August 2021 Celestial Calendar

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Dave Mitsky
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August 2021 Celestial Calendar

Post by Dave Mitsky »

August Celestial Calendar by Dave Mitsky

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

8/1 The Moon is 1.7 degrees south-southeast of Uranus at 3:00; a double Galilean shadow transit begins at 10:08; Mercury is in superior conjunction with the Sun (1.342 astronomical units from the Earth, latitude 6.9 degrees) at 14:00; the Curtiss Cross, an X-shaped clair-obscur illumination effect located between the craters Parry and Gambart, is predicted to be visible at 22:20
8/2 Saturn (magnitude +0. 2, apparent size 18.6") is at opposition at 6:00; the Moon is at apogee, subtending 29' 33" at a distance of 404,409 kilometers (251,289 miles) at 7:35; the Moon is 4.8 degrees southeast of the bright open cluster M45 (the Pleiades or Subaru) in Taurus at 11:00
8/3 The Moon is at the ascending node (longitude 68.9 degrees) at 3:00; the Moon is 5.6 degrees north of the first-magnitude star Aldebaran (Alpha Tauri) at 5:00; Mercury is at its northernmost latitude from the ecliptic plane (7.0 degrees) at 6:00
8/5 The Moon is 1.1 degrees north of the bright open cluster M35 in Gemini at 2:00; asteroid 4 Juno (magnitude +10.8) is stationary in Ophiuchus at 4:00
8/6 The Moon is 6.7 degrees south of the first-magnitude star Castor (Alpha Geminorum) at 15:00; the Moon is 3.1 degrees south of the first-magnitude star Pollux (Beta Geminorum) at 20:00
8/7 The astronomical cross-quarter day known as Lammas or Lughnasadh, the midpoint between the summer solstice and the autumnal equinox, occurs today; the Moon is 3.0 degrees north-northeast of the bright open cluster M44 (the Beehive Cluster or Praesepe) in Cancer at 22:00
8/8 A double Galilean shadow transit begins at 12:42; New Moon (lunation 1220) occurs at 13:50
8/9 The Moon is 3.2 degrees north-northeast of Mercury at 6:00; the Moon is 4.5 degrees north-northeast of the first-magnitude star Regulus (Alpha Leonis) at 16:00
8/10 The Moon is 4.0 degrees north-northeast of Mars at 4:00; the Sun enters the constellation of Leo, at longitude 138.2 degrees on the ecliptic, at 15:00
8/11 The Moon is 3.9 degrees north-northeast of Venus at 11:00
8/12 Mercury is 1.1 degrees north-northeast of Regulus at 1:00; the peak of the Perseid meteor shower (a zenithal hourly rate of 100 or more per hour) is predicted to occur at 19:00; asteroid 349 Demboska (magnitude +9.8) is at opposition in Piscis Austrinus at 21:34
8/13 The Moon is 5.5 degrees north-northeast of the first-magnitude star Spica (Alpha Virginis) at 15:00
8/15 The Lunar X, also known as the Werner or Purbach Cross, an X-shaped clair-obscur illumination effect involving various ridges and crater rims located between the craters La Caille, Blanchinus, and Purbach, is predicted to be visible at 10:28; a double Galilean shadow transit begins at 14:41; a double Galilean shadow transit begins at 15:17; First Quarter Moon occurs at 15:20; a triple Galilean satellite transit occurs at 15:31
8/16 Mars and Neptune are at heliocentric opposition (longitudes 171.6 degrees and 351.6 degrees) at 13:00; the Moon is at the descending node (longitude 247.6 degrees) at 16:00; the Moon is 4.4 degrees north-northeast of the first-magnitude star Antares (Alpha Scorpii) at 22:00
8/17 The Moon is at perigee, subtending 32' 22'' from a distance of 369,125 kilometers (229,363 miles), at 9:16
8/19 Mercury is 0.1 degrees south of Mars at 4:00; asteroid 43 Ariadne is at opposition (magnitude +9.6) in Aquarius at 19:10
8/20 Uranus is stationary, with retrograde motion to begin, at 0:00; Jupiter is at opposition (magnitude -2.9, apparent size 49.1") at 0:00
8/21 The Moon is 3.6 degrees south of Saturn at 0:00
8/22 The Moon is 3.7 degrees southeast of Jupiter at 8:00; Full Moon (known as the Fruit, Grain, Green Corn, or Sturgeon Moon) occurs at 12:02; a double Galilean shadow transit begins at 18:42; the Sun's longitude is 150 degrees at 22:00
8/24 The Moon is 3.7 degrees southeast of Neptune at 6:00; asteroid 89 Julia (magnitude +9.0) is at opposition in Aquarius at 14:22
8/25 The Martian northern hemisphere summer solstice occurs at 0:00
8/26 Mercury is at the descending node through the ecliptic plane at 15:00
8/28 The Moon is 1.4 degrees southeast of Uranus at 11:00
8/29 Venus is at the descending node through the ecliptic plane at 5:00; the Moon is 4.6 degrees southeast of M44 at 19:00; a double Galilean shadow transit begins at 22:43
8/30 The Moon is at apogee, subtending 29' 34" at a distance of 404,098 kilometers (251,096 miles) at 2:22; the Moon is at the ascending node (longitude 66.2 degrees) at 5:00; Last Quarter Moon occurs at 7:13; the Moon is 5.8 degrees north-northwest of Aldebaran at 13:00
8/31 The Curtiss Cross is predicted to be visible at 9:42

