Astronomy Guide May 2023

Dear Stargazer Friends,

I hope you have been well. May is still “Galaxy season”. On that occasion I have added a new chapter to my Astronomy Guide: “The Topic of the Month”. And this month I looked a bit closer at Galaxy Clusters, which I find so fascinating. I hope you will enjoy reading about it. 

Planet Venus continues to shine bright throughout May and will set at 00:43 CEST on 18 May 2023 – 

the latest setting time in 50 years. Jupiter will re-emerge end of May, gradually becoming visible longer in the pre-dawn sky. 

On 5 May, there will be a penumbral lunar eclipse where the Moon will pass through Earth’s shadow. It won’t be visible from most parts of central Europe but people in Asia, Africa, Russia and Oceania will be able to watch this spectacular event. The eta Aquariids will peak on the night of 4-5 May. Unfortunately, the Moon will be full.

Best wishes and clear skies,

Topic of the Month: Galaxy Clusters

Galaxy clusters are some of the largest structures in the universe, made up of hundreds or even thousands of galaxies held together by gravity. Galaxy clusters typically have a spherical or elliptical shape, with the galaxies within them orbiting around a common center. The center of a galaxy cluster is typically dominated by one or more giant elliptical galaxies. Galaxy clusters aren’t randomly distributed in space but seem to be concentrated as clusters in some areas, while other areas of space are almost empty, so-called voids. Galaxy clusters are important for science and can give insights into astrophysical phenomena such as the nature of dark matter and dark energy, the evolution of the universe as well as the formation and growth of galaxies. 

Galaxy Cluster in Virgo
Markarian’s Chain in Virgo Cluster – © Isabel Streit 2022

A fascinating example is the Virgo Cluster, a group of over 2’500 galaxies with a distance to our Milky Way of approximately 70 million light-years. It is at the heart of the larger Virgo Supercluster, of which the so called Local Group containing our Milky Way is a member. The brightest galaxy in the Virgo Cluster is Messier 87, an elliptical galaxy located near the center of the cluster with an apparent magnitude of about 9.6. M87 is known for its supermassive black hole at its center as well as a black-hole-powered jet of electrons and other sub-atomic particles traveling at nearly the speed of light. Visit NASA’s Hubblesite to view an image of the M87 jet.

Another example of a Galaxy cluster is the Coma Cluster located in the constellation of Coma Berenices. At a distance around 350 million light-years away from our Milky Way it appears less bright and smaller than the Virgo Cluster. It is part of the so-called Coma Supercluster, the nearest massive cluster of galaxies to our Virgo Supercluster.

Coma Cluster (Abell 1656) in the Constellation of Coma Berenices – © Isabel Streit 2022 

The Coma Cluster contains more than 1’000 galaxies. Its brightest galaxies have magnitudes ranging from around 10 to 14. The member galaxies of the Coma Cluster are distributed in spherical shape, with a high concentration towards the center of the cluster. The cluster is dominated by elliptical galaxies but also contains spiral and irregular galaxies as well as dwarf galaxies. One of the most striking features of the Coma Cluster is NGC 4874, its dominant central galaxy, which is one of the largest and most massive galaxies in the universe. It’s an elliptical galaxy with billions of stars and a diameter of more than 300’000 light years.

Sources and further reading: 

  • «Kompendium der Astronomie. Einführung in die Wissenschaft vom Universum», Hans-Ulrich Keller, 6. Ausgabe, 2019, Kosmos Verlag, Stuttgart.
  • “Messier 87”, in: Hubble’s Messier Catalog, NASA (visited on 16.4.2023).
  • “Black Hole-Powered Jet of Electrons and Sub-Atomic Particles Streams from Center of Galaxy M87”, in Hubblesite (visited on 16.4.2023).
  • «Webb Telescope Finds Evidence of Massive Galaxies That Defy Theories of the Early Universe», Smithsonian Magazine, 24.2.2023, (visited on 13.4.2023).
  • “Coma Supercluster”, Wikipedia, (visited on 16.4.2023).
  • “Virgo Cluster”, Wikipedia, (visited on 16.4.2023).
  • ChatGPT

