May 2021 Celestial Calendar

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Dave Mitsky
Post subject: May 2021 Celestial Calendar
Posted: Mon May 31, 2021 8:51 pm
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May Celestial Calendar by Dave Mitsky

All times, unless otherwise noted, are UT (subtract four hours and, when appropriate, one calendar day for EDT)

5/3 Saturn is at western quadrature (90 degrees from the Sun) at 10:00; the Moon is 4.0 degrees south of Saturn at 17:00; Last Quarter Moon occurs at 19:50; Mercury is 2.0 degrees south of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 22:00
5/5 Today is Beltane, a cross-quarter day; the Moon is 4.4 degrees southeast of Jupiter at 1:00; the Curtiss Cross, an X-shaped clair-obscur illumination effect located between the craters Parry and Gambart, is predicted to be visible at 13:04
5/6 The peak of the Eta Aquarid meteor shower (a zenithal hourly rate of 20 per hour for northern hemisphere observers) occurs at 2:00; the Moon is 4.0 degrees southeast of Neptune at 22:00
5/7 Mercury is at its northernmost latitude from the ecliptic plane (7.0 degrees) at 6:00
5/8 Mars and Saturn are at heliocentric opposition (longitudes 127.5 degrees and 307.5 degrees) at 7:00
5/9 Venus is 4.1 degrees southeast of M45 at 11:00; Venus is at the ascending node through the ecliptic plane at 15:00
5/10 Mercury is 7.9 degrees north of the first-magnitude star Aldebaran (Alpha Tauri) at 4:00
5/11 The Moon is 2.2 degrees southeast of Uranus at 0:00; New Moon (lunation 1217) occurs at 19:00; the Moon is at apogee, subtending 29' 24'' from a distance of 406,512 kilometers (252,595 miles), at 21:53
5/12 The Moon is 5.0 degrees southeast of M45 at 15:00; the Moon is 0.7 degrees south of Venus, with an occultation occurring at Easter Island, eastern Polynesia, and most of New Zealand, at 22:00
5/13 The Moon is 5.4 degrees north-northwest of Aldebaran at 9:00; the Moon is at ascending node (longitude 70.7 degrees) at 11:00; the Moon is 2.0 degrees south of Mercury at 18:00; the equation of time, the difference between mean solar time (as indicated by clocks) and apparent solar time (as indicated by sundials), is at a maximum of 3.65 minutes at 20:00
5/14 The Sun enters Taurus (longitude 53.5 degrees on the ecliptic) at 2:00
5/15 The Moon is 1.1 degrees north of the bright open cluster M35 in Gemini at 7:00
5/16 The Moon is 1.5 degrees north-northeast of Mars at 6:00; the Moon is 6.7 degrees south of the first-magnitude star Castor (Alpha Geminorum) at 20:00
5/17 The Moon is 3.1 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 1:00; Venus is 5.8 degrees north of Aldebaran at 4:00; Mercury is at greatest eastern elongation (22.0 degrees) at 6:00; Mercury is at its northernmost declination (25.2 degrees) at 20:00
5/18 The Moon is 3.1 degrees north-northeast of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 4:00; the Lunar X (the Purbach or Werner Cross), an X-shaped clair-obscur illumination effect involving various rims and ridges between the craters La Caille, Blanchinus, and Purbach, is predicted to be visible at 23:41
5/19 First Quarter Moon occurs at 19:12; the Moon is 4.7 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 22:00
5/20 The Sun's longitude is 60 degrees at 20:00
5/21 Jupiter is at western quadrature (90 degrees from the Sun) at 15:00
5/23 A double Galilean shadow transit (Calisto's shadow follows Io's) begins at 15:15; the Moon is 5.9 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 19:00; Saturn is stationary, with retrograde (western) motion to begin, at 20:00
5/26 The Moon is at perigee, subtending 33' 26'' from a distance of 357,312 kilometers (222,023 miles), at 1:50; Full Moon, known as the Milk or Planting Moon and the largest Full Moon of the year, occurs at 11:14; a total lunar eclipse begins at 8:47 and ends at 13:49; the Moon is 4.6 degrees north-northeast of Antares at 20:00; the Moon is at the descending node (longitude 250.7 degrees) at 20:00
5/27 Mars is 8.7 degrees south of the first-magnitude star Castor (Alpha Geminorum) at 2:00
5/28 A double Galilean shadow transit (Io's shadow follows Ganymede's) begins at 21:28
5/29 Mercury is 0.4 degrees south of Venus at 6:00; Mercury is 7.6 degrees west of M35 at 16:00
5/30 Mercury is stationary, with retrograde (western) motion to begin, at 2:00; Mercury is at the descending node through the ecliptic plane at 16:00
5/31 The Moon is 4.1 degrees southeast of Saturn at 4:00

