Self-Guided Night Sky Tour: Sept. 21, 2020

Milky Way

Important: The International Space Station is only visible from 7:32 to approximately 7:42 p.m. A clear view toward the north is critical.

Welcome to your self-guided September Night Sky Tour courtesy of HCT volunteer astronomer Michael Payne.

If you want to see the International Space Station make sure you have identified what direction north is and you have identified the Big Dipper and the North Star before the scheduled appearance of the International Space Station.

The International Space Station will appear as a bright, moving star.  It will rise approximately below the Big Dipper and arc towards the Little Dipper and then move towards the constellations Cassiopeia and Perseus as it sets in the northeast.

Directions for locating these constellations are below, but the International Space Station should be visible and obvious even if you are facing north and haven’t identified any constellations. 

Thanks to HCT volunteers Earline Rubel and Patti Smith for the heads up to keep our eyes to the sky for the International Space Station.

Increase your chances of having a successful night by following these guidelines.

  1. Find a location away from streetlights and as open to the horizons as possible. Red River Beach in South Harwich is recommended. Remember to practice social distancing. Your yard can work well, too, but it might limit what parts of the sky are visible.
  2. Use the September Evening Sky Map at this link to orient yourself. You will want to have the direction that you are facing at the bottom of the map.
  3. Avoid using a white light flashlight, either traditional handheld or your phone’s light, to read the map. The bright light will dazzle your eyes and prevent your eyes from becoming adapted to the dark. 
  4. If you have it, use red cellophane to cover your flashlight lens so the map is just barely legible. Don’t worry, your eyes will adapt to the darkness. When your eyes are dark adapted you will be able to see fainter stars and the shapes of the constellations will match those in the Sky Map much better.
  5. Be patient. It will take some time before the shapes of the constellations emerge from what first appears to be the chaos of the night sky.  The autumn constellations are the year’s faintest constellations, so take some time to follow the map from what you have identified to what you are trying to locate.

Good luck!

Find North

In order to begin our tour, we first have to face north and then turn the map so north is at the bottom of sky map when we hold it in front of us.

Here’s one way to find north at night.  If you know where Nantucket Sound is—that’s on the southside of the Cape — then to face in a general northerly direction, turn so the Sound is at your back.

Now let’s find the North Star, Polaris, the star that in the Northern Hemisphere is always aligned with true North.

Ursa Major and North Star

The Big Dipper and Ursa Major

As you look up in the northern night sky you will see a very bright pattern of seven stars that looks like an old-fashion water ladle.  This is called The Big Dipper. These will be the brightest group of stars in the northwest above the northern horizon.

During the next three months the Big Dipper will appear to be at its lowest in the northern sky, so it may be difficult to see if your view is blocked by trees or houses in this direction.  If it is, you will be able to use the constellation Cassiopeia to locate the North Star.

Use the Sky Map to judge how high these stars are in the sky.  Turn the Sky Map so the direction North is at the bottom of the map. Now locate the Big Dipper on the map at approximately the 7:00 position. Once you find this group of stars on the map, then you will be able to move around the sky using the map very easily. At this time of year, the Dipper appears to be pointed down towards the horizon, with the ladle part of the Dipper nearest the horizon. The Big Dipper is part of a larger constellation call Ursa Major (The Big Bear).  The Dipper part of the constellation represents the Bear’s midriff and hindquarters and its legs extend from the bottom of the cup part of the dipper.  Its feet are marked by three pairs of fainter stars.  The bear’s forequarters and extend beyond the front of the dipper.

To find the North Star draw a line between the two stars at the end of the ladle and then extend it about five times that length.  The only bright star in the sky where that ends is the North Star.  It is not the brightest star, but it is always in that location very close to the North Celestial Pole. The Sky Map shows which two stars to use.

Make sure you take the time to correctly identify the North Star.  A little practice and it will pop out from the night sky.  Be sure, too, to locate it on the map.

Ursa Minor (The Little Bear)

The North Star is in another constellation called Ursa Minor (The Little Bear) and it’s also called the Little Dipper.  It is much fainter than the Big Dipper and the shape isn’t as obvious as the Big Dipper, but if you are in a dark location you should be able to see it. Locate it on the map and then locate it in the sky, curving down towards the Big Dipper. A pair of brighter stars between the North Star and the Big Dipper known as The Guardians are in the ladle part of the Little Dipper.

Ursa Major and Minor are referred to as Circumpolar Constellations because they always circle the North Star and never set.  While the North Star appears to never move, all other stars seem to circle around it, sometimes above, sometimes below and to the right or left.


Cassiopeia the Queen

An easy circumpolar constellation to locate is Cassiopeia.  A group of 5-6 stars in the 2 o’clock position from the North Star looks like the letters “M” or “W” tuned on their side.  This is the constellation Cassiopeia. The constellation represents a woman sitting in a chair.

