Skywatcher's Guide: April and May 2018


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  
Aldeberan 0.87 65  
Spica 0.98 262  
Pollux 1.16 38  
Deneb 1.25 3230  
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 is passing between us and the sun in early April, but will emerge in the morning sky by the end of the month. It will then begin to disappear again in late May.

Venus keeps rising higher and higher in the evening sky throughout April and May.

Mars rises earlier and earlier each night, eventually coming up before midnight by late May.

Jupiter rises a little after sunset in April, and then a little before sunset in mid and late May.

Saturn rises earlier and earlier each night, coming up before midnight by the end of April.

Jupiter Great Red Spot Transits during April and May (when the Flandrau dome is open)

Note: The GRS is visible on the disk of Jupiter for 50 minutes before and after meridian transit time.

Date Meridian Transit Time
04/28/18 08:13 PM
05/05/18 08:58 PM
05/10/18 08:05 PM
05/12/18 09:43 PM
05/24/18 09:36 PM

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Calendar of Night Sky Events

Date Event
04/01/18 Mercury at inferior conjunction. — Between us and the Sun.
04/02/18 Appulse of Mars and Saturn. — Separated by 1.3°.
04/08/18 Last Quarter Moon.
04/15/18 New Moon.
04/18/18 Uranus at conjunction. — Passing behind the sun.
04/22/18 Peak of Lyrids meteor shower.
04/22/18 First Quarter Moon.
04/25/18 Appulse of Mars and Pluto. — Separated by only 1.4°.
04/29/18 Mercury at greatest western elongation. — Visible in the morning before sunrise.
04/29/18 Full Moon.
05/07/18 Peak of Eta Aquariids meteor shower.
05/07/18 Last Quarter Moon.
05/08/18 Jupiter at opposition. — Best time to see our largest planet.
05/13/18 Appulse of Mercury and Uranus. — Separated by 2.2°.
05/15/18 New Moon.
05/21/18 First Quarter Moon.
05/29/18 Full Moon.

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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 33 Triangulum Galaxy 5.7 67' x 42' 3,000,000 spiral galaxy
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 82 Cigar Galaxy 9.5 14' 1,200,000 galaxy

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Frequently Asked Questions

What can we gain by studying astronomy?

Because space is "out there" (literally) it might be hard to see how looking into the cosmos can benefit humanity here on the Earth. But there are a lot of things we can gain by studying astronomy.

First off, Earth is of course located in space, so it is good to watch out for other things that might affect us — what we call space weather. This includes asteroids and comets that come near to us, as well as solar storms that might send charged particles our direction. There are various times in history where space weather has affected our technology, or even life itself. If we are aware of potential threats, we can at least think about ways we can protect ourselves, rather than just waiting for something to happen.

Another way that astronomy benefits us is by refining our knowledge of physics. The conditions on Earth are very tame in terms of pressures, temperatures, radiation, speed, gravity, etc, compared to a lot of other places in the universe. By looking at these types of places, we can see if the equations we use to model physics on Earth still hold true at these extremes. Pushing these equations to the limits can give us more insight into how things work and can fuel research into other areas such as particle physics, quantum mechanics, acoustics, hydrodynamics, etc.

Finally, one way that astronomy research has benefited humanity is through our technology. For example, the cameras we find in our smart phones are basically simplified versions of the cameras first developed for use with telescopes and satellites. Many things that were originally designed for use on spacecraft or by astronauts in space have found their way into everyday use. A quick internet search led me to this article with several examples.

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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  • Cornelius, Geoffrey. The Starlore Handbook: an Essential Guide to the Night Sky. San Francisco, CA: Chronicle, 1997. Print.
  • Ottewell, Guy. Astronomical Calendar 2012. Raynham, Mass: Universal Workshop, 2011. Print.
  • Ottewell, Guy. Astronomical Calendar 2013. Raynham, Mass: Universal Workshop, 2012. Print.
  • Ottewell, Guy. The Astronomical Companion. 2nd ed. Raynham, Mass: Universal Workshop, 2010. Print.
  • Astronomy Magazine. February 2013. Volume 41, No 2.
  • Astronomy Magazine. February 2013. Volume 41, No 3.
  • Sky & Telescope. February 2013. Volume 125, No 2.
  • Sky & Telescope. March 2013. Volume 125, No 3.

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