Astronomical Diary
Calendar of Astronomical Events DECEMBER 2021
Date Event Time
02 Pheonicid Meteor Shower (ZHR = var) 08:00 PM
06 December φ-Cassiopeid Meteor Shower (ZHR = var) 09:00 PM
07 Puppid-Velid Meteor Shower (ZHR = 10) 03:00 AM
07 Moon passing 1°52' S of Venus 08:49 AM
08 Venus at greatest brightness 12:09 AM
08 Moon passing 4°11' S of Saturn 09:49 AM
09 Monocerotid Meteor Shower (ZHR = 2) 01:00 AM
09 Moon passing 4°28' S of Jupiter 02:10 PM
12 σ-Hydrid Meteor Shower (ZHR = 3) 03:00 AM
14 Geminid Meteor Shower (ZHR = 120) 02:00 AM
16 Comae Berenicid Meteor Shower (ZHR = 3) before dawn
19 December Leonis Minorid Meteor Shower (ZHR = 5) 05:00 AM
21 December Solstice 11:59 PM
22 Ursid Meteor Shower (ZHR = 10) before dawn
Moon Phases
New Moon
Dec 04 03:43 PM
First Quarter
Dec 11 09:36 AM
Full Moon
Dec 19 12:35 PM
Last Quarter
Dec 27 10:24 AM
Rise and Set Times of Planets
Date Mercury Venus Mars Jupiter Saturn
Rise Set Rise Set Rise Set Rise Set Rise Set
Dec 01 06:11 AM 05:27 PM 09:11 AM 08:21 PM 04:49 AM 04:15 PM 11:20 AM 10:53 PM 10:20 AM 09:42 PM
Dec 11 06:43 AM 05:53 PM 08:49 AM 08:02 PM 04:40 AM 04:01 PM 10:46 AM 10:20 PM 09:44 AM 09:07 PM
Dec 21 07:13 AM 06:23 PM 08:11 AM 07:29 PM 04:31 AM 03:50 PM 10:12 AM 09:48 PM 09:08 AM 08:32 PM
Dec 31 07:37 AM 06:53 PM 07:16 AM 06:38 PM 04:23 AM 03:39 PM 09:39 AM 09:16 PM 08:32 AM 07:57 PM

* = following day

Stars and Constellation

For the whole month of December, the summer constellations can still be observed in the western sky for the first few hours after sunset. The Summer Triangle asterism is still located fairly high in the sky during the first half of the month, with Vega of the constellation Lyra heading west-northwest, Deneb of the constellation Cygnus closest to the zenith, and Altair of the constellation Aquila is heading west southwest (Figures 1a and 1b). The Summer Triangle continues to dive westward and can be observed lying low near the western horizon in late December as seen from Figure 1c [1].

Figure 1: The view of the night sky at 06:00 P.M. on several days of December 2021 using the Stellarium Application.

Fig1a
Figure 1a. December 1, 2021

Fig1b
Figure 1b. December 15, 2021

Fig1c
Figure 1c. December 30, 2021

The members of the autumn constellations can be notably observed as it gets high in the eastern sky. The view of the observable constellations after sunset in mid-December is shown in Figure 2.

Fig2
Figure 2. The view of the sky after sunset on mid-December 2021 using the Stellarium application

Cassiopeia, a “W” shaped constellation is going to be very prominent and can be easily seen in the sky due to its unique formation and high position in the north-northwestern sky. When the Big Dipper asterism is not visible in the night sky, Cassiopeia may be used as an alternative to and the position of the north star, Polaris. However, when compared to using the Big Dipper, the result achieved using this method may not be as accurate. The star positioned in the middle of the constellation Cassiopeia can be utilized as a pointer star to lead to the approximate position of Polaris, as shown in Figure 3 [1].

Fig3
Figure 3. The view of the northern sky on mid-December 2021 at 09:00 P.M. showing how to locate the position of the north star Polaris using the constellation Cassiopeia using the Stellarium application

Planetary Location

For the whole month of December, Venus can be observed in the southwestern part of the sky after sunset, however, in late December, Venus may be already difficult to observe as it is just a few degrees above the horizon. Jupiter and Saturn can also be observed in the southwestern portion of the sky after sunset.

Fig4
Figure 4. The view of the southwestern sky after sunset on 07 December 2021 showing the Moon-Venus Conjunction using the Stellarium application

The thin crescent Moon will pass 1°52' S of Venus on 07 December 2021 at 08:49 A.M. The exact moment of the Moon-Venus Conjunction cannot be observed since it will occur during the day. However, the close pairing will be visible after sunset at around 05:41 P.M. (Figure 4) at an altitude of 30°above the southwestern horizon. The close pairing may be observed until 08:13 P.M. as the pair sinks towards the horizon. By then, the Moon and Venus will be at mag -10.4 and mag -4.7 and are located both in the constellation Sagittarius [2].

On 08 December 2021 at 12:09 A.M., Venus will reach its greatest brightness at mag -4.7 [3].

