The September night sky
So what do we have to look at above us as we moved from summer and into autumn. The nights become longer, which mean longer nights for observing, but that is often curtailed as we move towards unsettled weather.
The host of watery constellations in this month’s celestial tableau matches the theme of unsettled weather. The constellation we look at in this issue is Aquarius (the water carrier). You can also observe Cetus (the sea monster), Capricornus (the sea goat), Pisces (the fishes), Piscus Austrinus (the southern fish) and Delphinus (the dolphin).
Jupiter dominates the evening sky. Which will be brilliant after sunset and Venus, as the morning star heralding the dawn.
Constellations through which the ecliptic passes this month are Libra (the Scales), Sagittarius (the Archer), Capricornus (the Goat), Aquarius (the Water Carrier), Piscis (the Fishes), Aries (the Ram) and Taurus (the Bull) is about to rise over the eastern horizon.
The constellation of Libra (the Scales) moves below the western horizon early in the evening. Just over the south western horizon is the constellation of Sagittarius (the Archer). It is really a southern constellation but we can see the upper part creep along the horizon during the summer.
The central bulge of our galaxy is located in Sagittarius so the richest star fields can be found in the constellation along with many of the beautiful and interesting deep sky objects that you may wish to seek out.
The summer constellations are still prominent in the night sky lead by Hercules (the Hunter). Following Hercules is the Summer Triangle with its three corners marked by the bright stars: Deneb in the constellation of Cygnus, Vega in Lyra, and Altair in Aquila. The Summer Triangle is very prominent and can be used as the starting point to find our way around the night sky.
The Milky Way (our Galaxy) flows through the Summer Triangle passing through Cygnus, down to the horizon in Sagittarius. The Milky Way flows north from the Summer Triangle through the rather indistinct constellation of Lacerta (the Lizard), past the pentagon shape of Cepheus and on through the ‘W’ shape of Cassiopeia (a Queen).
Mercury is too close to the Sun in the evening sky to be observed during the whole of September.
Venus is the brightest ‘stellar’ object in the morning sky, rising between 1 ans 2am September. The planet’s visual magnitude is -4.2, and through a telescope exhibits a gibbous phase. It lies at a distance of just less than 1 astronomical unit (the mean Sun-Earth distance). The waning crescent Moon with earthshine is in conjunction with Venus during the morning of the 14th, when the two are almost 4°apart. This takes place in the constellation of Cancer the Crab, with the beautiful Praesepe cluster, M44, between the two. The star just to the north of the Moon is Ascellus Borealis (Northern Ass), and the star just 1° to the upper left of Venus is Ascellus Australis (the Southern Ass)
Mars grows brighter as the month progresses as it heads towards its opposition on October 13th. The planet’s visual magnitude increases from -2.0 to -2.5. The ‘Red Planet’ is a conspicuous object in the September night sky, rising soon after sunset in the western part of the constellation of Pisces, where it stays till after opposition. The planet has an angular diameter of around 21 secs of arc during September. During the morning of the 6th, there is a beautiful close conjunction between the waning gibbous Moon and Mars. The planet lies less than a degree to the north of the Moon, and this will give astrophotographers to capture the two on a single image. The sight of the two together in the sky will be spectacular to the unaided eye and in binoculars
During September, Jupiter is an evening object, setting at midnight as the month begins and at 10pm at the end of the month. It lies in the constellation of Sagittarius and so never attains a great altitude as seen from the UK. Saturn lies some 8° to the east of Jupiter and of theoretical interest, the planet lies between these two major planets. Jupiter’s visual magnitude is -2.4 during the month. The Moon, just after first quarter may be seen approaching Jupiter on the evening of the 24th; on that evening Jupiter lies 6° to the upper left of the Moon. Take the opportunity to observe the Galilean satellites; Io, Europa, Ganymede and Callisto as the configuration changes on a nightly basis. Identification of the satellites is to be found on the Front Page of the Sky Notes.
As mentioned above, both Jupiter and Saturn, are in the constellation of Sagittarius; however Saturn is much fainter than Jupiter, with a visual magnitude of +0.4. Saturn and the Moon are in conjunction in the evening of the 25th, when at 9pm Saturn is 3.5° north of the waxing gibbous Moon.
Uranus at magnitude +5.69 lies in Aries is visible most of the night. Through an astronomical telescope has the appearance of a tiny greyish green disc. Uranus lies just over 10° to the south of Hamal, the constellation’s brightest star
Neptune comes into opposition and its nearest to the earth on the evening of the 11th. It lies in the constellation of Aquarius, just south of the Pisces border. The planet’s magnitude is +7.83, too faint to be seen by the unaided eye, but visible in binoculars less than a moon-width to the lower left of the +5.5 magnitude star 96 Aquarii as a bluish point of light
This month on Tuesday, 22nd September we have the autumn equinox.
At this moment 2.30pm; the instant of the September equinox, the midday sun will be at zenith, or straight overhead, at the Earth’s equator. That’s the meaning of equinox. The September equinox sun crosses the sky’s equator, going from north to south. Because the path of the sun is heading southward, this equinox signals the beginning of autumn in the Northern Hemisphere and spring in the Southern Hemisphere.
On the day of the equinox, the sun rises due east and sets due west all over the world, with everyone worldwide receiving Approximately equal portions of day and night.
This is the best time of year to see the zodiacal light, also known as the false dawn. This is your chance to catch the zodiacal light before dawn’s first light.
You need a dark sky location to see the zodiacal light, someplace where urban
lights aren’t obscuring the natural lights in the sky. The zodiacal light is a pyramid-shaped glow in the east before dawn (or after twilight ends in the evening.
It’s most visible before dawn at this time of year because, as seen from the Northern Hemisphere, the ecliptic – or path of the sun, moon and planets – stands nearly straight up with respect to the eastern horizon before dawn now.
The Aurora season has started early and there may be opportunities to see the northern lights this month. There are regular updates on https://www.facebook.com/aurorawatchuk/
The Moon phases:-
Full Moon 2nd September
Last quarter 10th September
New Moon 17th September
First quarter 24th September