(Please note all times are ST and are based on an observing location of Belfast and covers the month of September)
At the start of the month, the Sun rises at 06:30 and sets at 20:15. By month's end, it rises at 07:25 and sets at 19:00.
1st and 2nd am Venus and M44
5th am Mars and Regulus (Alpha (α) Leonis, mag +1.4)
10th am Mercury and Regulus (Alpha (α) Leonis, mag +1.4)
16th and 17th am Mercury and Mars
20th am Venus and Regulus (Alpha (α) Leonis, mag +1.4)
Mercury is at greatest western elongation on the 12th and is visible mid-month before sunrise. On the morning of the 12th, it rises at 05:10 and is mag -0.2.
Venus is a morning object in September. It rises at 03:30 at the start of the month, by month’s end it rises at 05:00. It maintains it brightness at mag -3.8 during the month.
Mars is a morning object this month. It rises at around 05:20 and maintains its brightness at mag -1.8 during the month.
Jupiter is not visible this month.
Saturn is at eastern quadrature on the 14th and is visible this month in Ophiuchus. During the month, it is visible as soon as darkness falls and sets at 21:50 by month’s end. It fades from mag +0.4 to mag +0.5 during the month.
Uranus is visible in the evening sky this month in Pisces. At the start of the month, it rises at 21:25, by month’s end it rises at 19:30. It maintains its brightness at mag +5.7 and lies near to Torcularis Septentrionalis (Omicron (ο) Piscium, mag +4.3) during the month.
Neptune is at opposition on the 5th and is visible in the evening sky this month in Aquarius. At the start of the month, it rises at 20:20 and by month’s end it rises during daylight hours. It maintains its brightness at mag +7.8 and lies near to Lambda (λ) Aquarii, mag +3.7 during the month.
The full moon is on the 6th (08:03). The last quarter moon is on the 13th (07:25) with the new moon on the 20th (06:30). The first quarter moon is on the 28th (03:54).
5th pm the waxing gibbous lies W of Neptune at 22:00.
9th pm the waning gibbous lies SE of Uranus at 22:00.
12th am the waning gibbous lies NW of Aldebaran (Alpha (α) Tauri, mag +0.9) and S of M45 – The Pleiades at 00:00.
13th am the waning gibbous lies SE of Aldebaran (Alpha (α) Tauri, mag +0.9) at 00:00.
18th am the waning crescent lies SE of Venus and Regulus (Alpha (α) Leonis, mag +1.4) and NW of Mercury and Mars at 06:00.
19th am the waning crescent lies SE of Mercury and Mars at 06:00.
21st pm the waxing crescent lies W of Jupiter at 20:00.
22nd pm the waxing crescent lies NE of Jupiter at 20:00.
25th pm the waxing crescent lies NW of Antares (Alpha (α) Scorpii, mag +1.0) at 20:00.
26th pm the waxing crescent lies NW of Saturn at 21:00.
The best time to observe meteor showers is when the moon is below the horizon; otherwise its bright glare limits the number you will see especially the fainter ones. Below is a guide to this month's showers.
There are no bright meteor showers this month.
There may be additional minor showers this month, details of which can be found in the below Information Sources and Links Section.
Asteroid (89) Julia is at opposition on the evening of the 6th in Pegasus. It is mag +9.0 and visible from 20:00 on the evening of the 6th.
Finder charts and further information about other fainter asteroids can be found in the below Information Sources and Links Section.
Comet C/2017 O1 (ASAS-SN) peaks around mag +7 in October and is currently mag +10. It will start the month in Taurus, before moving into Perseus by month’s end. It passes to the W of Lambda (λ) Tauri, mag +3.4 around the 7th. It then passes to the E of M45 around the 17th and to the E of Menkhib (Zeta (ζ) Persei, mag +2.8) around the 25th.
Finder charts and further information about the above and other fainter comets can be found in the below Information Sources and Links Section. Any of the above estimates are based on current information at the time of writing the guide and can be wrong - “Comets are like cats; they have tails, and they do precisely what they want”, David H Levy.
On the deep sky front this month, galaxies M81 and M82 can be observed in Ursa Major. In Hercules, two globular clusters - M92 and the excellent M13 can be observed and in Lyra - M57 - The Ring Nebula can be observed. In Vulpecula - M27 - The Dumbbell Nebula can be found. In Andromeda, M31 - The Andromeda galaxy can be observed along with its satellite galaxies M32 and M110. In Perseus, there is the open cluster M34 and the excellent Double Cluster - NGC 869 and 884. In Triangulum, there is the galaxy M33. Finally Auriga is reappearing with its three open clusters M36, M37 and M38 as is Taurus with the excellent Pleiades - M45 and the Hyades.
Always keep an eye out for Aurorae. The autumn equinox is on the 22nd which sees the end of summer and the beginning of autumn. This is the day where the length of day and night is the same and after this the night will take over cumulating with the shortest day of the year on the winter solstice in December. Other interesting naked eye phenomena to look out for include the Zodiacal Light and the Gegenschein. Both are caused by sunlight reflecting off dust particles which are present in the solar system.
The Zodiacal Light can be seen in the West after evening twilight has disappeared or in the East before the morning twilight. The best time of year to see the phenomenon is late-Feb to early-April in the evening sky and September/October in the morning sky - it's then that the ecliptic, along which the cone of the zodiacal light lies, is steepest in our skies. The Gegenschein can be seen in the area of the sky opposite the sun. To view either, you must get yourself to a very dark site to cut out the light pollution. When trying to observe either of these phenomena, it is best to do so when the moon is below the horizon. A new appendix has been added explaining some of the more technical terms used in the guide.
The ZHR or Zenithal Hourly Rate is the number of meteors an observer would see in one hour under a clear, dark sky with a limiting apparent magnitude of 6.5 and if the radiant of the shower were in the zenith. The rate that can effectively be seen is nearly always lower and decreases as the radiant is closer to the horizon. The Zenith is the overhead point in the sky.