Cassiopeia was the mother of the maiden Andromeda and the wife of Cepheus.  Cassiopeia claimed she was more beautiful than a goddess.  The goddess, to teach Cassiopeia a lesson in humility, chained her daughter Andromeda to rock in the sea and sent a monster to devour her. Fortunately, the hero Perseus rescued her and killed the monster using the gorgon Medusa’s head to turn it to stone.  The gods commemorated these events by placing constellations of these people in the night sky.

Cassiopeia is a bright, obvious constellation.  So, if you haven’t been able to find the Big Dipper you should be able to see Cassiopeia. To locate the North Star using Cassiopeia and assuming it is located at the 2 o’clock position on a clockface, project a line towards the center of the clock face.  The first single brighter star you encounter will be the north star.  Again, make use of your map.

Cepheus the King

At about the 1 o’clock position from the North Star, above and to the left of Cassiopeia, is the constellation Cepheus. Look for a fainter group of stars in the shape of a pentagon, a square with a triangle on top it leaning to the left.  This constellation represents the father of Cepheus and the husband of Cassiopeia. 

The Eastern Sky

Turn the Sky map 90 degrees so the direction marked East is at the bottom of the page and turn yourself 90 degrees as well.  Now you are facing east. Cassiopeia should be to your left.

Perseus the Hero

Directly below Cassiopeia is a group of bright stars rising in the north-east.  This is the constellation Perseus. Its stars represent the hero who rescued Andromeda from the clutches of a sea monster. The brightest star in this group is called Algenib, derived from the Arabic word for “The Side.” A group of stars stretching towards Cassiopeia from Algenib represents Perseus’ upraised sword. A line of stars running towards the east from Algenib and ending in a star somewhat fainter than Algenib represents Perseus holding the head of the Gorgon Medusa in his hand.  The name of the star that represents the head of Medusa is called Algol from the Arabic al-Ghul, the Demon or Ghoul. Algol is a variable star, that is, its brightness varies by a significant amount over the course of approximately three days.  This is because it is a double star, two stars orbiting one another, and when the fainter component eclipses the brighter one the combined brightness of the stars dim.

The stars below Algenib represent the legs of Perseus.  By next month the constellation will be ideally placed for viewing.

The Great Square of Pegasus

Moving directly from the right of Cassiopeia to almost due east are four bright stars that mark the angles of a large square.  This is called the Great Square of Pegasus.  Pegasus is the winged horse of Greek mythology that was formed from the drops of blood that fell from Medusa’s head as Perseus flew over the sea to rescue Andromeda. The square represents Pegasus’ body. His head and wings extend out between two uppermost stars of the square in three lines of faint stars.

Andromeda the Maiden

Andromeda shares a star in Pegasus’ Great Square, the northernmost star in the square and the one closest to Cassiopeia.  This star is named Alpheratz, derived from the Arabic phrase for “The Horse’s Navel.” From Alpheratz, six stars in two lines of three stretch back towards Perseus.  These stars represent the arms and legs of Andromeda. A little bit above the second star in the uppermost row of stars is a faint misty spot that you might be able to see with your naked eye.  This is the Andromeda Galaxy, 2.5 million light years from earth, and the farthest object that you can see without binoculars or a telescope.  A light year is the distance that a photon of light travels in a year, approximately 6 trillion miles. 

The Southern Sky

Now turn the map 90 degrees so that south is at the bottom and turn yourself 90 degrees, too, so you are facing south.

Jupiter and Saturn

If you are correctly oriented, you should see two bright stars near the southern horizon.

The brightest “star” is actually the planet Jupiter and the other bright “star” at the 9 o’clock position from Jupiter is the planet Saturn.

Jupiter is the largest of the planets and takes about 12 years to orbit the sun.  Saturn, which has beautiful rings surrounding it, is the second largest planet.  Saturn takes 29 ½ years to orbit the sun.

Another way to consider the length of time it takes for these two planets to orbit the sun is to realize that Jupiter will not be in this part of the sky again until 12 years from now. Saturn will not be in this position again until around 2050.


Reorient yourself and the map back towards the east. The planet Mars rises in the east at about 8:00 p.m. below the Great Square of Pegasus.  It is a brilliant red color and cannot be missed.  To see it at its best look for it at around 9:00. It will be rising higher and higher in the evening sky in the coming weeks.


If you are an early riser you will be able to see the planet Venus in the dawn sky, blazing away in a ball of brilliant white light.

This concludes your self-guided September Night Sky Tour. When social distancing circumstances allow, we look forward to hosting these celestial events in person again. Until then, we’ll offer these astronomy opportunities and hope you enjoy the autumn season.