Find out what to go out and look at this month
Mercury is visible very low in the Western early evening sky throughout September appearing in the constellation of Virgo (The Virgin). Mercury will reach its greatest elongation in the West on the 14th of September and it’ll begin to make its way back towards the Sun. Venus can also be found in the Western early evening sky and in late September it will move into the constellation of Libra (The Scales) from the constellation of Virgo.
Jupiter and Saturn can be found in the Eastern evening sky. Jupiter can be found in the constellation of Aquarius (The Water-Bearer) while Saturn can be found in the constellation of Capricornus (The Sea-Goat) during September. Jupiter will set at 06:06 am (AWST) and by the end of the month, it’ll set at 04:04 am (AWST). Saturn will set at 5:10 am (AWST) and by the end of the month, it’ll set at 03:12 am (AWST).
Uranus can be found in the evening in the constellation of Aries (The Ram). At the beginning of September, Uranus will rise at 10:59 am (AWST) and by the end of the month, it’ll rise at 09:02 pm (AWST). Neptune will be viewable as well in the evening between the constellation of Aquarius and the constellation of Pisces (The Fish). At the start of September, Neptune will rise at 06:51 pm (AWST) and by the end of the month, it’ll be viewable throughout the night.
Conjunctions And Occultations:
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.
- 03/09/21 – Conjunction of The Moon, Castor and Pollux (Where to look)
- 05/09/21 – Conjunction of Venus and Spica (Where to look)
- 10/09/21 – Conjunction of The Moon, Venus and Spica (Where to look)
- 13/09/21 – Conjunction of The Moon and Antares (Where to look)
- 16/09/21 – Alignment of The Moon, Jupiter and Saturn (Where to look)
- 17/09/21 – Conjunction of The Moon, Jupiter and Saturn (Where to look)
- 18/09/21 – Conjunction of The Moon and Jupiter (Where to look)
- 27/09/21 – Conjunction of The Moon and Aldebaran (Where to look)
Astronomical Events This Month:
Zodiacal Light Season Begins
The 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
On Thursday the 23rd of September, The Southward Equinox occurs at 03:20 am (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 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 2021, the Harvest Moon falls on September 21st.
The term Equilux is sometimes used to discern the difference between the true Equinox and the point when sunlight length 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 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.
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 that contain many hot blue stars, like the Pleiades, are considerably younger.
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 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.
47 Tucanae or 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’. 47 Tucanae 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 2017, indirect evidence for a likely intermediate-mass black hole in 47 Tucanae was announced.