OBSERVING GUIDE (Please note all times are ST and are based on an observing location of Belfast and covers the month of May)
At the start of the month, the Sun rises at 05:45 and set at 20:55. By month's end, it rises at 04:55 and sets at 21:45.
Mercury is at greatest western elongation on the 17th, but it is not readily visible this month.
Venus is a morning object in May. It rises at 04:40 at the start of the month, by month’s end it rises at 03:40. It fades from mag -4.4 to mag -4.2 during the month.
Mars is visible in the evening sky this month in Taurus. It is visible as soon as darkness falls during the month and sets at 23:10 by month’s end. It fades from mag +1.8 to mag +1.9 during the month.
Jupiter is visible in the evening sky this month in Virgo. During the month, it is visible as soon as darkness falls and sets at 03:15 by month’s end. It fades from mag -2.2 to mag -2.1during the month.
Saturn is visible this month in Sagittarius. By month’s end, it becomes a late evening object. At the start of the month, it rises at 00:55, by month’s end it rises at 22:45. It brightens from mag +1.1 to mag +1.0 during the month.
Uranus is not readily visible this month.
Neptune is visible in the morning sky in Aquarius by month’s end. It rises at 02:30 and is mag +7.9.
The first quarter moon is on the 3rd (03:47) with the full moon on the 10th (22:42).
The last quarter moon is on the 19th (01:33) with the new moon on the 25th (20:44).
3rd pm the waxing gibbous lies SW of Regulus (Alpha (α) Leonis, mag +1.4) at 22:00.
4th pm the waxing gibbous lies NE of Regulus (Alpha (α) Leonis, mag +1.4) at 22:00.
7th pm the waxing gibbous lies N of Jupiter at 22:00. 8th pm the waxing gibbous lies NE of Spica (Alpha (α) Virginis, mag +1.0) and E of Jupiter at 22:00.
11th pm the waning gibbous lies N of Antares (Alpha (α) Scorpii, mag +1.0) at midnight. 12th pm the waning gibbous lies NE of Antares (Alpha (α) Scorpii, mag +1.0) at midnight.
14th am the waning gibbous lies NE of Saturn at 01:00.
20th am the waning crescent lies W of Neptune at 04:00. 22nd am the waning crescent lies W of Venus at 05:00.
23rd am the waning crescent lies SE of Venus at 05:00.
27th pm the waxing crescent lies E of Mars at 22:00.
31st pm the waxing crescent lies NE of Regulus (Alpha (α) Leonis, mag +1.4) 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.
The Eta Aquarids peak on the morning of the 6th with a theoretical ZHR of 50. However the radiant only rises in the morning twilight shortly before sunrise on the morning of the 6th from Ireland. This leads to a very short observing window with a much reduced ZHR given the very low radiant. The waxing gibbous moon sets on the morning of the 6th at 04:30 in Leo.
There may be additional minor showers this month, details of which can be found in the below Information Sources and Links Section.
There are no bright asteroids at opposition this month. Finder charts and further information about other fainter asteroids can be found in the below Information Sources and Links Section.
Comet C/2015 V2 (Johnson) is currently mag +9 and brightening slowly. In April, it will be in Bootes and will be circumpolar. It is predicted to peak at mag +6 during the summer. It lies near Alkalurops (Mu (μ) Bootis, mag +4.3) on the night of the 13th/14th. Between the 19th and 21st, it lies near Princeps (Delta (δ) Boots, mag +3.5). On the night of the 27th/28th, it lies near to Izar (Epsilon (ε) Bootis, mag +2.4).
Comet C/2015 ER61 (PanSTARRS) is currently mag +6 and is predicted to reach peak brightness in May. This month, it will be a morning object in Pisces. It will be visible around 04:00 during the month in the dawn sky. It can be located in the circlet asterism between the 7th and the 11th. It enters it close to Kappa (κ) Piscium, mag +5.0 and leaves to the N of Lambda (λ) Piscium, mag +4.5. Comet 41P/Tuttle-Giacobini-Kresak is currently mag +6 and has peaked in brightness. It is now expected to fade in May. It is circumpolar and is in Hercules during the entire month. 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 Leo, we have several galaxies on view including The Leo Triplet - M65, M66 and NGC 3628. M95, M96 and M105 can also be observed in Leo. The place to really find galaxies is in Virgo. The Virgo Super Cluster can be found here with numerous galaxies on view. Also in Virgo, M104 - the Sombrero Galaxy can be found. In Coma Berenices, there is M64 - the Black-Eye Galaxy. Also check out the constellation Canes Venatici with the globular cluster - M3 and several galaxies including M51 - the Whirlpool Galaxy and M63 - the Sunflower Galaxy. In Hercules, two globular clusters - M92 and the excellent M13 can be observed and in Lyra - M57 - The Ring Nebula can be observed. Finally there are some excellent open clusters in Cancer - M44 - The Beehive Cluster and M67.
Always keep an eye out for Aurorae. The night sky does not get fully dark this month. Between mid-May and the early August, Astronomical twilight is present at night. This is when the sun is between twelve and eighteen degrees below the horizon. This time of year is very good for observing the numerous satellites and other objects in orbit above us. Watch out for NLCs - Noctilucent Clouds during May. Look to the North-West for a white/silvery glow 1.5 - 2 hours after sunset and to the North-East a similar amount of time before sunrise. They can sometimes be faint, sometimes bright.
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.