Nicolas Lacaille (1713-1762), Otto Wilhelm Struve (1819-1905), Joseph Lockyer (1836-1920), Williamina Fleming (1857-1911), and Frank Drake (1930) were born this month.

The first recorded perihelion passage of Comet Halley (1P/Halley) occurred on May 25, 240 BC. Thales of Miletus accurately predicted a solar eclipse on May 28, 585 BC. The German astronomers Gottfried and Maria Magarethe Kirch discovered the bright globular cluster M5 on May 5, 1702. On May 1, 1759, the English amateur astronomers John Bevis and Nicholas Munckley observed Comet Halley on its first predicted return. The French astronomer Charles Messier discovered the globular cluster M3 on May 3, 1764 and the globular cluster M10 on May 29, 1764. The Italian astronomer Annibale de Gasparis discovered asteroid 11 Parthenope on May 11, 1850. Asteroid 14 Irene was discovered on May 19, 1851 by the English astronomer John Russell Hind. The German astronomer Robert Luther discovered asteroid 26 Proserpina on May 6, 1853. The Australian astronomer John Tebbutt discovered the Great Comet of 1861 on May 13. The English astronomer Norman Pogson discovered asteroid 80 Sappho on May 2, 1864. Norman Pogson discovered asteroid 87 Sylvia on May 16, 1866. The 40-inch Clark refractor at the Yerkes Observatory saw first light on May 21, 1897. The Griffith Observatory opened to the public on May 14, 1935. Nereid, Neptune’s third-largest satellite, was discovered on May 1, 1949 by the Dutch-American astronomer Gerard Kuiper.

The broad peak of the Eta Aquarid meteor shower is unaffected by a waning crescent Moon this year. Eta Aquarid meteors are debris from the famous periodic comet 1P/Halley. The radiant is located close to the Water Jug asterism in Aquarius. Southern hemisphere observers are favored. See ... +Aquariids and page 50 of the May 2021 issue of Sky & Telescope for additional information on the Eta Aquarids.

Information on passes of the ISS, the USAF’s X-37B, the HST, Starlink, and other satellites can be found at

The Moon is 18.9 days old, is illuminated 79.5%, subtends 32.6 arc minutes, and is located in Sagittarius on May 1st at 0:00 UT. The Moon is at its greatest northern declination on May 16th (+25.6 degrees). The Moon is at its greatest its greatest southern declination on May 1st (-25.5 degrees) and on May 29th (-25.6 degrees). Longitudinal libration is at maximum (+7.2 degrees) on May 4th and at minimum (-7.8 degrees) on May 20th. Latitudinal libration is at maximum (+6.8 degrees) on May 6th and at minimum (-6.8 degrees) on May 21st. Favorable librations occur for the following craters: Phocylides (May 25th), Short (May 26th), and Mare Undarum (May 27th). The Curtiss Cross is visible on May 5th and the Lunar X on May 18th. The Moon is at apogee (distance 63.73 Earth-radii) on May 11th and at perigee (distance 56.02 Earth-radii) on May 26th. New Moon occurs on May 11th. Large tides will occur after the Full Moon on May 26th. A total lunar eclipse that's visible throughout the Pacific Ocean and parts of eastern Asia, Japan, Australia, western South America, and western North America takes place on May 26th. Greatest eclipse occurs at 11:18:43 UT1 (11:19:53 TD). For more on the eclipse, the 55th of Saros 121, see ... prime.html and the article on pages 48 and 49 of the May 2021 issue of Sky & Telescope. The Moon occults Venus on May 12th from certain parts of the world. Browse for additional information on this and other lunar occultation events. Visit ... the-stars/ for tips on spotting extreme crescent Moons and for Full Moon and other lunar data. Browse ... oonMap.pdf and for simple lunar maps. Visit to download the free Virtual Moon Atlas. Consult for current information on the Moon. See for a lunar phase and libration calculator and ... AXwF1SizSg for the Lunar Reconnaissance Orbiter Camera (LROC) Quickmap. Click on for a lunar phase calendar for this month. Times and dates for the lunar crater light rays predicted to occur this month are available at

