Venus, the brilliant planet in the west at dusk, ascends to its highest position in the evening sky this month— while the stars temporarily surrounding it steadily drop away.
Use monthly evening twilight sky chart to track Venus, Mars and bright stars. During May, watch Rigel, the Pleiades, Aldebaran, Sirius and Betelgeuse, in order, exit the western sky, leaving the “Spring Arch” of Procyon, Pollux, Castor and Capella to remain at month’s end.
The May 2023 Sky Calendar, illustrating many of the events described in this column, together with a constellation map for the month’s evening sky, are available for free here.
Venus,at magnitude -4.1 to -4.4, rules the evening sky! Throughout May, Venus remains above the unobstructed horizon for more than three hours after sunset. If observed at sunset or in twilight in early May, Venus attains its greatest altitude for this entire evening apparition: In May’s second week, Venus is nearly 41° up at sunset and 32° up at mid-twilight (when the sun is 9° below the horizon). Even at nightfall, when twilight ends with the sun 18° down, Venus is still 22° up on May 1, and 18° up on May 31. This month, Venus can be spotted in daylight, 43° to 45° to the upper left of the setting sun. Near the time of sunset or not long after is best for using a telescope to follow Venus’ changing appearance. In May, the disk grows from 17 to 23 arcseconds across, while its phase decreases from about two-thirds to just over half illuminated (66% to 52%). In June, the crescent Venus will become large enough to be resolved even through binoculars!
Evening events: As the sky darkens on May 1, Venus appears between Beta and Zeta Tauri, tips of the Bull’s horns. Find faint Mars, of magnitude +1.4, nearly 26° to Venus’ upper left, in Gemini, 6° below Pollux. As Venus shifts 1.1° to 1°, and Mars shifts nearly 0.6° daily against stars this month, watch for these events: On May 8, Mars is 5° south of Pollux. On May 10-12, Venus passes 3.6° north of third-magnitude stars Eta and Mu in the foot of Castor in Gemini. On May 16, Mars-Pollux-Castor are in a straight line, and Venus is 0.7° north of third-magnitude Epsilon Gem.
On May 20, the young moon, a 2% crescent, appears very low in the west-northwest at dusk, 28° to the lower right of Venus. On May 21, the 7% crescent moon is 16° to the lower right of Venus. The brilliant planet forms an isosceles triangle with Pollux and Castor, within 9° of each.From May 22-24, watch the moon pass Venus, Pollux, Castor and Mars. On May 22, the 12% moon appears 5° to the lower right of Venus. By May 23, the moon has leapt to nearly 7° to Venus’ upper left while waxing to 19%. Pollux appears an exceptionally close 2° to the moon’s upper right, while Mars appears within 9° to the moon’s upper left. On May 24, the 27% moon is nearly 5° above Mars.
On May 26, the 46% moon, almost at first quarter (half full) phase, is within 4° to the upper right of Regulus, heart of Leo. On May 28 and 29, Venus passes 4° south of Pollux. On May 30, the moon (now gibbous, at 82%) appears 5° to the upper right of Spica, while Mars passes aphelion, the point in its orbit most distant from sun. On May 31, the Venus-Mars gap has closed to 11°, while Mars has faded to magnitude +1.6. On June 1, Venus-Pollux-Castor are arranged in a straight line; Mars appears in the Beehive Cluster that night and next. Use binoculars or a telescope after nightfall to see the cluster’s brightest stars, of sixth and seventh magnitudes.
Morning events: Saturn, in Aquarius, glows at magnitude +0.9 in the east-southeast to southeast as dawn brightens. A telescope shows the rings tipped only 8.0° to 7.4° from edgewise.
On May 7, the red star Antares, heart of the Scorpion, appears just 1.5° east (to the left) of the 96% moon. Earlier that morning, the moon will occult Sigma in Scorpius, the third-magnitude star just west-northwest (to the right) of Antares, and one of the “outworks of the heart.”
Seen from Reno, the star’s disappearance behind the moon’s leading sunlit edge occurs at 2:48 a.m., with the reappearance at the moon’s trailing dark edge at 3:44 a.m. A telescope will be required to observe disappearance and reappearance.
In the brightening dawns in May, the Summer Triangle of Vega, Altair and Deneb passes overhead; Arcturus sinks low in the west to west-northwest; and Antares sinks low in the southwest. Fomalhaut, mouth of the Southern Fish, appears far to the lower right of Saturn. Jupiter rises into prominence in the eastern sky later in the month. See our morning twilight chart with the online version of this article.
On May 13, a fat 41 percent crescent moon appears near Saturn. On May 16, locate recently emerged Jupiter (magnitude -2.1) very low, north of east, 14°-15° to the lower left of the 12 percent waning crescent moon. On May 17, a 6 percent moon occults Jupiter. From most of California and Western Nevada, Jupiter is already hidden at moonrise. From Reno, Jupiter reappears at the moon’s upper dark edge between 5:19 and 5:20 a.m. Since the event occurs in bright twilight shortly before sunrise, the use of a telescope is recommended.
Mercury, to the lower left of Jupiter, brightens from a too-faint magnitude +1.6, when 6° from Jupiter (hidden by the moon) on May 17, to +1.0 when 7° from Jupiter on May 22; and to magnitude +0.4 when 12° from Jupiter on May 31. On May 28, Saturn appears at quadrature, 90° west of the sun. Spaceship Earth is then heading directly toward Saturn. Use a telescope so see Saturn’s shadow cast upon the rings, at the west-northwest limb of the planet.
Visible all night: On May 31, Antares, red supergiant heart of the Scorpion, appears at opposition to the sun. Look for it low in the southeast at dusk, highest in the south in middle of night, and low in the southwest at dawn. Its positions at dusk and dawn are shown on our two twilight charts.
Graphs plotting the evening planets’ setting times in relation to sunset, and morning planets’ rising times in relation to sunrise, make it easy to know when to look for the planets the rest of this year. For example, Venus will disappear from the western evening sky in July, and quickly reappear in the eastern morning sky in late August.
The Astronomical Society of the Desert will host a star party on Saturday, May 13, at the Santa Rosa and San Jacinto Mountains National Monument Visitor Center; and on Saturday, May 20, at Sawmill Trailhead, a site in the Santa Rosa Mountains at elevation 4,000 feet. For dates and times of these and other star parties in 2023, and maps and directions to the two sites, visit astrorx.org.
Robert C. Victor originated the Abrams Planetarium monthly Sky Calendar in October 1968 and still produces issues occasionally, including May 2023. He enjoys being outdoors sharing the beauty of the night sky and other wonders of nature. Robert Miller, who provided the evening and morning twilight charts, did graduate work in planetarium science and later astronomy and computer science at Michigan State University, and remains active in research and public outreach in astronomy.
