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What’s In September’s Night Skies

Both Mercury will reappear and join Venus in the early September evening sky around 6 to 7 pm from the middle of September in the Virgo (The Virgin) Constellation. Venus will reappear earlier at the end of the first week of September in the Leo (The Lion) Constellation before joining Mercury in the Virgo (The Virgin) Constellation.

Jupiter, the king of the planets can be still be found in the Ophiuchus (The Serpent-bearer) Constellation this month. It’ll be viewable at the start of the night throughout the month, at the beginning of September, Jupiter will set at 01:35 am (AWST) and by the end of the month it’ll at 11:51 pm (AWST). Saturn is still below Jupiter in the Constellation of Sagittarius (The Centaur with a Bow) and it’ll be viewable at the start of the night throughout the month. At the beginning of September, Saturn will set at 03:41 am (AWST) and by the end of the month it’ll at 01:46 am (AWST). On the 8th of September, we’ll see from Perth, the Moon occult (pass over) Saturn from 10:00 pm (AWST) to 11:03 pm (AWST).

Mercury and Venus on the 15/09/19 at 07:00 pm. Image Credit: Stellarium Jupiter and Saturn on the 15/09/19 at 08:00 pm. Image Credit: Stellarium The Moon moving away from Saturn after occulting the planet on the 08/09/19 at 11:03 pm. Image Credit: Stellarium

Uranus can be found in the Constellation of Cetus (The Sea Monster) in the early evening this month. It’ll rise at 10:21 am (AWST) at the start of September and by the end of the month it’ll rise at 07:43 pm (AWST). Neptune, the last planet in our Solar System can be found in the early morning sky in between the Constellations of Aquarius (The Water Bearer), Cetus (The Sea Monster) and Pisces (The Fish) the whole of September. The planet will rise at 06:32 pm (AWST) at the beginning of September and will be viewable at the start of the night at the end of the month.

Uranus on the 15/09/19 at 01:00 am. Image Credit: Stellarium Neptune on the 15/09/19 at 10:00 pm. Image Credit: Stellarium

Conjunctions and Occultation

Conjunctions involve object(s) in the Solar System and/or more distant objects, such as a star. It’s an apparent phenomenon in which multiple objects which aren’t close together appear close in the sky and it’s caused by the observer’s perspective. An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer.

  • 02/09/19 – Conjunction of the Moon and Spica (Where to look)
  • 05/09/19 – Conjunction of the Moon, Antares and Jupiter (Where to look)
  • 06/09/19 – Conjunction of the Moon, Antares, Jupiter and Saturn (Where to look)
  • 07/09/19 – Conjunction of the Moon, Antares, Jupiter and Saturn (Where to look)
  • 08/09/19 – Conjunction of the Moon and Saturn (Where to look)
  • 21/09/19 – Conjunction of the Moon and Aldebaran (Where to look)
  • 24/09/19 – Conjunction of the Moon, Castor and Pollux (Where to look)
  • 30/09/19 – Conjunction of the Moon, Spica, Mercury and Venus (Where to look)

Astronomical Events This Month:

Zodiacal Light Season Begins

The Zodiacal Light. Image Credit & Copyright: Alan DyerThe Zodiacal light season begins on the 1st of September. As the Sun approaches the September Equinox on the 22nd of September causes the back-scattering of light off of dust particles spread out along the ecliptic plane (The apparent path of the Sun’s motion on the celestial sphere as seen from Earth). Spring and Autumn are the best times to see this pearly glow in the dawn or dusk. This is due to the steep angle of the ecliptic relative to our horizon. The September Equinox season favours dusk for the Southern Hemisphere, and dawn for the Northern Hemisphere; and the reverse is true near the March equinox.

To see the zodiacal light, go out around an hour after sunset or an hour before dawn, and look from as darker a site as possible. Any light pollution or faint glow from distant cities on the horizon will destroy the ethereal glow. The zodiacal light will appear as a slender pyramid-shaped glow, tracing the length of the ecliptic plane.

The September Equinox

Equinoxes and Solstices. Image Copyright: timeanddate.comOn Monday the 23nd of September, The Southward Equinox occurs at 03:50 pm (AWST), marking the beginning of astronomical Fall for the Northern Hemisphere, and the start of Spring for the Southern Hemisphere. This is an exact moment when the Sun’s declination equals 0 as seen from the Earth. The two points where the ecliptic or the imaginary path the Sun seem to trace out along the celestial sphere meets the celestial equator are known as the equinoctial points.

In the 21st century, the September Equinox last fell on September 22nd on 2016 and will fall on the 22nd or the 23rd until 2092, when it will begin falling on September 21st every fourth year.

The Equinox (literally meaning ‘equal nights’ in Latin) means that night and day are nearly equal worldwide, and that the Sun rises due east of an observer on the equinox and sets due west. The Full Moon nearest to the September Equinox is known as the Harvest Moon, a time when farmers use the extra illumination at dusk to bring in crops. In 2019, the Harvest Moon actually falls on September 22nd.

The term Equilux is sometimes used to discern the difference between the true Equinox and the point when sunlight length actually equals the length of the night. Several factors play a role in this, including the time it takes the physical diameter of the Sun to clear the horizon, atmospheric refraction, and the observer’s true position in their respective time zone. The Equilux occurs within a few days of either Equinox.

Things to Look at This Month:


Albireo is a double star that is 390 light years away from us located in the constellation Cygnus. Albireo is the “beak star” in Cygnus the Swan. The origin of the name is through several mistranslations between Greek, Arabic and Latin. It is a good wide double star with strong colour contrast, possibly the best available to modest telescopes. It is low in the North and only available for a few months of the year during the late winter and spring. The primary star is yellow/amber in colour whilst its companion is blue/green.

