Skywatcher's Guide: April and May 2023



Stars and Constellations

In April, the spring sky is now prominent in the east, along with the familiar Big Dipper.  The Big Dipper is high in the northeast, and the two stars at the end of the bowl can be used to find Polaris, our north star.  Also, the handle can be used to "arc to Arcturus", a bright star in the constellation Boötes. Next, Leo the lion is very high in the east, approaching the middle of the sky now, with the constellation Virgo just below.  The winter constellations are also visible, now in the west.  Taurus the bull is getting lower in the west, near Orion the hunter to the west-southwest.  Canis Major (the big dog), along with the bright star Sirius, is also getting low in the southwest.  Gemini the twins is a little higher in the west, along with Auriga the charioteer in the west-northwest and Canis Minor (the little dog) in the southwest.  The winter Milky Way is now getting lower in the west as well.  Far to the south we can see some constellations making up part of Jason's Argo Navis, which we only get to see briefly since it is so far south.  Finally, there is still a small portion of the fall sky still visible just for the first hour or so of the night.  Cassiopeia the queen is in the north-northwest, and Perseus the hero is in the northwest.

In May, the winter constellations are lower in the west, and Orion, Taurus, and Canis Major are already in the process of setting at the beginning of the night, along with Cassiopeia and Perseus to the northwest.  The spring constellations are higher now, and we can see the rest that weren't up this time last month.  Hercules is below Boötes in the east-northeast.  Some of the summer constellations are also getting ready to come up and will be visible a few hours after sunset.

Interesting Stars Visible in April and May (during observatory hours)

Name / Designation Apparent Magnitude
(lower = brighter)
Sirius -1.44 8.6  
Arcturus -0.05 36.7  
Vega 0.03 25  
Capella 0.08 42  
Rigel 0.18 770  
Procyon 0.4 11  
Betelgeuse 0.45 427  
Aldebaran 0.87 65  
Spica 0.98 262  
Pollux 1.16 38  
Regulus 1.36 77 means "Little King"
Castor 1.58 52  
Polaris 1.97 431  
Algol 2.09 93 variable star
Denebola 2.14 36.2  
Almak 2.1 / 5.0 & 6.3 355  triple star system w/ 64 yr orbit
Albireo 3.2 / 5.8 & 5.1 390 / 380  possibly a triple star system
Eta Cassiopeiae 3.5 / 7.4 19 480 yr orbit

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Solar System

Mercury will be visible in the evening sky for much of April, but will be passing between us and the Sun at the beginning of May.  It will then be visible in the morning sky in the second half of the month.

Venus is bright and high in the western sky throughout April and May.

Mars starts April nearly overhead at the beginning of the night, slowly creeping closer to the west.  It is moving through Gemini and Cancer.

Jupiter passes behind the Sun in April and will emerge in the morning sky in May.  It is moving through Pisces.

Saturn stays in Aquarius, rising in the early morning during April and getting higher and higher every day.

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Calendar of Night Sky Events

Date Event
04/05/23 Full Moon.
04/11/23 Jupiter at conjunction. — Passing behind the Sun.
04/11/23 Mercury at greatest eastern elongation. — Visible in the evening sky.
04/13/23 Last Quarter Moon.
04/19/23 New Moon and Hybrid Solar Eclipse. — Not visible from Tucson.
04/22/23 Peak of Lyrids meteor shower.
04/27/23 First Quarter Moon.
05/01/23 Mercury at inferior conjunction. — Passing between us and the Sun.
05/05/23 Peak of Eta Aquariids meteor shower.
05/05/23 Full Moon and Penumbral Lunar Eclipse. — Not visible from Tucson.
05/09/23 Uranus at conjunction. — Passing behind the Sun.
05/12/23 Last Quarter Moon.
05/19/23 New Moon.
05/27/23 First Quarter Moon.
05/28/23 Mercury at greatest western elongation. — Visible in the morning sky.

