Skywatcher's Guide: June and July 2021

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June Solar Eclipse

While this annular solar eclipse won't be visible from Tucson, we can view live streams from those locations that can. Tune in to sites such as Time & Date on June 10th starting at 1:12am MST to check it out!

Stars and Constellations

In June, the spring sky is now prominent overhead, along with the familiar Big Dipper.  The Big Dipper is high in the north, 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. Then Hercules is just below towards the east.  Next, Leo the lion is very high in the west, with the constellation Virgo nearby to the south.  A few winter constellations are still visible, now vert low in the west.  Castor and Pollux, the heads of Gemini the twins, are the most prominent, to the west-northwest.  The summer sky is now just starting to come up at the beginning of the night.  The bright star Vega in the constellation Lyra the harp is towards the east-northeast.  In the southeast we have the constellation Scorpius the scorpion, with the bright star Antares.  Further to the south we can also see the constellations of Centaurus and Lupus the wolf right along the horizon.

In July, the last of the winter constellations are now gone, and the spring constellations are beginning to head to the west.  The summer constellations are now mostly up in the east.  We can easily see all three stars in the Summer Triangle, Vega being the highest in the east-northeast, Deneb a little lower to the northeast, and Altair to the east.  To the southeast we can see the Teapot of Sagittarius near the tail of Scorpius.  Also, to the north-northeast we can see the W of Cassiopeia the queen.

Interesting Stars Visible in June and July (during observatory hours)

Name / Designation Apparent Magnitude
(lower = brighter)
Distance
(light-years)
Notes
Arcturus -0.05 36.7  
Vega 0.03 25  
Capella 0.08 42  
Procyon 0.4 11  
Altair 0.76 17  
Spica 0.98 262  
Pollux 1.16 38  
Markab 1.25 140  
Deneb 1.25 3230  
Regulus 1.36 77 means "Little King"
Castor 1.58 52  
Polaris 1.97 431  
Alpheratz or Sirrah 2.07 97  
Denebola 2.14 36.2  
Enif 2.38 670  
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 passes between us and the Sun in the first half of June, but will be visible in the eastern sky before sunrise at the end of the month and for most of July.

Venus is now visible in the western sky after sunset, getting higher and higher each night.

Mars is getting lower in the western sky after sunset, moving from Gemini into Cancer.

Jupiter rises late in the evening, but slightly earlier each night.  It is in the constellation of Aquarius.

Saturn also comes up in the evening, but by the end of July will be up right after sunset. It is in the constellation of Capricornus.

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Calendar of Night Sky Events

Date Event
06/02/21 Last Quarter Moon.
06/10/21 New Moon and Annular Solar Eclipse. — Not visible from Tucson.
06/10/21 Mercury at inferior conjunction. — Between Earth and the Sun.
06/17/21 First Quarter Moon.
06/20/21 Earth at northern solstice. — Beginning of our Summer.
06/24/21 Full Moon.
07/01/21 Last Quarter Moon.
07/04/21 Mercury at greatest western elongation. — Visible before sunrise.
07/05/21 Earth at aphelion. — Our farthest distance from the Sun.
07/09/21 New Moon.
07/13/21 Appulse of Venus and Mars. — Separated by 0.5°.
07/17/21 First Quarter Moon.
07/17/21 Pluto at opposition. — Best time to look for this dwarf planet.
07/23/21 Full Moon.
07/27/21 Peak of Delta Aquariids meteor shower.
07/31/21 Last Quarter Moon.

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Deep Sky

There are several open star clusters we can see this time of year. First, Coma Berenices (Bernice's Hair) is high in the west near the tail of Leo. Next, there is the Ptolemy cluster (M7) and the Butterfly (M6) in the southeast near the tail of Scorpius. Also nearby is the Wild Duck (M11) in the constellation of Scutum.

Now that the Milky Way is coming up, there are several globular clusters we can see. M3 is high in the west, in the constellation Boötes. Nearby, the famous Hercules Globular (M13) is high in the east. We also have M5 high in the south in the constellation of Serpens. Finally, for those with a clear horizon, the amazing Omega Centauri (C80) is visible low to the south.

