(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 pm Venus and Spica (Alpha (α) Virginis, mag +1.0)
6th am Mercury and Regulus (Alpha (α) Leonis, mag +1.4)
Mercury is at superior conjunction on the 21st and is visible in the morning sky for the 1st half of the month. At the start of the month, it rises at 04:55 and is mag -0.8 in Leo.
Venus is visible in the evening sky at the start of the month, but is not visible by month’s end. At the start of the month, it sets at 20:50 and is mag -4.3 in Virgo.
Mars is visible in the evening sky during the month. At the start of the month, it sets at 01:55. At month’s end, it sets at 00:55 and fades from mag -2.1 to mag -1.3 during the month. It is in Capricornus during the month.
Jupiter is an evening object this month in Libra. It sets at 22:00 at the start of the month and by month’s end, it sets at 20:15. It fades from mag -1.8 to mag -1.7 during the month.
Saturn is at Eastern Quadrature on the 26th and is an evening object in Sagittarius during the month. At the start of the month, it sets at 00:25 and by month’s end, it sets at 22:30. It fades from mag +0.4 to mag +0.5 during the month.
Uranus is an evening object in Aries during the month. At the start of the month, it rises at 21:35. By month’s end it rises at 19:40. It maintains its brightness at mag +5.7 during the month.
Neptune is at opposition on the 7th and is an evening object in Aquarius. At the start of the month, it rises at 20:25. By month’s end, it rises during daylight hours. It maintains its brightness at mag +7.8 during the month. It lies between Phi (φ) Aquarii, mag +4.2 and Lambda (λ) Aquarii, mag +3.7.
The last quarter moon is on the 3rd (03:37). The new moon is on the 9th (19:01) with the first quarter moon on the 17th (00:15). The full moon is on the 25th (03:52).
2nd am the 63% waning gibbous lies NW of Aldebaran (Alpha (α) Tauri, mag +0.9) and SW of M45 at 00:00.
3rd am the 52% waning gibbous lies NW of Aldebaran (Alpha (α) Tauri, mag +0.9) at 00:00.
8th am the 4% waning crescent lies NW of Mercury at 06:00.
12th pm the 12% waxing crescent lies NW of Venus at 20:00.
13th pm the 20% waxing crescent lies NW of Jupiter at 20:00.
14th pm the 29% waxing crescent lies NE of Jupiter at 20:00.
15th pm the 39% waxing crescent lies NW of Antares (Alpha (α) Scorpii, mag +1.0) at 20:00.
17th pm the 58% waxing gibbous lies N of Saturn at 20:00.
19th pm the 76% waxing gibbous lies NW of Mars at 20:00.
20th pm the 83% waxing gibbous lies NE of Mars at 20:00.
23rd pm the 98% waxing gibbous lies S of Neptune at 20:00.
26th pm the 97% waning gibbous lies SW of Uranus at 21:00.
29th pm the 77% waning gibbous lies NW of Aldebaran (Alpha (α) Tauri, mag +0.9) and N of M45 at 22:00.
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 115 Thyra is at opposition on the 2nd at mag +9.9. It can be found near the Pegasus/Aquarius boundary and is visible from 21:00 on the evenings of the 1st and 2nd.
Asteroid 27 Euterpe is at opposition in the evening of the 5th at mag +9.8. It is also in Aquarius and is visible from 21:00 on the evening of the 5th.
Finder charts and further information about other fainter asteroids can be found in the below Information Sources and Links Section.
Comet 21P/Giacobini-Zinner is predicted to peak at mag +7 in September with it at perihelion on the 10th. It is currently mag +8 and starts the month in Auriga, before moving into Gemini and then into Monoceros by month’s end. At the start of the month it is visible as soon as darkness falls with it getting higher in the sky as the night goes on. By mid-month, it is visible from 02:00 and by month’s end from 04:00. It passes by Capella (Alpha (α) Aurigae, mag +0.1) around the 2nd/3rd and then between the 8th and 11th, passes by M38, M36 and M37. It passes by M35 around the 15th/16th.
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 23rd 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.