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Deep Sky

The winter Milky Way is now getting low in the west, but there are still several interesting objects we can see here.  The Pleiades (Seven Sisters, M45) is close to the west-northwest horizon right next to the Hyades (C41), which makes the face of Taurus the bull.  The constellation Auriga is a little bit higher, where we can see M36, M37, and M38, which are visible with binoculars.  The Double Cluster (C14) in Perseus is low in the north-northwest.  Higher in the sky we have the Beehive (Praesepe, M44) in Cancer the crab and Coma Berenices (Bernice's Hair) near the tail of Leo.

We are now beginning to see some globular clusters coming up in the east.  M3 is towards the east, in the constellation Boötes.  Nearby, the famous Hercules Globular (M13) is low to the east-northeast.

For nebulae, we have the spectacular Orion Nebula (M42) now now getting low to the west-southwest. This is the closest star-forming region to our solar system.  We also have some good planetary nebulae, which come from dying stars.  The Eskimo (C39) in Gemini is high in the west, the Owl (M97) in Ursa Major is high in the northeast, and the Ghost of Jupiter (C59) is to the south in the constellation Hydra.

And now the galaxies:  In Ursa Major to the north we have Bode's Galaxy (M81) and the Cigar Galaxy (M82), close enough to be seen together in a low-power telescope.  Nearby in the constellation Canes Venatici we have the Whirlpool (M51), which is a pair of colliding galaxies.  The Pinwheel Galaxy (M101) is also nearby near the handle of the Big Dipper.  Then the Sombrero Galaxy (M104) is in the southeast in the constellation Virgo.

Interesting Deep Sky Objects to Observe during April and May (during observatory hours)

Designation Name Apparent Magnitude Apparent Size Distance
Messier 45 Pleiades 1.6 110' 440 open cluster
Messier 44 Beehive Cluster 3.7 95' 577 open cluster
Messier 42 Orion Nebula 4 85' x 60' 1400-1600 diffuse nebula
Messier 3 (in Canes Venatici) 6.2 18' 34,000 globular cluster
Messier 81 Bode's Galaxy 8.5 21' 1,200,000 spiral galaxy
NGC 3242 Ghost of Jupiter 8.6 25" 1400 planetary nebula
Messier 57 Ring Nebula 8.8 1' 2,300 planetary nebula
Messier 82 Cigar Galaxy 9.5 14' 1,200,000 galaxy

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Frequently Asked Questions

Why are some things in space round while others are flat?

You probably noticed that the planets are all round, along with stars and other large objects.  There are also some things that are flat, such as Saturn's rings, our solar system, and the entire Milky Way.  Of course there are some things that don't fit into either of these categories, but these are two pretty common shapes we see in space.

Gravity is the dominant force when you are dealing with large objects and vast distances.  For planets, gravity is what pulls things together, equally in all directions, leading to this spherical shape.  Even if it starts off lumpy, the larger it gets the more gravity wants to smooth it out into a perfect sphere.  It's easy to see this with gasses and liquids, but even solids have a limit to how much force they can withstand until they deform.  Small objects can stay lumpy because their gravity is not strong enough to change their shape, but once they reach a certain size that round shape is inevitable.  This now is actually one of the requirements for what makes a planet.

Ok, but what about the flat shape?  This is a combination of gravity and spin.  I like to think of it like making pizza dough.  When you spin the dough it naturally tends to flatten out.  This is most noticeable in space when an object is made of a lot of smaller pieces.  For example, the rings of Saturn are made of countless tiny fragments spread into an extremely thin disk.  They pull on each other gravitationally just a tiny bit as they all orbit around Saturn.  If any of them wander out of that plane, they will feel a pull bringing them back.  This correction is what maintains that flat shape over long periods of time.

There are certainly other factors that can affect the shape of something in space, but now you know what causes the two most common shapes we see.

If you have any questions you'd like me to answer in the next issue of SWG, please let me know.  I'm also happy to take suggestions or comments, and also pictures if you'd like to send them.  Happy viewing!

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Date of publication: 2022