The University of Arizona

Skywatcher's Guides

Flandrau’s Observatory is operated entirely by volunteers. Please call ahead to see if the observatory is open (generally Thurs-Sat 7pm – 10pm). Our astronomer volunteers will help you experience the 16-inch telescope as well as answer your questions about the night sky.

Written by: Lucas Snyder (Flandrau Planetarium Operator)
Images contributed by: Tim Van DevenderAlistair Symon (Flandrau Telescope Operators), Nine Planets, and Students for the Exploration and Development of Space (SEDS)

Navigationphoto by Tim Van Devender

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

 

Name / Designation

Apparent Magnitude
(lower = brighter)

Distance

(light-years)

Notes

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

 

Altair

0.76

17

 

Aldeberan

0.87

65

 

Spica

0.98

262

 

Pollux

1.16

38

 

Markab

1.25

140

 

Deneb

1.25

3230

 

Castor

1.58

52

 

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

Mars is coming up in the morning just before sunrise, a little earlier each day.

 

Venus is passing between us and the sun in August, but will be visible again in the morning in September.

 

Jupiter is now passing behind the sun, but will begin emerging in the morning sky by the end of September.

 

Saturn is slowly heading further west at the beginning of the night, still near the claws of Scorpius.

 

Mercury emerges from the glare of the sun in late August and will be visible in the evening after sunset. But by late September it will be lost again as it heads between us and the sun.

 

Calendar of Night Sky Events

 

08/06/15

Mercury and Venus in conjunction. Separated by 7.8°

08/06/15

Last Quarter Moon.

08/07/15

Mercury and Jupiter in conjunction. Separated by only 0.5°.

08/13/15

Peak of Perseids meteor shower.

08/14/15

New Moon.

08/15/15

Venus at inferior conjunction. Between us and the sun.

08/22/15

First Quarter Moon.

08/26/15

Jupiter at conjunction. Passing behind the sun.

08/29/15

Full Moon.

08/31/15

Neptune at opposition. Best time to see this distant planet, although it will only be visible with a telescope.

09/02/15

Venus and Mars in conjunction. Separated by 8.7°.

09/03/15

Comet SOHO at brightest. Probably not visible since it will be very close to the sun.

09/04/15

Mercury at greatest eastern elongation. Visible in the evening after sunset.

09/05/15

Last Quarter Moon.

09/12/15

New Moon and Partial Solar Eclipse. Not visible from Tucson.

09/21/15

First Quarter Moon.

09/23/15

Earth Southward Equinox. Beginning of our autumn.

09/27/15

Full Moon (Supermoon) and Total Lunar Eclipse. Will be just beginning at moonrise.

09/30/15

Mercury at inferior conjuction. Between us and 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

Designation

Name

Apparent Magnitude

Apparent Size

Distance

(light-years)

Type

Messier 45

Pleiades

1.6

110'

440

open cluster

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 33

Triangulum Galaxy

5.7

67' x 42'

3,000,000

spiral galaxy

NGC 7009

Saturn Nebula

8

36"

2,400

planetary nebula

Messier 81

Bode's Galaxy

8.5

21'

1,200,000

spiral galaxy

Messier 82

Cigar Galaxy

9.5

14'

1,200,000

galaxy

 

Frequently Asked Questions – Why don't we see comets very often?

There are a little over 5000 comets discovered so far, with possibly a trillion more undiscovered out there.  If there are so many, why can't we see them?

 

Comet nuclei (the solid portions of comets) are small.  The largest one known is only around 100 km across, and most are around 10 km or so.  At these sizes, they would have to be extremely close to us to be able to spot.  That being said, however, when they get close to the sun and heat up, volatile molecules vaporize and create a sort of atmosphere called a coma that can be larger than Jupiter or even the sun!  Plus, the coma can get stretched out into a tail that can be more than half a billion km long.  So the size alone doesn't explain why we can't see them.

 

The main reason we don't see them very often is that most of them are in huge elliptical orbits so that it takes them many thousands of years to make a full orbit.  So they may be visible for a few weeks or so, and then return to obscurity for millenia.  There are comets with shorter periods, but even 200 years is still considered short-period.  Long-period comets may take over a million years.  A few comets are on hyperbolic orbits that will take them out of our solar system, never to return.

 

The main reservoir of comets is called the Oort Cloud.  This hasn't been observed directly, but has been proposed to explain the origin of the longer period comets.  The Oort cloud may extend over a light-year from our sun, thousands of times the size of the orbit of Neptune.  When comets are this far away, they have no coma or tail and are thus very tiny and nearly impossible to detect.  (This is why we think there could be a trillion more left to be discovered).

 

So there's our answer.  It is the fact that they are so far away, coupled with their small sizes that we can not see them most of the time.  Several comets are detected every year, but only maybe one or two may be bright enough to approach naked-eye visibility.  And only one per decade or so will be considered a "great comet" easily visible to anyone who casually glances up at the sky.

 

If you ever get to see one of these great comets, it truly is a rare treat.  I have seen several comets through a telescope, but the spectacular comet Hale-Bopp, visible when I was in high school, stands out in my memory as a truly memorable sight.  The appearance of new comets is very difficult to predict, so we'll just have to wait and see when the next one will come by.

 

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!

 

Table of Images (Click on an image to expand)

Sketches and Images - Image Credit (Tim Van Devender)

Mars

Mars

Saturn

Saturn

Jupiter

Jupiter

The Moon

The Moon

Jupiter and Io Moon Shadow

Jupiter and Io Moon Shadow

Messier 45 (Pleiades)

M45

NGC 884 and NGC 869 - Perseus Double Cluster

NGC 884 and NGC 869 - Perseus Double Cluster

NGC 2024 - The Horsehead and Flame Nebulae

NGC 2024 - The Horsehead and Flame Nebulae

NGC 2237 - The Rosette Nebula

NGC 2237 - The Rosette Nebula

NGC 2264

NGC 2264

Images from Alistair Symon
Messier 27 (Dumbbell Nebula)

M27

Mssier 31 (Andromeda Galaxy)

M31

Messier 33 (Triangulum Galaxy)

M33

Messier 45 (Pleiades)

M45

Messier 57 (Ring Nebula)

M57

Images from Nine Planets
Jupiter

Jupiter

The Moon

The Moon

Images from SEDS
Messier 13 (Hercules Globular Cluster)

M13

Messier 15

M15

Messier 27 (Dumbbell Nebula)

M27

Messier 31 (Andromeda Galaxy)

M31

Messier 33 (Triangulum Galaxy)

M33

Messier 44 (Beehive Cluster)

M44

Messier 45 (Pleiades)

M45

Messier 57 (Ring Nebula)

M57

NGC 7009 (The Saturn Nebula)

NGC 7009

NGC 7293 (The Helix Nebula)

NGC 7293

 

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.