Skywatcher's Guide: August and September 2021

Skywatcher's Guide written by: Lucas Snyder (Flandrau Planetarium Operator)


Stars and Constellations

In August we can still see part of the spring sky at the beginning of the night after sunset. The bright star Spica in the constellation Virgo is low in the west-southwest. A little higher in the west is even brighter Arcturus in the constellation Boötes. The easily recognizable Big Dipper (Ursa Major) is also visible in the northwest. You can use two stars in the end of the bowl to find Polaris, the north star, which is the end of the handle of the Little Dipper (Ursa Minor). Next, high in the middle of the sky we see the summer constellations, with the three bright stars of the Summer Triangle being the most prominent. Vega is the highest and brightest of the three, with Deneb below towards the east and Altair to the southeast. Then Scorpius with the bright star Antares is visible to the south-southwest, and the "teapot" of Sagittarius is nearby towards the south. The summer Milky Way is prominent this time of year stretching all the way across the sky from south-southwest to north-northeast. Next, the fall sky is beginning to rise in the east at the beginning of the night. The "great square" of Pegasus is low towards the east and Andromeda is adjacent to the northeast. Cassiopeia is a little higher in the northeast, and appears as a "W" this time of year.

In September, Boötes is now low in the sky towards the west-northwest.  The Big Dipper is also very low in the northwest.  Polaris and the Little Dipper are of course still in the North.  Now Scorpius is low in the southwest, and we can see the Sagittarius "teapot" in the south-southwest.  The Summer Triangle is still up in the middle of the sky, and the summer Milky Way is still a prominent streak across the sky.  Next, Pegasus and Andromeda are higher in the east, and you might be able to find the Andromeda Galaxy. Cassiopeia is higher in the northeast and is starting to rotate to a "3" orientation. Finally, below that you may see Perseus along the horizon at the beginning of the night.

Interesting Stars Visible in August and September (during observatory hours)

Name / Designation Apparent Magnitude
(lower = brighter)
Arcturus -0.05 36.7  
Vega 0.03 25  
Altair 0.76 17  
Spica 0.98 262  
Fomalhaut 1.16 25  
Markab 1.25 140  
Deneb 1.25 3230  
Polaris 1.97 431  
Alpheratz or Sirrah 2.07 97  
Mirach 2.07 199  
Algol 2.09 93 variable star
Denebola 2.14 36.2  
Enif 2.38 670  
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 passing behind the Sun at the beginning of August, but will become visible again in the evening sky in September.

Venus is getting higher in the western sky each evening after sunset.

Mars is getting closer to the Sun and will be very difficult to see after the beginning of August.

Jupiter is visible in the east after sunset, getting a little higher each night in the constellation of Capricornus.

Saturn is just a little above Jupiter, also in Capricornus.

Jupiter Great Red Spot Transits during August and September (when the Flandrau observatory 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
08/21/21 08:02 PM
08/28/21 08:47 PM
09/02/21 07:54 PM
09/04/21 09:32 PM
09/09/21 08:40 PM
09/16/21 09:25 PM

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Calendar of Night Sky Events

Date Event


Mercury at superior conjunction. — Passing behind the Sun.


Saturn at opposition. — Best time to see this ringed planet.


New Moon.


Peak of Perseids meteor shower. — Learn more about it here


First Quarter Moon.


Appulse of Mercury and Mars — Separated by 0.07°.


Jupiter at opposition. — Best time to see our largest planet.


Full Moon.


Last Quarter Moon.


New Moon.


First Quarter Moon.


Mercury at greatest eastern elongation. — Visible after sunset.


Neptune at opposition. — Best time to see our farthest planet.


Full Moon.


Earth at Southward Equinox. Beginning of our Fall.


Last Quarter Moon.

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Deep Sky

There are many deep sky objects we can see since the summer Milky Way is high in the sky.  There are many open star clusters that can be seen with only binoculars scanning this part of the sky.  For example we have the Butterfly Cluster (M6) and Ptolemy's Cluster (M7) near the tail of Scorpius.  Further north there is the Wild Duck Cluster (M11) in the faint constellation of Scutum between Sagittarius and Aquila.  There is also the asterism of the Coathanger between Aquila and Cygnus in the fainter constellation of Vulpecula.  Next, heading towards the west we can see the Coma Star Cluster in the constellation of Coma Berenices, which is even visible naked-eye.  The Pleiades (M45) will be visible later in the night, after midnight.