On 08 December 2021, at 09:49 A.M., the 4-day old Moon will pass 4°11' S of Saturn Again, the exact instance of the crescent Moon-Saturn Conjunction will not be observed as it will occur during the day. However, the view of the conjunction may still be enjoyed after sunset around 05:42 P.M. as the Moon and Saturn will be observed 44° above the southwestern horizon (Figure 5) until the pair sets at around 09:17 P.M. [4]. The Moon and Saturn will be at mag -11.0 and mag 0.5, respectively, and will be both located in the constellation Capricornus [4].

Fig5
Figure 5. The view of the southwestern sky after sunset on 08 December 2021 showing the Moon-Saturn Conjunction using the Stellarium application

On 09 December 2021, the Moon will be passing 4°28' S of Jupiter at around 02:10 P.M. The close pairing will be visible after sunset at around 05:42 P.M. at about 57° above the southwestern horizon (Figure 6). The Moon and Jupiter will be at mag -11.5 and mag -2.3, respectively, and will be both located in the constellation Capricornus [5].

These Moon-planetary conjunctions can be seen through the naked eye or using a pair of binoculars. Please do note that the separation of the above-mentioned conjunctions is too wide to fit in the field of view of a telescope.

Fig6
Figure 6. The view of the southwestern sky after sunset on 09 December 2021 showing the Moon-Jupiter Conjunction using the Stellarium application

Meteor Showers

Several meteor showers can be observed for December. The summary details of the observable meteor showers are presented in Table 1. The first column of the table is the name of the meteor shower, which is usually derived from the constellation where the shower's radiant is located. The radiant of the shower, listed in the second column, is a point in the sky where meteors seem to originate. The position of the meteor shower radiants (enclosed in the green solid circle) of the observable meteor showers for December 2021 during its highest position is presented as follows: Pheonicids (Figure 7), December φ Cassiopeids (Figure 8), Puppid-Velids (Figure 9), Monocerotids (Figure 10), σ-Hydrids (Figure 11), Geminids (Figure 12), Comae Berenicids (Figure 13), December Leonis Minorids (Figure 14), and Ursids (Figure 15).
Meteor Shower Name Radiant Active Date Peak Date Best Viewed Time ZHR Lunar Phase
Pheonicids Phoenix 28 Nov - 09 Dec 02 Dec 08:00 P.M. var Waxing Crescent
December φ Cassiopeids Andromeda 01 - 08 Dec 06 Dec 09:00 P.M. var Waxing Crescent
Puppid-Velids Vela 01 - 15 Dec 07 Dec 03:00 A.M. 10 Waxing Crescent
Monocerotids Monoceros 05 - 20 Dec 09 Dec 01:00 A.M. 2 Waxing Crescent
σ-Hydrids Hydra 03 - 15 Dec 12 Dec 03:00 A.M. 3 Waxing Gibbous
Geminids Gemini 04 - 17 Dec 14 Dec 02:00 A.M. 120 Waxing Gibbous
Comae Berenicids Leo 12 - 23 Dec 16 Dec before dawn 3 Waxing Gibbous
December Leonis Minorids Leo Minor 05 Dec - 04 Feb 19 Dec 05:00 A.M. 5 Full Moon
Ursids Ursa Minor 17 - 26 Dec 22 Dec before dawn 10 Waning Gibbous

The third column shows the period when the meteor shower is active and can be observed while the Peak Date as shown in the fourth column indicates the point in time when the greatest number of meteors can be observed. The Best viewed time, listed in the fifth column, represents the time when the radiant point is at its highest point in the sky. The Zenithal Hourly Rate (ZHR), listed in the sixth column, indicates the number of meteors an observer can see in an hour during the peak activity. However, the computation of ZHR assumes that one is observing in a perfectly dark and clear sky and the radiant is located directly overhead. The number of ZHR decreases under certain circumstances. The last column shows the phase of the Moon during the peak date of the shower. Unfortunately, the waxing gibbous phase of the Moon during the peak of Geminids and Comae Berenicids, the Full Moon phase during the peak of December Leonis Minorids, and the waning gibbous phase of the Moon during Ursids will produce a significant interference in the meteor shower observation throughout the night.

Meteor showers are can be observed through the naked eyed and there is no need to use special equipment such as telescopes or binoculars. To maximize the viewing experience, it is ideal to observe in a dark site away from the city lights under clear and moonless sky conditions.

*(Click image to enlarge view)

Fig7
Figure 7. The view of the sky during the peak of Pheonicids on 02 December 2021 at 08:00 P.M.

Fig8
Figure 8. The view of the sky during the peak of December φ Cassiopeids on 06 December 2021 at 09:00 P.M.

Fig9
Figure 9. The view of the sky during the peak of Puppid-Velids on 07 December 2021 at 03:00 A.M.
Fig10
Figure 10. The view of the sky during the peak of Monocerotids on 09 December 2021 at 01:00 A.M.
Fig11
Figure 11. The view of the sky during the peak of σ-Hydrids on 12 December 2021 at 03:00 A.M.
Fig12
Figure 12. The view of the sky during the peak of Geminids on 14 December 2021 at 02:00 A.M.
Fig13
Figure 13. The view of the sky during the peak of Comae Berenicids on 16 December 2021 at 02:00 A.M.
Fig14
Figure 14. The view of the sky during the peak of December Leonis Minorids on 19 December 2021 at 05:00 A.M.
Fig15
Figure 15. The view of the sky during the peak of Ursids on 22 December 2021 at 02:00 A.M.

