Monthly guide to 'The sky at night'. September 2015.
On 28 September there will be a total eclipse of the Moon which will be visible over the United States, South America, Europe, and Africa. Sadly on this occasion observers in Australia and Philippines will miss out.
The Moon will be at Perigee, closest to the earth on this date making it a Super Moon, and it will be in the zodiacal constellation of Pisces (the fishes) directly below the square of Pegasus.
A lunar eclipse occurs when the Moon passes through the earth’s shadow cast in space. The eclipse begins at 01:07 UT as the Moon passes into the Earth’s lighter penumbra shadow, and the maximum lunar eclipse will take place between 02:11 UT to 03:23 UT as the Moon moves through the earth’s darker umbra shadow, and the Moon will then be seen orange, or red in colour making a splendid photo opportunity.
The Autumn equinox occurs on 23 September which is when the Sun passes across the celestial equator from north to south, and night and day are of equal length. At the latitude
of Australia the sunsets at 17:38 UT at the beginning of the month. At the end of September the Sun sets 18 minutes earlier at 18:00 UT. At the latitude of the UK the sunsets at 18:43 UT and 55 minutes earlier at the end of the month.
The nights are clearly beginning to get longer and there are some interesting photo opportunities for amateur astronomers to look forward to during the month. Whether you are a novice or skilled amateur, there is something for everyone.
The bright planets Venus, Mars and Jupiter are now coming into view in the eastern sky before sunrise, and are putting on a splendid show. If you are willing to get up 1½ hours before sunrise to set up your equipment, you should be able to get a nice panorama of the
bright stars of the constellation Leo (the lion) and planets either side of Regulus (Alpha Leonis) the brightest star.
As for the planets themselves.
Mercury is visible rather low in the western sky after sunset, reaching greatest eastern elongation on 4 September. The planet shines at Mag +0.1 at the beginning of the month and fades to +2.8 at the end as the planet’s phase increases from half or dichotomy to New during the month. Mercury is at Superior conjunction on 30 September.
The planet is a disappointment for planetary observers unless you have a moderate telescope, as the angular diameter of Mercury is so small. It is 6.8 arc seconds on 1 September, and 10.3 at the end of the month, by which time you should be able to glimpse
the planet’s splendour crescent phase.
Venus passed through Inferior conjunction on 15 August when its phase was New, and has now reappeared in the eastern sky before sunrise shining at Mag -4.6. The planet lies on the border with Cancer, with the head of Hydra (the water serpent) below, and cannot be mistaken because of its brilliance. It reaches its stationary point on 5 September.
The planet lies in the constellation of Cancer below the Mag +4.6 star Acubens at the beginning of the month, before moving into Leo. Venus will be 10˚ S of the Moon on 10 September, and will be at its greatest brightness, Mag -4.8 on 15 September, so that it make
a nice photo opportunity.
The phase of Venus can be seen in small telescopes. It grows from a slender crescent towards 35% illumination during the during September, although dichotomy (half) is not expected until 25 October. The angular diameter of Venus decreases from 50 arc seconds at the beginning of the month, to 35 at the month’s end.
As September opens Mars lies in the constellation of Cancer, and is moving retrograde into Leo. The planet will be 5˚ N of the crescent Moon on 10 September, and 0.8˚ N of the bright star Regulus on 24 September making two fine photo opportunities.
Mars did not come to opposition during 2015, and due to its great distance from us it remained a telescopic disappointment. The planet was in conjunction with the Sun on 14 June, and the new apparition of Mars has now begun for planetary observers, as Mars comes into view above the eastern horizon before sunrise.
The planet’s angular size is small at the moment, around 3.8 arc seconds, due to the planet’s distance of 368 million Km. However, as the earth moves around the Sun Mars is getting closer to us all the time, so that at opposition in May 2016 the planet will be 141million Km closer to us. The planet’s angular size will then be just under 18 arc seconds.
The bright Asteroid Vesta will be at opposition on 16 September. Shining at Mag +6.4 it lies in the constellation of Cetus (the whale) NW of the Mag +3.4 star Dheneb, and close to the star 25 Ceti. Vesta is visible in 10 x 50 binoculars, although you will need to make a drawing of the star field on two separate occasions.
Sept 08 RA 00h 56m 26.8s DEC -06˚ 21′ 59″ Mag +6.5
Sept 18 RA 00h 49m 5.05s DEC -07˚ 35′ 24″ Mag +6.3
Sept 28 RA 00h 40m 13.8s DEC -08˚ 44′ 05″ Mag +6.3
Vesta will then have moved against the more distant stars revealing itself; you will know that you have found the asteroid.
Vesta was discovered by the German astronomer Heinrich Wilhelm Olbers on 29 March 1807, and is a potato shaped asteroid about 570 x 460 km in size. It lies within the main asteroid belt between the planets Mars and Jupiter, and was visited by the DAWN spacecraft in 2011, which sent back some amazing photographs and science.
Shining at Mag -1.7 Jupiter lies in the constellation of Leo below the lion’s body west of Regulus. This giant planet is now making its appearance in the morning sky as it moves further away from the sun. Its elongation will be 33˚ at the end of the month.
Jupiter’s angular diameter is about 31 arc seconds so the cloud belts can be seen even with small telescopes, along with the four Galilean moons: Io, Europa, Ganymede and Callisto, as they change position around Jupiter during the month. A telescope of 6 inch (150cm) is the
minimum size to make useful observations.
The ringed planet Saturn is visible low in the western sky after sunset shining at Mag -1.7, and lies in the constellation of Libra (the scales). The planet will be 3˚ S of the near half Moon on 19 September making a nice photo opportunity.
While the splendid ring system is fully on view, the equatorial diameter is only about 16 arc seconds, which is half that of Jupiter. While you will be able to see the rings with small telescopes, an aperture of 8 in (200 cm) will be required to do useful work.
The Night Sky.
In the northern hemisphere the southern sky is dominant. During September evenings the Summer Triangle is high up in the night sky, composed of the three bright stars Deneb in Cygnus (the swan), Altair in Aquila (the eagle), and Vega in Lyra (the lyre or harp).
In this month’s Astronomy & Space program we take a look at ‘The Swan in the Sky’ followed from 15 September by a chance to watch again: ‘The Autumn Sky’.
In the southern hemisphere the northern sky is dominant and the winter constellations are on view high up, including Canis Major (the greater dog), Orion (the hunter), Taurus (the bull), and Gemini (the twins).
alongside other prominent constellations of the far south, including Puppis (the stern), Vela (the sails), Horogium (the pendulum clock) and Hydrus (the lesser water snake).
The Autum comet C/2013 US10 Catalina.
This bright comet makes a nice photo opportunity for southern hemisphere observers.
Sept 4/5 RA 15h 16m DEC -56˚ 50′
Sept 14/15 RA 14h 52.8m DEC -48˚ 31′
Sept 24/25 RA 14h 41.7m DEC -41˚ 37′
Catalina continues to put on a nice display for southern hemisphere observers, and is easily visible in a pair of 10×50 binoculars During September. It is can be seen moving along its celestial path
through the constellation Triangulum Australe (the southern triangle) into Lupus (the hare).
Catalina continues to get brighter from Mag +7 to +6.8 during the month, while its splendid tail is prominent. The comet’s Ephemeris here is taken from the BAA Handbook.
There is much to see this month, and the splendour of the total eclipse of the Super Moon to look forward to That’s all for now, I will be back in October to give another update — keep looking up!