There are a several globular clusters we can see as well, as the center of our galaxy is the highest it gets for the year.  Near the bright star Antares in Scorpius lies the globular cluster M4.  In Sagittarius we also have the Teapot Cluster (M22).  Of course we have the famous Hercules globular (M13) high in the east.  Also, M15 is visible in the east near the head of Pegasus.

For nebulae, we have several in the plane of the galaxy, one of which is the Swan Nebula (M17) in Sagittarius, also known as the Omega Nebula.  There is also the Lagoon Nebula (M8) nearby and the North America Nebula (C20) further north in Cygnus.  For planetary nebulae we have the Ring Nebula (M57) in Lyra, the Dumbell Nebula (M27) in Vulpecula, and the Blue Snowball (C22) in Andromeda.

And now the galaxies:  Although the Big Dipper is getting lower in the sky, you may still be able to find some of the galaxies in this part of the sky.  We have the Whirlpool Galaxy (M51) and the Pinwheel Galaxy (M101) near the handle, and the Cigar Galaxy (M82) and Bode's Galaxy (M81) near the bowl.  The spectacular Andromeda Galaxy (M31) is now coming up in the northeast, along with the nearby Triangulum Galaxy (M33).

Interesting Deep Sky Objects to Observe during August and September (during observatory hours)

Designation Name Apparent Magnitude Apparent Size Distance

Messier 31

Andromeda Galaxy


3° x 1°


spiral galaxy

Messier 33

Triangulum Galaxy


67' x 42'


spiral galaxy

Messier 3

(in Canes Venatici)




globular cluster

NGC 7293 Helix Nebula 7.3 16' 450 planetary nebula
Messier 27 Dumbbell Nebula 7.4 8' × 6' 1,250 planetary nebula

NGC 7009

Saturn Nebula




planetary nebula

Messier 81

Bode's Galaxy




spiral galaxy

Messier 57 Ring Nebula 8.8 1' 2,300 planetary nebula

Messier 82

Cigar Galaxy





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Frequently Asked Questions

How do astronomers get such colorful pictures of galaxies and nebulae?

If you've ever looked at deep sky objects such as galaxies and nebulae through a telescope, many people are disappointed to find that they only seem to be in black and white.  So if they just appear to be shades of grey to our eyes, why are photographs so colorful?

There are two main reasons for this.  One is that our eyes are not good at distinguishing colors in low-light settings.  You have probably heard that your eye uses rod and cone cells in your retina to detect light.  In bright light, your cones are doing most of the work, and there are actually three different types of cone cells which allows our eye to distinguish different colors.  However, in low light settings, our rods are doing most of the work, and they cannot distinguish color.  So that is why the colors of these deep sky objects look so bland to our eyes.  While they do in fact have colors, our eyes are just not picking them up very well.

Second, cameras have a few advantages over our eyes.  One is that our eye (together with our brain) creates an image based on only a fraction of a second of information.  Cameras on the other hand can accumulate light for many seconds or even minutes to create a single image.  This allows them to pick up much fainter details than what our eyes can.  Plus, cameras essentially store each color as a separate image.  Many cameras have built-in RGB (true-color) filters that approximate the wavelengths our eyes can see, but there are other (false-color) filters such as infrared, H-alpha, and O-III that can be used as well.  When these colors are combined, they can be adjusted independently to bring out certain features that may be too subtle or even invisible to our eyes, and greatly increase the color saturation in the image compared to what our eyes can perceive.

So while colorful images from Hubble or other big telescopes don't look anything like what we see with our eyes, they are far from "fake".  They are picking up real light from these distant objects and processing it in a way that gives us much more information than what our eyes alone can.  When you see a colorful image, it is a good habit to read the caption to see if it is true-color or false-color, and what the different colors might represent.  For stars, color is directly related to temperature, but for nebulae, color is more closely related to composition.  For example, hydrogen gas usually appears red or pink, oxygen appears bluish-green, and sodium appears yellowish.  So these images are not just pretty images to look at, but scientifically valuable tools that help us learn about the distant regions of our universe.

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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