The Sun is located in Aries on May 1st. It enters Taurus on May 14th.

Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on May 1st: Mercury (magnitude -1.1, 5.7", 83% illuminated, 1.19 a.u., Aries), Venus (magnitude -3.9, 9.8", 99% illuminated, 1.70 a.u., Aries, Mars (magnitude +1.6, 4.6", 93% illuminated, 2.02 a.u., Gemini), Jupiter (magnitude -2.2, 37.4", 99% illuminated, 5.27 a.u., Aquarius), Saturn (magnitude +0.7, 16.7", 100% illuminated, 9.96 a.u., Capricornus), Uranus on May 16th (magnitude +5.9, 3.4", 100% illuminated, 20.74 a.u., Aries), Neptune on May 16th (magnitude +7.9, 2.2", 100% illuminated, 30.38 a.u., Aquarius), and Pluto on May 16th (magnitude +14.3, 0.1", 100% illuminated, 33.78 a.u., Sagittarius).

In the evening, Mercury, Venus, and Mars are in the west. Jupiter and Saturn can be found in the southeast and Uranus and Neptune in the east at dawn.

Mercury undergoes its best apparition of the year for northern hemisphere observers this month. It's in superior conjunction on May 1st. Mercury is two degrees south of M45 on May 3rd. The Moon passes 2.1 degrees southeast of Mercury on May 13th. Mercury is at greatest eastern elongation on May 17th. Mercury is only 0.4 degrees southeast of Venus on May 29th. The speediest planet is 7.6 degrees west of M35 on the same date. Mercury is stationary and is at the descending node through the ecliptic plane on May 30th. An article on observing Mercury during May appears on pages 49 and 50 of the May 2021 issue of Sky & Telescope.

Venus shines at magnitude -3.9 for most of May. Over the course of the month, its apparent diameter increases by only 0.5 arc seconds. Venus increases in elongation from the Sun from 9 to 17 degrees this month. The most brilliant planet is at the ascending node on May 9th. A young crescent Moon passes less than one degree south of Venus on May 12th. Mercury and Venus remain in close proximity throughout the month and are in conjunction on May 29th.

Mars remains a poor target for observation with an angular diameter of only four arc seconds. Mars begins the month 2.3 degrees due north of the third-magnitude star Tejat (Mu Geminorum), spends May 8th to May 10th within one degree of the third-magnitude star Mebsuta (Epsilon Geminorum), and ends the month five degrees south of first-magnitude star Pollux (Beta Geminorum). The Red Planet shines at magnitude +1.7 as it forms a triangle with Castor and Pollux late in the month. Mars and Saturn are at heliocentric opposition on May 8th. The waxing crescent Moon passes 1.5 degrees north-northeast of Mars on May 16th.

During May, Jupiter grows in apparent diameter from 37.4 to 41.1 arc seconds and brightens to magnitude -2.4. It rises around 2:00 a.m. local DST by mid-month. The waning crescent Moon passes five degrees to the south of Jupiter on May 5th. Browse ... ing-tools/ or in order to determine transit times of Jupiter’s central meridian by the GRS. GRS transit information also appears on pages 50 and 51 of the May 2021 issue of Sky & Telescope. A list of selected Galilean satellite mutual events taking place this month can be found on page 50 of May 2021 issue of Sky & Telescope. Double Galilean shadow transits take place on May 23rd and May 28th. Data on other Galilean satellite events is available on page 51 of the May 2021 issue of Sky & Telescope and online at ... ing-tools/