John Flamsteed, Christian Mayer, Pierre François André Méchain, Maria Mitchell, and Otto Struve were born this month.

The gibbous phase of Mars was first observed by Francesco Fontana on August 24, 1638. Abraham Ihle discovered the globular cluster M22 on August 26, 1665. Nicolas Sarabat discovered Comet C/1729 P1 (Sarabat) on August 1, 1729. Caroline Herschel discovered Comet C/1786 P1 (Herschel) on August 1, 1786. The Saturnian satellite Enceladus was discovered by William Herschel on August 28, 1789. Dominique Dumouchel was the first person to observe the return of Comet 1P/Halley on August 5, 1835. John Russell Hind discovered asteroid 7 Iris on August 13, 1847. Asaph Hall discovered Deimos on August 11, 1877 and Phobos on August 17, 1877. The first extragalactic supernova, S Andromedae, was discovered by Ernst Hartwig on August 20, 1885. David Jewitt and Jane Luu discovered the trans-Neptunian object (15760) 1992 QB1 on August 30, 1992. The Jovian satellite 2002 Laomedeia was discovered by Matthew Holman on August 13th, 2002.

The peak of the Perseid meteor shower takes place on the night of August 11th/August 12th and is not compromised by moonlight. The periodic comet 109P/Swift-Tuttle is the source of Perseid meteors. The shower’s radiant lies just to the southeast of the Double Cluster (NGC 869 and NGC 884). For more on this year’s Perseids, see page 52 to page 55 of the August 2021 issue of Astronomy and page 48 of the August 2021 issue of Sky & Telescope or click on ... eor-shower and ... r-in-2021/

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

The Moon is 21.8 days old, is illuminated 47.4%, subtends 29.5 arc minutes, and is located in Aries on August 1st at 00:00 UT. The Moon is at its greatest northern declination on August 6th (+25.6 degrees) and its greatest southern declination on August 19th (-25.8 degrees). Longitudinal libration is at a maximum of +5.4 degrees on August 24th and a minimum of -4.9 degrees on August 9th. Latitudinal libration is at a maximum of +6.6 degrees on August 23rd and a minimum of -6.6 degrees on August 10th. Favorable librations for the following lunar features occur on the indicated dates: Crater Piazzi on August 4th, Crater Hayn on August 19th, Crater Compton on August 21st, and Crater Boss F on August 22th. The Moon is at apogee (at a distance 63.41 Earth-radii) on August 2nd and again (at a distance 63.26 Earth-radii) on August 30th and at perigee (at a distance of 57.87 Earth-radii) on August 17th. New Moon (i.e., the dark of the Moon) occurs on August 8th. Full Moon, a Blue Moon by the classic definition of the third Full Moon in a summer that has four, occurs on August 22nd. Browse for information on 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. Click on for an excellent online lunar map. Visit to download the free Virtual Moon Atlas. Consult for current information on the Moon and ... rform.html for information on various lunar features. 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 Cancer on August 1st. It enters the constellation of Leo on August 10th and achieves an ecliptic longitude of 150 degrees on August 21st.

Brightness, apparent size, illumination, distance from the Earth in astronomical units, and location data for the planets and Pluto on August 1: Mercury (magnitude -2.1, 5.0", 100% illuminated, 1.34 a.u., Cancer), Venus (magnitude -3.9, 12.7", 82% illuminated, 1.32 a.u., Leo), Mars (magnitude +1.8, 3.7", 99% illuminated, 2.56 a.u., Leo), Jupiter (magnitude -2.8, 48.5", 100% illuminated, 4.07 a.u., Aquarius), Saturn (magnitude +0.2, 18.6", 100% illuminated, 8.94 a.u., Capricornus), Uranus (magnitude +5.7, 3.6", 100% illuminated, 19.57 a.u. on August 16th, Aries), Neptune (magnitude +7.8, 2.4", 100% illuminated, 29.04 a.u. on August 16th, Aquarius), and Pluto (magnitude +14.3, 0.1", 100% illuminated, 33.45 a.u. on August 16th, Sagittarius).