Moon phases May

Times for Bern, Switzerland (CET)

Full Moon (Penumbral lunar eclipse, for more information see below)05 May, 19:34
Third Quarter12 May, 16:28
New Moon19 May, 17:53
First Quarter27 May, 17:22 

Meteor Showers May

eta Aquariids
15 April – 27 May 2023
Peak night: 5-6 May 2023 (Full Moon).  The eta Aquariids are best to be observed from the Mediterranean or further south. This is because it’s radiant (Eta Aquarii in the constellation of Aquarius) rises only shortly before dawn in Central Europe. Best observing times are at around 3 a.m.  The Moon will be 100% full, so it’s not an ideal night to observe this meteor shower. Radiant at η Aquarii (Eta Aquarii, constellation of Aquarius). Parent object is Comet 1P/Halley 


American Meteor Society, METEOR SHOWER CALENDAR 2022-2023

Kosmos Himmels-Jahr 2023, Hans-Ulrich Keller, Franck-Kosmos Verlags GmbH & Co. KG, Stuttgart, 2022.


Mercury will be at inferior solar conjunction in the night form 1 to 2 May 2023. The planet will not be visible in May.

Venus keeps shining bright in the evenings. It will continue to gain in magnitude. While it is currently visible in the constellation of Taurus, it will appear in the constellation of Gemini starting 9 May. On 18 May, Venus will set at 00:43 – the latest setting time in 50 years. On 23 May, look out for Venus, the Waxing Crescent Moon and Mars (W, evening).

Mars currently appears in the constellation of Gemini and will move into Cancer on 17 May 2023 (W). It’s magnitude will further decrease as the month progresses (from approx. 1.3 on 1st of May to 1.6 on 30 May).

Jupiter – after the solar conjunction on 11 April 2023, Jupiter will re-emerge end of May, gradually becoming visible for ever-longer periods in the pre-dawn sky in the coming six months. On 20 May, it will rise at 04:30 CEST and should be briefly visible (E, constellation of Aries). 

Saturn has re-emerged in the pre-dawn sky and will rise earlier as the month progresses (1st May at 04:08 CEST, 31 May at 02:14 CEST) in the constellation of Aquarius (SE).

Uranus will be at solar conjunction on 9 May 2023 and therefore, it won’t be visible. It will re-emerge in July.

Neptune will not be observable until end of June.

Phenomena not to miss in May

May is an excellent month to observe and take pictures of the Pinwheel Galaxy (Messier 101) in the constellation of Ursa Major. It’s at a distance of 22 mly from Earth and with an absolute diameter of 185’000 ly it is almost double the size of our Milky Way. Furthermore, there is a whole group of galaxies to be discovered – such as M 58, M 59, M 60, M 84, M 85, M 86, M 87, M 88, M 91, M 98 and M 100). In the constellation of Coma Berenices, again the Coma cluster is impressive and a great area to take pictures of. 

Penumbral lunar eclipse on 5 May 2023: The Moon will pass through the Earth’s shadow between 17:15 and 21:32 CEST. This penumbral lunar eclipse won’t be visible from most parts of central Europe, because the Moon will not be above the horizon at the time. It will be visible from Asia, Africa, Russia and Oceania. 

The night sky N-SE, 15 May 2023, 23:00 CEST, Bern, Switzerland:

The night sky S-W on 15 May 2023, 23:00 CEST, Bern, Switzerland:

The night sky SE-SW, 15 May 2023, 23:00 SAST, Cape Town, South Africa:

DateTime (CET)Phenomena
0400:55Spica 3.3°S of Moon (S)
05Early morningEta-Aquarid Meteor Shower
0519:24Pen. Lunar Eclipse; mag=0.964 (not visible from Central Europe)
07Early morningAntares close to the Waning Gibbous Moon (S)
0921:00Uranus in Conjunction with Sun 
13Early morningSaturn and the Waning Crescent Moon appear close (SE)
2320:00Venus 3°S of Waxing Crescent Moon
2422:00Mars 2°S of Waxing Crescent Moon
3021:00Mars at Aphelion: 1.67 AU


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