Saturn shines at magnitude +0.6 as the month progresses and has an apparent equatorial diameter of over 17 arc seconds. Its rings subtend about 40 arc seconds. Saturn is at western quadrature on May 3rd. Saturn reaches its first stationary point on May 23rd and then begins to retrograde. Saturn has conjunctions with the Last Quarter Moon on May 3rd and the waning gibbous Moon on the night of May 30th-May 31st, with the Moon passing about four degrees south of the planet on both occasions. Titan, which is Saturn’s brightest satellite at magnitude +8.4, is located 2.8 arc seconds east of the planet on May 3rd. It lies south of Saturn on 7th and May 23rd and north of it on May 15th and May 31st. Saturn’s peculiar satellite Iapetus fades to 12th magnitude as it heads toward greatest eastern elongation on May 25th. For further information on Saturn’s satellites, browse ... ing-tools/

Uranus can be seen once again low on the eastern horizon at dawn during the latter part of the month. It lies about eleven degrees below Hamal (Alpha Arietis).

Neptune is low in the east at dawn.

The dwarf planet Pluto is fairly low in the south as morning twilight begins.

During May, Comet C/2020 R4 (ATLAS) glides southwestward through Coma Berenices coming close to a number of galaxies. The comet lies about five degrees north of the sixth-magnitude globular cluster M3 on May 1st and passes less than three degrees south of the ninth-magnitude spiral galaxy NGC 4631 (the Whale Galaxy) and even closer to the tenth-magnitude spiral galaxy NGC 4656 (the Hockey Stick Galaxy) on May 5th. Comet ATLAS is located just north of the tenth-magnitude elliptical galaxy NGC 4278 on May 8th. Visit and and for additional information on this and other comets visible this month.

Asteroid 4 Vesta shines at seventh magnitude as it heads southeastward through eastern Leo this month. Far fainter at eleventh magnitude, asteroid 29 Amphitrite also travels southeastward through Leo, passing very close to Regulus on May 13th. Asteroid 230 Athamantis (magnitude +10.3) is at opposition in Scorpius on May 21st. Information on asteroid occultations taking place this month is available at

For more on the planets and how to locate them, browse

A wealth of current information on solar system celestial bodies is posted at and

Information on the celestial events transpiring each week can be found at and and ... -a-glance/

Free star maps for June can be downloaded at and ... Star-Chart and
Data on current supernovae can be found at

Finder charts for the Messier objects and other deep-sky objects are posted at and and ... l-june.htm

Telrad finder charts for the Messier Catalog and the SAC’s 110 Best of the
NGC are posted at ... s/map1.pdf and ... estNGC.pdf respectively.

Information pertaining to observing some of the more prominent Messier galaxies can be found at ... tronomers/

Stellarium and Cartes du Ciel are two excellent freeware planetarium programs that are available at and

Deep-sky object list generators can be found at and and

Freeware sky atlases can be downloaded at ... s-full.pdf and ... arts-r1021 and

Eighty binary and multiple stars for May: 1 Bootis, Struve 1782, Tau Bootis, Struve 1785, Struve 1812 (Bootes); 2 Canum Venaticorum, Struve 1624, Struve 1632, Struve 1642, Struve 1645, 7 Canum Venaticorum, Alpha Canum Venaticorum (Cor Caroli), h2639, Struve 1723, 17 Canum Venaticorum, Otto Struve 261, Struve 1730, Struve 1555, h1234, 25 Canum Venaticorum, Struve 1769, Struve 1783, h1244 (Canes Venatici); 2 Comae Berenices, Struve 1615, Otto Struve 245, Struve 1633, 12 Comae Berenices, Struve 1639, 24 Comae Berenices, Otto Struve 253, Struve 1678, 30 Comae Berenices, Struve 1684, Struve 1685, 35 Comae Berenices, Burnham 112, h220, Struve 1722, Beta Comae Berenices, Burnham 800, Otto Struve 266, Struve 1748 (Coma Berenices); h4481, h4489, Struve 1604, Delta Corvi, Burnham 28, h1218, Struve 1669 (Corvus); H N 69, h4556 (Hydra); Otto Struve 244, Struve 1600, Struve 1695, Zeta Ursae Majoris (Mizar), Struve 1770, Struve 1795, Struve 1831 (Ursa Major); Struve 1616, Struve 1627, 17 Virginis, Struve 1648, Struve 1658, Struve 1677, Struve 1682, Struve 1689, Struve 1690, 44 Virginis, Struve 1719, Theta Virginis, 54 Virginis, Struve 1738, Struve 1740, Struve 1751, 81 Virginis, Struve 1764, Struve 1775, 84 Virginis, Struve 1788 (Virgo)