For nebulae, we can see the Swan (M17), the Lagoon (M8), and the Trifid (M20) to the southeast in the constellation Sagittarius. The Eagle (M16) is nearby in the constellation of Serpens. The North America nebula is also in the northeast in Cygnus. For planetary nebulae, we have the Owl (M97) in Ursa Major high in the northwest. We also have the Dumbbell (M27) in the west-northwest in the constellation of Vulpecula and the Ring (M57) nearby in Lyra.

And now the galaxies: In Ursa Major to the northwest 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 Southern Pinwheel (M83) is to the southwest in the constellation Hydra. The Sombrero Galaxy (M104) is nearby in the constellation Virgo.

Interesting Deep Sky Objects to Observe during June and July (during observatory hours)

Designation Name Apparent Magnitude Apparent Size Distance
(light-years)
Type
Messier 31 Andromeda Galaxy 3.4 3° x 1° 2,900,000 spiral galaxy
Messier 44 Beehive Cluster 3.7 95' 577 open cluster
Messier 3 (in Canes Venatici) 6.2 18' 34,000 globular cluster
Messier 27 Dumbbell Nebula 7.4 8' × 6' 1,250 planetary nebula
NGC 7009 Saturn Nebula 8 36" 2,400 planetary nebula
Messier 81 Bode's Galaxy 8.5 21' 12,000,000 spiral galaxy
NGC 3242 Ghost of Jupiter 8.6 25" 1,400 planetary nebula
Messier 57 Ring Nebula 8.8 1' 2,300 planetary nebula
Messier 82 Cigar Galaxy 9.5 14' 12,000,000 galaxy

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Frequently Asked Questions

What will happen to our Sun when it dies?

Our Sun is a star, and it creates energy by fusing hydrogen into helium in its core.  While it has plenty of hydrogen to keep it going for a while, it won't last forever and our Sun will eventually die.  So what will this look like, and how long does it have left?

Our Sun is currently in what's called the Main Sequence, which is where it will spend most of its life, fusing hydrogen as it is now.  But gradually helium will replace hydrogen in the core, and hydrogen fusion will move slightly outward to a shell surrounding the core.  The Sun's surface will slowly cool and expand into what's called a subgiant.

As the helium core grows, it will eventually reach a point where it collapses under its own weight, greatly increasing the pressure and thus the rate of fusion in the surrounding hydrogen shell.  The sudden increase in power will quickly expand the Sun into a red giant, without changing the surface temperature that much.

As the helium continues to build up, it will approach the pressure and temperature necessary to begin fusing helium into carbon.  It ignites very quickly in what's called a helium flash, and the core reinflates.  The hydrogen shell inflates along with it, but decreases in pressure, meaning that the overall energy output of the Sun will decrease, and thus the radius will shrink while the surface temperature increases.  This phase is called the horizontal branch.

Next, just as the helium replaced hydrogen during the main sequence, carbon will replace helium in the horizontal branch.  Helium fusion begins to be pushed outwards into a shell just below the hydrogen shell.  The Sun's surface will begin cooling again while increasing in size.  This phase is called the asymptotic giant branch, as it again approaches the appearance it had during the red giant phase.  In the asymptotic giant branch, the Sun can switch between having hydrogen fusion and helium fusion be the dominant source of energy output, so it may also fluctuate in brightness and surface temperature during this phase.

Hydrogen and helium fusion will slow down as the carbon core of the Sun grows, but the Sun will never reach the point of sustaining carbon fusion.  So once fusion has run its course, the Sun will cease to be a star and become a stellar remnant.  The solar wind continues to remove mass from the Sun until eventually the core is exposed.  The hot core emits ultraviolet light which makes the surrounding material glow in what we call a planetary nebula.

Finally, the planetary nebula gradually fades out leaving behind the naked core known as a white dwarf.  The white dwarf very slowly cools until it will eventually become a black dwarf, just a cold sphere of carbon floating in space for the rest of time.

Our Sun has an estimated lifetime of around 10 billion years, and we think it is about halfway through that now.  The next phase won't start for at least another billion years or two, so we humans don't need to worry about it too much quite yet.  But once the Sun gets to the red giant phase, that's when time will be up for life on Earth, and probably even the Earth itself.

(Many thanks to Astronomy Professor Tom Fleming for proofreading this for me!)

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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Bibliography

  • 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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Date of publication:
2021