The Solar System in December 2015

Dates and times shown are NZDT (UT + 13 Hours) unless otherwise stated. Rise and set times are for Wellington. They will vary by a few minutes elsewhere in NZ. The southern summer solstice occurs on December 22 at 5.48 pm NZDT (04:48 UT) SUNRISE, SUNSET and TWILIGHT TIMES in December

                    December  1  NZDT                December 31  NZDT
                    morning  evening                 morning  evening
       SUN: rise:   5.40am,  set:  8.39pm    rise:   5.47am,  set:  8.59pm
Twilights
  Civil:    starts: 5.10am,  ends: 9.10pm    starts: 5.16am,  ends: 9.31pm
  Nautical: starts: 4.28am,  ends: 9.51pm    starts: 4.33am,  ends:10.14pm 
  Astro:    starts: 3.40am,  ends:10.40pm    starts: 3.42am,  ends:11.05pm

December PHASES OF THE MOON (times as shown by GUIDE)

  Last quarter:  December  3 at  8.40 pm (07:40 UT)
  New moon:      December 11 at 11.29 pm (10:29 UT)
  First quarter: December 19 at  4.14 am (Dec 18, 15:14 UT) 
  Full moon:     December 26 at 12.12 am (Dec 25, 11:12 UT)

The Planets in December

Only Mercury will be an evening object during December and it will be difficult to see. The remaining naked eye planets will be spread across the morning sky. Saturn too close to the Sun for observation early in the month, all 4 spread widely across the easterly morning sky at the end of December.

Mercury, an evening object, will set some 40 minutes after the Sun on the 1st, only 10 minutes after the end of civil twilight. As a result it will be too low to observed despite a -0.8 magnitude The planet moves rather further from the Sun during December until it reaches its greatest elongation 20° east of the Sun on the 29th. Even then it will set only 75 minutes after the Sun at the end of Nautical twilight. 45 minutes after sunset, Mercury will be only 4.5° above a level horizon towards the west-north-west, so still not an easy object despite its -0.4 magnitude.

Venus, MARS, JUPITER and SATURN in the morning sky during December.

Saturn was at conjunction on the last day of November, so will be too close to the Sun to see during the early part of December.

On the 1st as seen at 5am, the other three planets will be spread out across the evening sky. Most obvious will be Venus, due east and just on 13° up. Mars, magnitude 1.5, will be 14° away to its upper left with an altitude 20°. Jupiter will be 20° beyond Mars and nearly 27° up. Mars and Venus will be in Virgo with the latter 4° below Spica. Jupiter will be in Leo.

During December all three planets will be moving to the east through the stars, Venus most rapidly and Jupiter the slowest. As a result they will spread further apart. Venus will be in Libra by the 12th while Mars will pass Spica on the 24th some 3.5° below the star. Jupiter will remain in Leo but be close to the constellation’s boundary with Virgo by the end of the month. Saturn, in Ophiuchus, will move further into the morning sky to become visible by the end of December.

On the morning of the 31st the 4 planets, from Saturn, through Venus and Mars to Jupiter will be spread across some 77° of sky. Added to that, the Moon, 74% lit, will be 13° beyond Jupiter making a spread of a full 90° in all. At 5am with the Sun just over 8° below the horizon (at Wellington), Venus will be 15.5° up and in a direction 10° south of east. Saturn at magnitude 0.5, will be some 9° up just over 10° to the lower right of Venus. Mars will be on the opposite side of Venus 33° away and 33° above the horizon. Jupiter will be another 35° beyond Mars and 41° above the horizon. Finally the moon will be another 13° beyond Jupiter but at the same altitude.

Earlier in the month, the moon passes the planets. On the morning of December 5 the moon, 37% lit, will be 5.5° from Jupiter, 2 mornings later the moon now 20% lit will be 7° from Mars and the next morning, the 8th, just over 1° from Venus.

Outer Planets

Uranus remains in Pisces during December at magnitude 5.7. It is an evening object. By the end of December it will be setting about 1.30 am.

Neptune is also an evening object throughout December, by the end of December it will set at midnight. The planet is in Aquarius, magnitude 7.9 throughout the month.

Pluto continues to be in Sagittarius throughout December at magnitude 14.4. At the end of the month it sets a few minutes after the Sun.

BRIGHTER ASTEROIDS: (1) Ceres is in Capricornus during December with a magnitude 9.3. It is about 20° from Neptune and like the planet will set close to midnight at the end of December.

(4) Vesta is in Cetus during December although it crosses a corner of Pisces mid month. Its magnitude fades from 7.5 to 8.0 during December. Vesta will be about 15° from Uranus, and will set at a similar time to the planet.

(15) Eunomia starts December in Pegasus but moves into Pisces on the 23rd. Its magnitude fades from 8.9 to 9.4 during December. It is an evening object, by the end of December it will set just after midnight.

(27) Euterpe is in Gemini, it starts December at magnitude 9.4, its brightness peaks at magnitude 8.4 when at opposition on December 25 and drops back to 8.9 by December 31. Euterpe is close to two red stars during the month. On December 14, with a magnitude 8.9, it will be half a degree below mu Gem, mag 2.9. Eight nights later Euterpe, at 8.6, will be 43 arc minutes below eta Gem, mag 3.3. In both instances it will be the brightest object immediately below the star.

Brian Loader  
New Zealand