This month Mercury, Venus, and Mars are located in the west, Jupiter and Neptune in the east, and Saturn in the southeast during the evening. At midnight, Jupiter and Saturn can be found in the south, Uranus in the east, and Neptune in the southeast. Uranus is in the southeast, and Jupiter, Saturn, and Neptune in the southwest in the morning sky.

Mercury is in superior conjunction on August 1st and is at its greatest heliocentric latitude north on August 3rd. Mercury and Mars are in close conjunction on the evening of August 18th (August 19th UT), with a separation of just seven arc minutes. The speediest planet will be at the descending node on August 26th. Mercury will become visible again in the evening sky towards the end of the month but it will be the worst evening apparition of 2021 for mid-northern hemisphere observers.

During August, Venus changes little in brightness but increases in angular size from 12.7 arc seconds to 15.0 arc seconds, while it drops in illumination from 82% to 73%. Venus continues its descent, despite increasing in solar elongation from 33 to 40 degrees, crossing the celestial equator on August 17th. A slender waxing crescent Moon passes four degrees to the north of the planet on August 11th.

Mars may be visible with difficulty in early August. Mars sets about an hour after the Sun. Its elongation from the Sun drops from 22 to 12 degrees this month. A slender waxing crescent Moon passes about four degrees north of Mars on the evening of August 9th (August 10th UT), which may be the last time that the Red Planet is visible until the end of the year. Mars and Neptune are at heliocentric opposition on August 16th. Mars and Mercury are in conjunction on August 18th-August 19th. Mars shines at magnitude +1.8 and subtends only 3.6 arc seconds as August comes to an end.

Jupiter changes only slightly in brightness and apparent size this month. It reaches opposition on August 20th. On that date, Jupiter is 14 degrees south of the celestial equator in eastern Capricornus, is 33 light minutes from the Earth, and subtends 49.1 arc seconds. The Full Moon passes four degrees to the south of Jupiter on August 22nd. An article on observing Jupiter can be found on pages 40 to 45 of the August 2021 issue of Astronomy. An article on observing Jupiter and Saturn appears on pages 49 and 50 of the August 2021 issue of Sky & Telescope. From 2:42 to 5:07 UT on the night of August 11th/August 12th, just one of Jupiter's satellites, namely Callisto, is visible. Callisto is located 10 arc minutes due east of the planet, while Io and Ganymede are behind it and Europa and its shadow are transiting across Jupiter's disk. In just six minutes, from 5:07 to 5:13 UT, Ganymede, Io, and Europa respectively reappear from occultation. Double Galilean satellite shadow transits occur on August 1st, August 8th, August 15th, August 22nd, and August 29th. Two shadow transits and a triple satellite transit, that is best seen from Asia and Australasia, take place on August 15th. Information on Great Red Spot transit times and Galilean satellite events is available on pages 50 and 51 of the August 2021 issue of Sky & Telescope and online at ... ing-tools/ and

When Saturn achieves opposition on August 2nd, it is 18 degrees south of the celestial equator and is 74 light minutes from the Earth. At that time, the planet's disk subtends 18.6 arc seconds and its rings span almost 42 arc seconds and are inclined by 18 degrees. On August 20th, the waxing gibbous Moon passes four degrees to the south of Saturn. Titan is positioned north of Saturn on August 3rd and August 19th and south of it on August 11th and August 26th/27th. Saturn's peculiar satellite Iapetus shines faintly at almost 12th magnitude as it reaches eastern elongation almost nine arc minutes east of the planet on August 12th. It reaches inferior conjunction 50 arc seconds from Saturn on August 31st. For information on Saturn’s satellites, browse ... ing-tools/

Uranus is located in southern Aries. It forms an equilateral triangle with Omicron Arietis (magnitude +5.8) and Sigma Arietis (magnitude +5.5). The waning gibbous Moon passes three degrees southeast of Uranus on the night of August 10th/August 11th. Uranus reaches its first stationary point on August 20th. The seventh planet achieves its highest declination (almost 16 degrees) since the 1960s this month. Visit for a finder chart. The positions of the planet's brightest satellites can be determined using the interactive observing tool at ... -ofuranus/

Neptune can be found in eastern Aquarius about five degrees east of the fourth-magnitude star Phi Aquarii. Mars and Neptune are at heliocentric conjunction on August 16th. The waning gibbous Moon passes less than four degrees southeast of Neptune on August 24th. Browse for a finder chart. Triton, Neptune's brightest satellite, can be located using the interactive observing tool at ... n-tracker/

The dwarf planet Pluto is located in eastern Sagittarius about 10 degrees northeast of the third-magnitude star Tau Sagittarii. Finder charts can be found at pages 48 and 49 of the July 2021 issue of Sky & Telescope and on page 243 of the RASC Observer’s Handbook 2021.