Total Solar Eclipse

On 04 December 2021 from 01:29 P.M. to 05:36 P.M., the Moon will be passing in front of the Sun, thus, creating a rare astronomical phenomenon called Total Solar Eclipse. Unfortunately, the Total Solar Eclipse will only be visible in Antarctica and not in the Philippines [6].

Comet: the Distant Visitors

On the 12th of December 2021, another comet named C/2021 A1 (Leonard) will make its closest approach to the Earth at a distance of 0.23 AU. The comet, however, will not be visible during its perigee since it will be below the horizon after sunset. Luckily, there are other chances to see the comet on a different day of the month. The position of Comet C/2021 A1 (Leonard) every other night for the whole month of December 2021 is shown in Table 2 [7].
Date Constellation Observable Time Highest Position in the Sky
01 Dec Canes Venatici 03:42 A.M. - 05:09 A.M. 37° above NE horizon (at 05:09 A.M.)
03 Dec Bootes 03:57 A.M. - 05:10 A.M. 34° above NE horizon (at 05:10 A.M.)
05 Dec Bootes 04:15 A.M. - 05:11 A.M. 29° above NE horizon (at 05:11 A.M.)
07 Dec Bootes 04:50 A.M. - 05:13 A.M. 23° above NE horizon (at 05:13 A.M.)
09 Dec Serpens Caput Not observable
11 Dec Ophiuchus Not observable
13 Dec Serpens Cauda Not observable
15 Dec Sagittarius Not observable
17 Dec Sagittarius Not observable
19 Dec Sagittarius Not observable
21 Dec Microscopium 06:28 P.M. - 06:33 P.M. 18° above SW horizon (at 06:28 P.M.)
23 Dec Microscopium 06:30 P.M. - 06:42 P.M. 19° above SW horizon (at 06:30 P.M.)
25 Dec Microscopium 06:28 P.M. - 06:42 P.M. 20° above SW horizon (at 06:28 P.M.)
27 Dec Microscopium 06:30 P.M. - 06:43 P.M. 20° above SW horizon (at 06:30 P.M.)
29 Dec Piscis Austrinus 06:31 P.M. - 06:39 P.M. 18° above SW horizon (at 06:31 P.M.)
31 Dec Piscis Austrinus 06:33 P.M. - 06:36 P.M. 18° above SW horizon (at 06:33 P.M.)

December Solstice

The December Solstice will be on 21 December 2021 at 11:59 P.M. By then, the Sun will reach its most southerly point in the sky, in the constellation Capricornus, at a declination of 23.5°S. During the December Solstice, the northern hemisphere will experience the shortest day and this day also marks the first day of winter. Consequently, in the southern hemisphere, this day marks the first day of summer [8].

Notes and References

*All times displayed are in Philippine Standard Time (PhST)

References
[1] T. U. of Arizona, \Skywatcher's Guide: December 2020 and January 2021." https://flandrau.org/publication/skywatchers-guide-december-2020-and-january-2021, Last accessed on 2021-11-4, 2021.
[2] D. Ford, \In-The-Sky.org Guide to the night sky: Conjunction of the Moon and Venus." https://in-the-sky.org/news.php?id=20211207_20_100, Last accessed on 2021-11-4, 2021.
[3] D. Ford, \In-The-Sky.org Guide to the night sky: Venus at greatest brightness." https://in-the-sky.org/news.php?id=20211207_11_100, Last accessed on 2021-11-4, 2021.
[4] D. Ford, \In-The-Sky.org Guide to the night sky: Conjunction of the Moon and Saturn." https://in-the-sky.org/news.php?id=20211209_20_100, Last accessed on 2021-11-4, 2021.
[5] D. Ford, \In-The-Sky.org Guide to the night sky: Conjunction of the Moon and Jupiter." https://in-the-sky.org/news.php?id=20211208_20_100, Last accessed on 2021-11-4, 2021.
[6] D. Ford, \In-The-Sky.org Guide to the night sky: Total Solar Eclipse." https://in-the-sky.org/news.php?id=20211204_09_100, Last accessed on 2021-11-10, 2021.
[7] D. Ford, \In-The-Sky.org Guide to the night sky: C/2021 A1 (leonard) at perigee." https://in-the-sky.org/news.php?id=20211212_19_100, Last accessed on 2021-11-10, 2021.
[8] D. Ford, \In-The-Sky.org Guide to the night sky: December Solstice." https://in-the-sky.org/news.php?id=20211221_07_100, Last accessed on 2021-11-10, 2021.

For more information, call or email:

Ms. Ma. Rosario C. Ramos, RCE
Chief, SSAS - RDTD
PAGASA - DOST
Diliman, Quezon City
Trunkline: 8284-0800 loc 116, 107
Email add: astronomyph.pagasa@gmail.com

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