The solar system in September 2015

Dates and times are NZST (UT + 12 hours) unless otherwise specified up to September 26. From September 27 they are NZDT (UT + 13 Hours). NZDT commences on Sunday September 27 at 2am when clocks should be put forward one hour.

Rise and set times are for Wellington. They will vary by a few minutes elsewhere in NZ.

The southern spring equinox is on September 23, with the Sun on the celestial equator at 8:21 pm

Sunrise, sunset and twilight times in September

                     September  1  NZST                 September 30  NZDT
                    morning  evening                 morning  evening
       SUN: rise:   6.44am,  set:  5.58pm    rise:   6.55am,  set:  7.27pm
Twilights
  Civil:    starts: 6.19am,  ends: 6.24pm    starts: 6.30am,  ends: 7.53pm
  Nautical: starts: 5.47am,  ends: 6.56pm    starts: 5.58am,  ends: 8.25pm 
  Astro:    starts: 5.15am,  ends: 7.28pm    starts: 5.24am,  ends: 8.59pm

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

  Last quarter:  September  5 at  9.54 pm (09:54 UT)
  New moon:      September 13 at  6.41 pm (06:41 UT)
  First quarter: September 21 at  8.59 pm (08:59 UT) 
  Full moon:     September 28 at  3.51 pm (02:51 UT)

Eclipses

A partial eclipse of the Sun on September 13 will be visible from southern parts of Africa, the southern half of the Malagasy Republic, the South Indian Ocean and Antarctica. No part of the eclipse is visible from Australia of New Zealand. This is an annular eclipse but the path of annularity misses the Earth.

A total eclipse of the moon on September 28 is also not visible from Australasia. The total phase of the eclipse, lasing some 82 minutes, is best seen from countries either side of the Atlantic Ocean.

The planets in September

Mercury will be well placed for evening viewing during the earlier part of the month. Venus, Mars and Jupiter are all morning objects rising a little before the Sun. Saturn, in the evening sky, will set before midnight. An occultation of Uranus by the moon on the morning of September 2 will be visible from most of NZ.

Mercury is an easy early evening object during the first half of September, setting 2 hours or more after the Sun. On the 1st, 50 minutes after sunset the planet, magnitude 0.2, will be some 15° above the horizon to the west. On the 4th Mercury is at its greatest elongation 27° east of the Sun. For nearly two weeks after that its evening altitude slowly declines as its easterly motion through the stars slow. Then on the 17th the planet is stationary before starting to move back to the west, following a path through the stars close to the one it took in the first part of September.

The return means the distance of Mercury from the Sun rapidly declines in the latter part of September as does its evening altitude so that it slips out of view. Mercury is at inferior conjunction between the Earth and Sun at the very end of the month. The actual conjunction is at about 4 am on the morning of October 1.

Venus was at inferior conjunction mid August, so September find it moving up into the morning sky. It rises nearly 100 minutes before the Sun on September 1. On the 5th Venus is stationary, after which it will start moving east towards the Sun. But the Sun itself will be moving to the east through the stars a little more rapidly. As a result the time Venus rises before the Sun will continue to slowly increase, up to almost 2 hours earlier on the 30th.

Venus starts the month in Cancer. Its easterly motion takes it into Leo on the 24th. Before that on the morning of the 10th the 11% lit crescent moon with be 7° to the left of Venus.

Mars is also a morning object, but rather lower than Venus. It rises just under an hour before the Sun on the 1st and 70 minutes before the Sun on the 30th. Mars will be at magnitude 1.8 all month.

Like Venus, Mars starts the month in Cancer, moving on into Leo on the 6th. In Leo it will move towards Regulus, alpha Leo, and is closest to the magnitude 1.4 star on the morning of September 25, when the two will be about 50 arc-minutes apart. Mars, at magnitude 1.8 will be slightly fainter than Regulus and to the lower left of the star.

The moon, a 6% lit waning crescent, will be just under 4° above Mars on the morning of the 11th, one day after it passes Venus.

Jupiter is the third planet in the morning sky that rises shortly before sunrise. It is in Leo all month, moving away from Regulus. It was at conjunction with the Sun on August 26, so will rise only 3 minutes earlier than the Sun at the beginning of September. By the end of the month this will have increased to nearly an hour before the Sun, but the planet will be only 5° above the horizon twenty minutes before sunrise making it a difficult object to see.

Saturn will be the only naked eye planet left in the evening sky once Mercury has slipped out of it. It sets at 12.40 am at the beginning of September and 11.56 pm (NZDT) on the 30th. Hence it will be readily visible in the earlier part of the evening. It will be in Libra about 12° below Antares all month, Saturn moving slightly closer to Antares as the month progresses.

The moon a 29% broad crescent will be some 3.5° to the right of Saturn on September 19.

Outer planets

Uranus remains in Pisces during September. It rises around 9.14 pm on the 1st and 8.15 pm (NDST) on the 30th. The planet will be at magnitude 5.7 so readily seen in binoculars.

OCCULTATION OF URANUS. On the morning of September 2 an occultation of Uranus by the moon will be visible in NZ for places just north of Auckland southwards. A grazing occultation occurs just south of Wellsford. The disappearance will be at the bright limb of the of the 88% lit moon so difficult to observe. The reappearance at the unlit limb will be a lot easier to see using a small telescope.

Unlike stellar occultations, the occultation of Uranus will not be instantaneous due to the angular diameter of the planet. In the South Island the reappearance will take about 6 seconds, but this time will increase further north, nearer the graze path, to almost 20 seconds at Auckland.

The time of the reappearance is near 5 am; for most places a little before, but for Wellington and places near the east coast of the North Island Uranus will reappear shortly after 5am. Users of Occult will be able to generate accurate times for their position.

A second lunar occultation of Uranus occurs on September 29. It is only visible from the south of South Africa, the ocean areas to the south and parts of Antarctica.

Neptune is at opposition on the 1st. It then rises 15 minutes before sunset and sets a few minutes after sunrise. By the end of the month Neptune sets an hour before sunrise. The planet remains in Aquarius at magnitude 7.8, so is quite easily seen in binoculars. The near full moon is closest to Neptune on September 26.

Pluto continues to be in Sagittarius all September with a magnitude 14.3 to 14.4.

Brighter asteroids:

(1) Ceres is in Sagittarius during September fading a little from magnitude 8.2 to 8.7 during the month. The dwarf planet will be slow moving in Sagittarius, being stationary on the 15th. It will then be about 3.5° from the M55 globular cluster.

(4) Vesta is in Cetus throughout September brightening from magnitude 6.7 to 6.3 during the month. The asteroid rises at 8.16 pm on the 1st. By the end of September it will rise about 40 minutes before sunset and set nearly an hour after sunrise.

(9) Metis is in Aquarius, starting the month at magnitude 9.2. It will then rise at the time of sunset but not set until well after sunrise. The asteroid is at opposition on September 6. By the end of the month it will have dimmed slightly to magnitude 9.6

(15) Eunomia starts September in Andromeda with a magnitude 8.4. It moves into Pegasus on the 22nd. Opposition is at the end of September when Eunomia will have brightened to 7.9. It will then be the second brightest asteroid in the sky. , having crossed into Pegasus on the 22nd.

(29) Amphitrite starts September at magnitude 9.9. It is in Aries and stationary on the 7th. By the 30th it will have brightened to magnitude 9.3 and be just under 5° from the star beta Ari.

Brian Loader  
New Zealand