A thin crescent moon low in the west-northwest at dusk on May 5 marks the start of Ramadan, with a month-long daytime fast beginning the next day. Nearly two weeks later, a “blue moon”—the third of four full moons within the season—is visible through all nighttime hours of May 18. Late in the month, bright Jupiter begins rising in southeast during early evening hours.
The May evening twilight chart shows that Rigel, Aldebaran, Sirius and Betelgeuse disappear this month, leaving four winter stars—Procyon, Pollux, Castor and Capella—forming an arch in the western sky through month’s end, when Mercury is just starting an evening appearance very low in the west-northwest.
Regulus in Leo crosses high in the south into the west-southwest. Golden zero-magnitude Arcturus rises high in the eastern sky, with blue-white first-magnitude Spica in Virgo to its lower right. Zero-magnitude Vega, the brightest member of the Summer Triangle and first to appear, rises into view in the northeast, with Deneb eventually trailing to its lower left. Red Antares, heart of Scorpius, rises in the southeast late in May. Bright Jupiter follows 12 degrees to Antares’ lower left, just in time for the end of May.
Nearly all the events described here are illustrated on the Abrams Planetarium Sky Calendar. Subscriptions are $12 per year at www.abramsplanetarium.org/skycalendar for three printed issues, mailed quarterly. A free, printable copy of the May 2019 issue is available at the site.
May 2 at dawn: The old moon is very low in the east, 4 degrees to the lower right of Venus.
Sunday, May 5, at dusk: The sighting of the young crescent moon low in the west-northwest, perhaps by half an hour after sunset, marks the start of Ramadan.
On May 6 at dusk: Look for the crescent moon with earthshine 3 degrees to the upper right of Aldebaran. Follow the moon nightly at dusk through May 18, watching it pass Mars on May 7, Pollux on May 9, the Beehive on May 10 (use binoculars), Regulus on May 11 and 12, and Spica on May 15.
On May 18 at dawn: The moon, some 8-9 hours before full, is low in the west-southwest. Today’s full moon is the third of four within the same season, spring 2019, so by one definition (Maine Farmers’ Almanac, 1937), it is called a “blue moon.” This definition predated the now widespread use of the term “blue moon” to refer to the second full moon within a single calendar month.
At dusk on May 18: Some 5-6 hours after full, the moon is very low in the east-southeast. From the Coachella Valley on May 18, the moon sets in the west-southwest about 5 minutes after sunrise, and rises in the east-southeast about a minute after sunset, but unless you’re at a site higher than your surroundings, it will not be possible to view the sun and moon simultaneously.
Two hours after sunset on May 18: Find Antares 11 degrees below the full moon; on May 19, find Jupiter 7 degrees to the moon’s lower left; and on May 20, see the moon rising 6 degrees to the lower left of Jupiter. Rather than stay up late, you can switch to mornings to catch the waning gibbous moon passing Antares, Jupiter and Saturn May 19-23. The last quarter occurs May 26. Finally, catch the last old crescent near Venus on June 1.
(Almost) opposing planets: On May 20, Jupiter rises about one hour before Mars sets. About two hours after sunset, both planets are about 5 degrees above opposite horizons. It’ll get easier to view both planets simultaneously in coming weeks, as Jupiter rises earlier.
Mars fades from magnitude +1.6 to +1.8 in the west-northwest at dusk. Watch Mars pass between Beta and Zeta Tauri, tips of Bull’s horns, on May 6. Crossing into Gemini on May 16, Mars goes 2 degrees north of Eta and Mu, third-magnitude stars 1.9 degrees apart in Castor’s foot, May 21-24. On May 31, Mars is 0.9 degrees south of third-magnitude Epsilon Gem.
Late evening until dawn: Bright Jupiter, in Ophiuchus, on May 1 rises within 15 degrees to the lower left of Antares, three hours and 10 minutes after sunset, as Mars sets. Saturn in Sagittarius rises within two hours later. Jupiter rises half an hour earlier each week, and by May 31 rises 12 degrees to the lower left of Antares 40 minutes after sunset, with Saturn still following by two hours. Jupiter (magnitude -2.5 to -2.6) and Saturn (+0.5 to +0.3) brighten slowly and stay 27-29 degrees apart, as both retrograde, by 3.0 degrees and 0.8 degrees, respectively. Jupiter passes 2.5 degrees north of 3.3-magnitude Theta Oph May 23-24.
On May 24, best in the darkness hours before dawn: Jupiter, moving retrograde, or westward against the stars, passes 2.5 degrees north of the 3.3-magnitude star Theta in Ophiuchus. Jupiter passed that star while going eastward on Feb. 27.
In the morning twilight, find bright Jupiter in the south-southwest to southwest, getting lower as the month progresses, with red Antares, heart of Scorpius, 15 to 12 degrees to its lower right; and Saturn, passing through the south during May; and Venus, very low in the east to east-northeast in brightening twilight. Binoculars may show Mercury to the lower left of Venus for the first few days. The morning twilight chart below shows all that, plus the Summer Triangle of Vega, Altair and Deneb passing overhead; golden Arcturus sinking in the west to west-northwest; and Fomalhaut, Mouth of the Southern Fish, low in the southeast.
Check the website of the Astronomical Society of the Desert at www.astrorx.org for dates and times of our evening star parties. Sawmill Trailhead, our high-altitude site (elevation 4,000 feet), will have sessions starting at dusk on Saturdays, May 4 and June 1. Our primary, more-accessible location is at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument (on Highway 74, within four miles south of Highway 111 in Palm Desert). Our final one for the season will be on Saturday, May 11, from 8 to 10 p.m.
Also, remember to check the Impromptu Star Parties link on the Astronomical Society’s webpage. I’ll be offering a Ramadan Young Moon Watch on Sunday, May 5, at a yet-to-be-selected site with a view toward the west-northwest horizon, and other sky watches in Palm Springs at the pedestrian bridge over Tahquitz Creek at North Riverside Drive and Camino Real.
Wishing you clear skies!
Robert Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing sky watching opportunities for a variety of groups in the Coachella Valley. Robert Miller 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.