Skywatcher's Guide written by: Lucas Snyder (Flandrau Planetarium Specialist)
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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 (from 7 to 10 pm)
| Name / Designation | Apparent Magnitude (lower = brighter) | Distance (light-years) | Notes |
|---|---|---|---|
| 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 |
Solar System
Mercury passes between us and the Sun in mid-August but then appears in the morning sky for the last few days of the month. It will remain visible through the first couple weeks of September before disappearing again as it passes behind the Sun.
Venus may be visible in the evening sky throughout August and September getting gradually higher each night.
Mars is getting higher in the morning sky before sunrise, moving through Taurus and Gemini.
Jupiter comes up a little earlier each morning, eventually rising before midnight by the end of September. It is in the constellation Taurus.
Saturn rises a little earlier each evening, eventually coming up at sunset by the middle of September. It is in the constellation Aquarius.
Calendar of Night Sky Events
| Date | Event |
|---|---|
08/04/24 | New Moon. |
08/07/24 | Appulse of Mercury and Venus — Separated by 5.7°. |
08/12/24 | Peak of Perseids meteor shower. |
08/12/24 | First Quarter Moon. |
08/14/24 | Appulse of Mars and Jupiter — Separated by 0.3°. |
08/18/24 | Mercury at inferior conjunction. — Between us and the Sun. |
08/19/24 | Full Moon. |
08/26/24 | Last Quarter Moon. |
09/02/24 | New Moon. |
09/04/24 | Mercury at greatest western elongation. — Visible before sunrise. |
09/07/24 | Saturn at opposition. — Best time to see this ringed planet. |
09/10/24 | First Quarter Moon. |
09/17/24 | Full Moon and Partial Lunar Eclipse. — Visible from Tucson. |
09/20/24 | Neptune at opposition. — Best time to see our farthest planet. |
09/22/24 | Earth at Southward Equinox. — Beginning of our Fall. |
09/24/24 | Last Quarter Moon. |
09/30/24 | Mercury at superior conjunction. — Behind the Sun. |
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 (from 7 to 10 pm)
| 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 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 |
| 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 | 8 | 36" | 2,400 | planetary nebula |
| Messier 81 | Bode's Galaxy | 8.5 | 21' | 1,200,000 | spiral galaxy |
| Messier 57 | Ring Nebula | 8.8 | 1' | 2,300 | planetary nebula |
| Messier 82 | Cigar Galaxy | 9.5 | 14' | 1,200,000 | galaxy |
Frequently Asked Questions
What would living on a moon (instead of a planet) be like?
Aside from differences we see between planets such as atmosphere, gravity, magnetic field, etc, there are some factors that are unique to moons that we'd have to consider if we wanted to start a base or just go for a visit. One would be the planet the moon orbits. Most moons are much smaller than planets, so they don't make a big impact in our visibility of the sky if we're living on the planet. But if we are on a moon, the planet may take up a huge portion of the sky, drastically changing our view of both the daytime and nighttime sky. However, if the moon rotates synchronously, meaning one face always points towards the planet (which is common in our solar system), then one side of the moon would always have the planet in the sky, while the other side would never see the planet at all! So on that side, your view wouldn't be that much different from living on the planet itself.
If your moon orbits a planet with many other moons, it may be interesting to see the other moons grow and shrink in the sky depending on where they are in their orbits. It's similar to how from the Earth we can see the other planets grow and shrink through a telescope, but on a moon, you may not need a telescope to observe this.
The day/night cycle would work pretty much the same as what we're used to, although in general the periods would be longer due to the synchronous rotation I mentioned above. For example, on our Moon, a "day" would be the same length as a "month" on the Earth. But something else to consider would be eclipses. Solar eclipses happen a few times every year here on Earth, but they are confined to very narrow band of the surface. On the Moon, they happen about as frequently, but they cover the entire surface. There are some moons that experience solar eclipses much more frequently, even on a daily basis. Plus if you're on one of the moons of Jupiter, for example, this may take up a good fraction of your day. You would have sunlight in the morning and in the evening, but the middle of your day would be as dark as night. But again, if you happen to be on the side of a synchronous moon that never sees the planet, then you would not see eclipses either.
Seasons would also work pretty much the same as on a planet. The axial tilt of the moon compared to its path around the Sun (regardless of its path around the planet) determines the length of day and night and the incident angle of sunlight. But coming back to eclipses again, depending on the moon's orbital inclination around the planet, eclipses may be more frequent in certain seasons than others. Each moon's orbit has two "nodes" or points that line up with both the planet and the Sun. So whichever seasons these nodes happen to fall in would be a little colder due to the eclipses blocking the sunlight for part of the day.
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!
Date of publication: 2024