September’s only bright evening planet, Saturn, stands low down in the SW at nightfall where it shines at mag 0.5. It sets 30 minutes before our star map times to leave the sky devoid of bright planets until Mars and Venus appear in the E before dawn, soon to be joined by Jupiter.
The month’s early highlight occurs on Friday night when the last quarter moon approaches Aldebaran in Taurus and occults the star as seen from Britain before dawn on Saturday.
Parts of southern Africa and areas to its S and E witness a partial solar eclipse on the 13th, but much more interesting is the total eclipse of the moon, in fact the harvest moon, on the morning of the 28th. This is also a supermoon since the moon stands at perigee and, indeed, at its closest for 2015. It then appears wider than on average, but only by a barely-noticeable 7% and not the 14% that is sometimes claimed. The latter figure refers to its enlargement over an equally-rare apogee full moon.
The eclipse is visible in its entirety from Britain and, at least partly, from the rest of Europe, Africa and the Americas. The moon encounters the edge of the Earth’s penumbral shadow at 01:12 BST. but the eclipse only becomes obvious as it nears the darker umbra which it reaches at 02:07. Totality lasts from 03:11 until 04:23 when the moon may shine with a dim ochre hue as it crosses the southern part of the umbra in our SW sky. It exits the umbra at 05:28 and the penumbra at 06:23.
Venus, brilliant at mag –4.4 to –4.5 and unmistakable as a morning star, climbs from the ENE to stand almost 15° high in the ESE by sunrise on the 1st and more than twice as high by the 30th. Binoculars show it as a slim crescent as it recedes and shrinks from 51 to 43 arcsec. Catch it close to the waning earthlit moon on the 10th.
Mars, much fainter at mag 1.8, lies 9° above-left of Venus on the 1st, but stands 11° below-left of Venus by the 30th. Jupiter, conspicuous at mag –1.7, emerges from the twilight by mid-month to lie less than 20° below-left of Venus. From the 23rd to the 25th, Mars passes the slightly brighter star Regulus about halfway between Venus and Jupiter in our eastern pre-dawn sky.
September diary
1st 05h Neptune at opposition
4th 11h Mercury furthest E of Sun (27°)
5th 06h Moon occults Aldebaran; 11h Last quarter
10th 07h Moon 2.7° N of Venus
11th 00h Moon 5° S of Mars
13th 08h New moon and partial solar eclipse
19th 04h Moon 2.8° N of Saturn
21st 10h First quarter
23rd 09:21 Autumnal equinox
24th 18h Mars 0.8° N of Regulus
28th 04h Full moon (supermoon) and total lunar eclipse
30th 16h Mercury in inferior conjunction
* Times are BST