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

The periodic comet 4P/Faye heads eastward through Taurus during August. This comet has a period of 7.6 years and shines at approximately tenth magnitude as it passes just south of the faint nebula NGC 1554/5 on August 21st and into the border of the bright open cluster NGC 1647 on August 30th. Visit and and for information on comets visible this month.

Asteroid 89 Julia shines at ninth magnitude as it travels northwestward through Aquarius this month, passing about one degree south of Gamma Aquarii on August 6th and just south of Sadalmelik (Alpha Aquarii) on August 21st. It reaches opposition on August 24th. Other asteroids brighter than magnitude +11.0 reaching opposition include 43 Ariadne, 80 Sappho, and 349 Dembowska. For information on asteroid occultations taking place this month, see

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 this month can be downloaded at and ... Star-Chart

Data on current supernovae can be found at

Finder charts for the Messier objects and other deep-sky objects are posted at and and ... -september

Telrad finder charts for the Messier Catalog are posted at

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

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

Author Phil Harrington offers an excellent freeware planetarium program for binocular observers known as TUBA (Touring the Universe through Binoculars Atlas), which also includes information on purchasing binoculars, at

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

Sixty binary and multiple stars for August: 5 Aquilae, Struve 2404, 11 Aquilae, Struve 2426, 15 Aquilae, Struve 2449, 23 Aquilae, Struve 2532, Pi Aquilae, 57 Aquilae (Aquila); Beta Cygni (Albireo), 16 Cygni, Delta Cygni, 17 Cygni (Cygnus); 41 & 40 Draconis, 39 Draconis, Struve 2348, Sigma Draconis, Struve 2573, Epsilon Draconis (Draco); 95 Herculis, 100 Herculis, Struve 2289, Struve 2411 (Hercules); Struve 2349, Struve 2372, Epsilon-1 & Epsilon-2 Lyrae (the Double-Double), Zeta-2 Lyrae, Beta Lyrae, Otto Struve 525, Struve 2470 & Struve 2474 (the Other Double-Double) (Lyra); 67 Ophiuchi, 69 Ophiuchi, 70 Ophiuchi, Struve 2276, 74 Ophiuchi (Ophiuchus); Mu Sagittarii, Eta Sagittarii, 21 Sagittarii, Zeta Sagittarii, H N 119, 52 Sagittarii, 54 Sagittarii (Sagittarius); Struve 2306, Delta Scuti, Struve 2373 (Scutum); Struve 2296, Struve 2303, 59 Serpentis, Theta Serpentis (Serpens Cauda); Struve 2445, Struve 2455, Struve 2457, 4 Vupeculae, Struve 2521, Struve 2523, Struve 2540, Struve 2586, Otto Struve 388, Struve 2599 (Vulpecula)

Notable carbon star for August: V Aquilae

Eighty deep-sky objects for August: B139, B142, B143, NGC 6709, NGC 6738, NGC 6741, NGC 6751, NGC 6755, NGC 6772, NGC 6778, NGC 6781, NGC 6804, PK64+5.1 (Aquila); NGC 6819, NGC 6826, NGC 6834, (Cygnus); NGC 6643, NGC 6742 (Draco); DoDz 9 (Hercules); M56, M57, NGC 6703, NGC 6791, Ste1 (Lyra); NGC 6572, NGC 6633 (Ophiuchus); H20, M71 (Sagitta); B86, B87, B90, B92, B93, M8, M17, M18, M20, M21, M22, M23, M24, M25, M28, M54, M55, M69, M70, M75, NGC 6520, NGC 6544, NGC 6546, NGC 6553, NGC 6565, NGC 6603, NGC 6818, NGC 6822 (Sagittarius); IC 4703, IC 4756, M16, NGC 6604 (Serpens Cauda); B100, B101, B103, B104, B110, B111, B113, Bas 1, IC 1295, M11, M26, NGC 6649, NGC 6712 (Scutum); Cr 399 (asterism), M27, NGC 6802, NGC 6823, NGC 6834, NGC 6940, St 1 (Vulpecula)

Top ten binocular deep-sky objects for August: Cr 399, IC 4756, M8, M11, M17, M22, M24, M25, M27, NGC 6633 (IC 4756 and NGC 6633 are collectively known as the Binocular Double Cluster)

Top ten deep-sky objects for August: M8, M11, M16, M17, M20, M22, M24, M27, M55, M57

Challenge deep-sky object for August: Abell 53 (Aquila)

The objects listed above are located between 18:00 and 20:00 hours of right ascension.
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