The primary star is, in fact, a close binary also, however, it is too close and faint to detect without very large telescopes and excellent observing conditions. The stars revolve around one another in about ~100 000 years. The primary star is ~5 times the mass and ~1 200 times brighter than the sun but with a cooler surface temperature of ~4 100 K. The secondary star is ~3.2 times the mass and ~230 times the brightness of the sun with a surface temperature of ~12 000 K.

Albireo on the 15/09/19 at 9:00 pm. Image Credit: Stellarium Albireo. Image Credit: Palomar Observatory/STScI/WikiSky

Ptolemy Cluster:

The Ptolemy’s Cluster (M7 & NGC 6475) is a large open cluster near the sting of the tail of the constellation of Scorpius. While it’s 980 light years away from us, it’s large enough to be seen with the unaided eye in a dark sky and is a nice sight in binoculars. The cluster is 25 light-years across and it contains around 100 stars in total. It was first described by the Greek-Roman astronomer Ptolemy in 130 AD from which it gets its common name of Ptolemy’s cluster. The colour of the stars in this cluster is predominately yellow, indicating this is an older cluster, with an estimated age of 260 million years. Clusters which contain many hot blue stars, like the Pleiades, are considerably younger.

Ptolemy Cluster on the 15/09/19 at 09:00 pm. Image Credit: Stellarium Ptolemy Cluster. Image Credit & Copyright: Lorand Fenyes

Trifid and Lagoon Nebulas:

The Trifid Nebula (M20 & NGC 6514) and Lagoon Nebula (M8 & NGC 6523) can be found close to in the constellation of Sagittarius.

The Trifid Nebula is an emission (pink) and reflection (blue) nebula, with open star cluster, found in Sagittarius. The Trifid (Meaning “divided into three lobes”) comes from the three-pronged dark lanes (dark nebulae) through the nebula that blocks off the light behind. The nebula is 2,660 light-years away and is 15 light-years across.

The central star formation “nursery” where hot young stars power the emission nebulae. Infrared telescopes have shown there 30 embryonic and 120 newborn stars not yet bright enough to emit light in the visible light part of the light spectrum. The new stars are very young at 400,000 years old with the central star in the nebula actually a cluster of four star systems, two of which are close binaries, making six stars in all.

The Lagoon Nebula is, sometimes called the “Hourglass Nebula” (not to be confused with the true “Hourglass Nebula” in the constellation of Musca), is a very young nebula, perhaps less than 10,000 years. The nebula is further away than the Trifid Nebula at 4,100 light-years away and it’s a lot bigger with the nebula being 100 light-years across and 50 light-years high. It is one of the finest and brightest star-forming regions in the sky and contains many “Bok globules”, which contain dense cosmic dust and gas from which star formation may take place. The central emission area is energised by a bright ultraviolet “O4” class star and it’s a relatively easy object for amateur astrophotographers.

Trifid and Lagoon Nebulas on the 15/09/19 at 09:00 pm. Image Credit: Stellarium Trifid Nebula and Lagoon Nebula. Image Credit: Paulo Cacella

The Sculptor Galaxy:

The Sculptor or the Silver Coin Galaxy (NGC253) is a barred galaxy in the Sculptor constellation roughly 67,000 light years in width. It was discovered by Caroline Herschel in 1783, whilst carrying out a comet search. It is one of the Sculptor group of galaxies, which is grouped around the south galactic pole (These galaxies are sometimes named “The South Polar Group”). The Sculptor group may be the next closest group of galaxies beyond our Local Group, located about 11.5 million light-years from Earth.

Often called a Starburst galaxy because it has a large number of stellar nurseries in which many hot young blue stars are being formed. This is due as a result of a collision with a dwarf galaxy approximately 200 million years ago. The process of star formation and subsequent explosion as supernovae occurs at an unusually high rate of star birth.

These young stars emit radiation that causes the hydrogen gas to glow brightly in pink. NGC253 has many Wolf Rayet stars (WR stars start off as hot massive stars, around x20 solar masses, that rapidly lose mass by blowing their hydrogen envelope away in the form of high-velocity stellar winds.) The Silver Coin Galaxy also has a large proportion of dust, although not in clearly defined lanes, such as those found in the Milky Way Galaxy.

With an apparent magnitude of 7.2, it’s the second easiest galaxy to see after Andromeda and not including the Milky Way’s two satellite galaxies (The Large and Small Magellanic Clouds). With good viewing conditions, it can be seen with binoculars with a long axis ~2/3 of the full moon.

Sculptor Galaxy on the 15/09/19 at 09:00 pm. Image Credit: Stellarium Sculptor Galaxy - Image Credit & Copyright: Mike O'Day

47 Tucanae:

47 Tucanae (NGC 104) is the second largest and second brightest globular cluster in Milky Way. The Globular cluster is 16,000 light years away from us and is located in Constellation Tucana (Named after the Tucan bird) and it’s a naked eye “star” and clearly visible in binoculars as a “fuzzy blob”. Omega Centauri contains at least 1 – 2 million stars and the cluster has a diameter of roughly 120 light-years and the stars are roughly 10 billion years old. The average distance between the stars at the centre is around 10% of a light year or more than 100 times the diameter of our solar system. In February 2018, indirect evidence for a likely intermediate-mass black hole in 47 Tucanae was announced.

47 Tucanae on the 15/09/19 at 9:00 pm. Image Credit: Stellarium 47 Tucanae. Image Credit & Copyright: Mike O'Day

Phases of The Moon:

September 2019 Moon phases

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