunction) early next month to emerge into the morning sky. As this occurs, Mercury enters the sky for its short evening appearance. The moon joins the pair on a few nights.
Venus is the brilliant “star” in the west-northwest after sunset. As Mercury enters the sky, it is a bright star, much dimmer than Venus, but visible without optical help. As it rises higher in the sky, a binocular is needed to see it as it dims. Over several evenings, it appears to move from the lower right of Venus to its upper left, while the star Elnath is nearby.
The planets are reasonably low in the sky. Find a clear horizon toward the west-northwest.
YouTube video about Venus and Mercury, May 2020
In the notes that follow, the “m” numbers are measures of the planets’ brightness. The lower the number, the brighter the celestial object. The sun has the lowest value (−26.5) on this scale. Afterall it is so bright it creates daytime on our planet and shines on the moon and other planets in its system. Notice how Mercury’s number increases during the days described. It starts out bright and then dims. At the end of the sequence it is reasonably bright, but it is further dimmed by the brightness of twilight. Use a binocular each evening to first locate the speedy planet and then attempt to locate it without the binocular’s assistance. Mercury is almost always seen during morning twilight or evening twilight.
We measure sizes and separations in the sky with angles, using degrees as we do with a protractor. When we observe the sky, the objects seem to be different sizes because of their actual sizes and their distances. The moon’s apparent size seems large, about 0.5° as measured in angular units. The sun is farther away than the moon, but it appears the same size. Because they appear to be the same size, the moon can cover the sun to create a solar eclipse. The tip of your pinky finger on your outstretched arm easily covers a full moon. Try it the next time you see a brilliant full phase.
The space that your outstretched fist covers is about 10°. On the first date in the description below, Mercury is nearly 5° to the lower right of Venus. That’s about half a fist. On the second day, Venus is about two outstretched finger tips from Venus.
If you have a small telescope, look at Venus. It’ll show a thin crescent! Here’s what to look for:
May 19: Forty-five minutes after sunset, Venus (m = −4.4), over 11° up in the west northwest, is 2.7° below Elnath and 4.9° to the upper left of Mercury (m = −0.8). Betelgeuse is less than 5° up in the west. What is the last date that you see it before it disappears into the sun’s glare? Venus sets at the end of evening twilight, nearly 2 hours after sunset.
May 20: Forty-five minutes after sunset, Venus is over 10° up in the west-northwest. The Venus – Elnath gap is 3.0°, and Mercury (m = −0.7) is 2.8° to the lower right of brilliant Venus. Through a telescope, the Venus is 53” across and 6% illuminated, a magnificent evening crescent!
May 21: Forty-minutes after sunset, Venus (m = −4.3) – over 9° up in the west-northwest – is 1.1° to the upper right of Mercury (m = −0.6), a conjunction. The Venus – Elnath gap is 3.4°.
May 22: In the early evening sky, Venus, Mercury (m = −0.5), and Elnath make a compact triangle. Venus is 1.6° to the lower right of Mercury; Venus is 3.8° below Elnath; and the Mercury – Elnath gap is 3.4°. Tomorrow evening the moon enters the scene. Jupiter is now rising before midnight CDT.
May 23: At 45 minutes after sunset, find a clear horizon to view the scene in the west. Venus, 7.0° up in the west-northwest, is 4.5° to the upper right of the crescent moon (1.3 days past the New phase, 2% illuminated). The Venus – Elnath gap is 4.2°. Mercury (m = −0.4) is 3.5° to the upper left of Venus and 3.1° to the lower left of Elnath.
May 24: Forty-five minutes after sunset, Venus is about 6° up in the west-northwest. Find a clear horizon to see it. The planets and the star make a triangle. Mercury is 5.5° to the upper left of Venus, nearly midway from Venus to the moon that is nearly 12° to the upper left of Venus, although Mercury is above a line that connects Venus and the moon. Elnath is 4.6° above Venus and 3.5° to the upper right of Mercury. Venus’ elongation is 15°.
May 25: Forty-five minutes after sunset, Venus (m = −4.1) is about 4° up in the west-northwest. The planet continues to make a triangle with Mercury (m = −0.2) and Elnath. Venus is 5.1° to the lower right of the star, while Mercury is 4.5° to the upper left of Elnath. Venus is 7.5° to the lower right of Mercury. Venus sets at Nautical Twilight – the time when the natural horizon is barely distinguishable – over an hour after sunset. The observing window is rapidly closing to see Venus during this apparition. The gaps of the two planets and star continue to grow as Venus disappears into brighter twilight. Through a telescope, the brilliant planet is 56” across and 3% illuminated. As the sky darkens to show more stars, the moon (3.4d, 11%) is in central Gemini, over 11° to the lower right of Pollux (β Gem, m = 1.2), and over 17° to the upper left of Mercury.
May 26: Forty-five minutes after sunset, Venus – about 3° up in the west-northwest – is 5.7° below Elnath and 9.5° to the lower right of Mercury (m = −0.2). Mercury is 5.7° to the upper left of the star. As the sky darkens further the moon (4.4d, 19%) is 5.9° to the left of Pollux.
Before the days described in this article, Venus passed close to Elnath in a quasi-conjunction.
Read more about that here.
For a semitechnical description of the month’s planet activities, click here.
For more about Venus as an Evening Star, read this article.