Notable carbon star for May: SS Virginis

One hundred and sixty-five deep-sky objects for May: NGC 5248 (Bootes); M3, M51, M63, M94, M106, NGC 4111, NGC 4138, NGC 4143, NGC 4151, NGC 4214, NGC 4217, NGC 4244, NGC 4346, NGC 4369, NGC 4449, NGC 4485, NGC 4490, NGC 4618, NGC 4631, NGC 4656, NGC 4868, NGC 5005, NGC 5033, NGC 5297, NGC 5353, NGC 5354, Up 1 (Canes Venatici); Mel 111, M53, M64, M85, M88, M91, M98, M99, M100, NGC 4064, NGC 4150, NGC 4203, NGC 4212, NGC 4251, NGC 4274, NGC 4278, NGC 4293, NGC 4298, NGC 4302, NGC 4314, NGC 4350, NGC 4414, NGC 4419, NGC 4448, NGC 4450, NGC 4459, NGC 4473, NGC 4474, NGC 4494, NGC 4559, NGC 4565, NGC 4651, NGC 4689, NGC 4710, NGC 4725, NGC 4874, NGC 5053 (Coma Berenices); NGC 4027, NGC 4038-9, NGC 4361 (Corvus); M68, M83, NGC 4105, NGC 4106, NGC 5061, NGC 5101, NGC 5135 (Hydra); M40, NGC 4036, NGC 4041, NGC 4051, NGC 4062, NGC 4085, NGC 4088, NGC 4096, NGC 4100, NGC 4144, NGC 4157, NGC 4605, NGC 5308, NGC 5322 (Ursa Major); M49, M58, M59, M60, M61, M84, M86, M87, M89, M90, M104, NGC 4030, NGC 4073, NGC 4168, NGC 4179, NGC 4206, NGC 4215, NGC 4216, NGC 4224, NGC 4235, NGC 4260, NGC 4261, NGC 4267, NGC 4281, NGC 4339, NGC 4343, NGC 4365, NGC 4371, NGC 4378, NGC 4380, NGC 4387, NGC 4388, NGC 4402, NGC 4429, NGC 4435, NGC 4438, NGC 4517, NGC 4526, NGC 4535, NGC 4536, NGC 4546, NGC 4550, NGC 4551, NGC 4567, NGC 4568, NGC 4570, NGC 4593, NGC 4596, NGC 4636, NGC 4638, NGC 4639, NGC 4643, NGC 4654, NGC 4666, NGC 4697, NGC 4698, NGC 4699, NGC 4753, NGC 4754, NGC 4760, NGC 4762, NGC 4866, NGC 4900, NGC 4958, NGC 5044, NGC 5054, NGC 5068, NGC 5077, NGC 5084, NGC 5087, NGC 5147, NGC 5170, NGC 5247, NGC 5363, NGC 5364 (Virgo)

Top ten deep-sky objects for May: M3, M51, M63, M64, M83, M87, M104, M106, NGC 4449, NGC 4565

Top ten deep-sky binocular objects for May: M3, M51, M63, M64, M84, M86, M87, M104, M106, Mel 111

Challenge deep-sky object for May: 3C 273 (Virgo)

The objects listed above are located between 12:00 and 14:00 hours of right ascension.


Chance favors the prepared mind.

A man is a small thing, and the night is very large and full of wonders.

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