Cepheus Constellation

King Cepheus of Aethiopia is a constellation very near to the north star that will become home to the polar north in the coming millenia. The constellation is overshadowed by nearby Cassiopeia with much brighter stars. The constellation is visible year around in the northern hemisphere and is such considered a circumpolar constellation as it appears to rotate around the north star. Cepheus is linked to many other constellations through Greek mythology. His wife was Queen Cassiopeia, his daughter was Andromeda, his son in law was Perseus.

Cepheus constellation is one of the original 48 constellations listed by the Egyptian mathematician Ptolemy, who lived under Roman rule in Alexandria in the 2nd century. These constellations formed the basis for the modern list agreed by the IAU. Constellations from the southern hemisphere, unable to be seen from the Mediterranean, represent the majority of additions to the list.

As the earth moves in its orbit around the sun, each night you are looking at a different portion of the sky. When looking at stars it is important to be aware of what is within your view. Northern hemisphere stargazers can group constellations into 3 groups; circumpolar, summer and winter constellations. The circumpolar constellations are in the north sky, appear to move around the north star and are visible throughout the year. The constellations in the south sky are only visible for part of the year and are grouped as either summer or winter constellations. Each is visible from between 4 to 10 months.

It is important to be aware of the specific time of year and hour of the night when deciding what to look for. These pages below show the constellations in each group so you can find the constellations that interest you.

CIRCUMPOLAR (year around) – Ursa Major – Cassiopeia – Ursa Minor – Draco – Cepheus

WINTER – Pegasus – Pisces – Aries – Auriga – Taurus – Orion – Canis Major  – Canis Minor – Gemini – Lynx – Cancer – Leo – Winter Hexagon

SUMMER – Virgo – Libra – Scorpius – Bootes – Hercules – Lyra – Ophiuchus – Sagittarius – Aquila – Cygnus – Capricornus – Aquarius

Or use this guide to easily see which constellations are easiest to find right now:

BEST CONSTELLATIONS TO FIND THIS MONTH

Cepheus Quick Facts:

Symbolism: King Cepheus

Neighbouring constellations: Ursa Minor*, Cassiopeia*, Cygnus*, Draco*, Pegasus* 

Brightest star: Alderamin, 2.45 magnitude (89rd brightest star in night sky)

Stars brighter than 3 magnitude: 1

Primary stars: 5 (polygon in house form with 4 points of a square and a point above at the peak of the roof)

Latitude: 60 – 80 degrees north

Northern Hemisphere Season: Circumpolar (year round)

*Circumpolar constellations do not maintain the same coordinal direction to each other as they all rotate around the north star Polaris in the constellation Ursa Minor. The direction however can always be determined from the constellation with the top of the W pointing to the north star.

Which months can you see Cepheus constellation?

Cepheus can be seen all year but can be found high in the sky at 21:00 from September to November:

• Early evening viewers (pre 21:00) can find the constellation from June in the north east sky until February in the north west sky. Cepheus will be visible overhead from October to December.
• Mid evening viewers (21:00-23:30) can find the constellation from May in the north east sky until January in the northwest sky. Cepheus will be visible overhead in from August to October. 
• Late evening viewers (after 23:30) can find the constellation from April in the north east sky until November in the north west sky. Cepheus will be visible overhead from June to September.
• Early morning viewers can find the constellation from January in the north east sky to September in the north west sky. Cepheus will be visible overhead from from April to July.

As time passes the constellation will gradually appear earlier in the day with ranges below showing the window of opportunity in each month. Cepheus sits between 60-80 degrees north latitude. Therefore, the further south your position the lower it will appear in the north sky. At its maximum range it is possible to see Cepheus at latitudes between +90 and -10. Above Latitudes of 30 degrees north the constellation remains above the horizon at all times.

Best time to see Cepheus:

Present throughout night from June to October

Best visible at 21:00 from September to November

January: visible in the north west sky at sunset 40 degrees above horizon. It will rotate towards the horizon, dropping too low in the sky to observe after 21:30. It will return to 15 degrees above the north east horizon at 05:00, increasing to 20 degrees by sunrise.

February: visible in the north west sky at sunset 25 degrees above horizon. It will rotate towards the horizon, dropping too low in the sky to observe after 20:00. It will return to 15 degrees above the north east horizon at 03:00, increasing to 30 degrees by sunrise.

March: in the evening sky the constellation will be very low on the horizon and difficult to observe. It will return to 15 degrees above the north east horizon at 01:00, increasing to 40 degrees by sunrise.

April: in the evening sky the constellation will be very low on the horizon and difficult to observe. It will return to 15 degrees above the north east horizon at 24:00, increasing to 50 degrees by sunrise.

May: in the evening sky the constellation will be very low on the horizon and difficult to observe. It will return to 15 degrees above the north east horizon at 22:00, increasing to 55 degrees by sunrise.

June: visible throughout the night appearing in the north east sky at sunset 20 degrees above horizon. It will reach its peak 60 degrees above the north horizon at 04:30, and lower slightly to 55 degrees by sunrise.

July: visible throughout the night appearing in the north east sky at sunset 30 degrees above horizon. It will reach its peak 60 degrees above the north horizon at 02:30, and lower to 50 degrees by sunrise.

August: visible throughout the night appearing in the north east sky at sunset 40 degrees above horizon. It will reach its peak 60 degrees above the north horizon at 24:30, and lower to 35 degrees in the north west sky by sunrise.

September: visible throughout the night appearing in the north east sky at sunset 50 degrees above horizon. It will reach its peak 60 degrees above the north horizon at 22:30, and lower to 20 degrees in the north west sky by sunrise.

October: visible throughout the night appearing in the north sky at sunset 55 degrees above horizon. It will reach its peak 60 degrees above the north horizon at 21:00, and becomes only partially visible from 04:30 in the north west sky.

November: visible in the north sky at sunset 60 degrees above horizon. It will rotate towards the horizon through the north west sky and become only partially visible from 01:30.

December: visible in the north west sky at sunset 50 degrees above the horizon. It will rotate towards the horizon through the north west sky and become only partially visible from 23:30.

Trajectory: The constellation is between 60-80 degrees north, placing it around 20 degrees from Polaris. The constellation will rotate around the northern star maintaining its distance. As such viewers can expect it to follow an arch from the north east horizon arching across the north east sky until it reaches its peak high in the north sky, then following a parallel arch in the north west sky until it reaches near to the north west horizon. Those at very high northern hemisphere latitudes may also be able to view it cross low in the north sky to complete its rotation. Its peak trajectory in Wadi Rum is 60 degrees above the northern horizon and is viewable in the evening from July to December.

Not the right time for Cepheus? Have a look what constellations you can see tonight.

How to find Cepheus constellation?

Difficulty to find: Medium – Difficulty to interpret: Hard – Locating asterism: Cassiopeia

Cepheus constellation itself is not easy to locate as it has only prominent star. It is however made easier because it neighbours the constellation of Cassiopeia which is one of the easiest constellations to find without aides in the northern hemisphere sky. Cepheus is in the portion of the sky between Cassiopeia and Ursa Minor which is home to the north star.

Step 1: Make sure you are familiar with what time of night the constellation will be in the sky for the time of year you are looking. Use the guide above to confirm the cycles and the appropriate area of the sky

Step 2: The constellation will always be in the north sky so orient yourself with a clear view of the sky to the north.

Step 3: Identify the prominent W shape of the Cassiopeia constellation. First follow the instructions on how to find Cassiopeia if required. 

NOTE: All 5 stars in Cassiopeia are very bright between 2 and 3.5 magnitude so should be prominent in the sky.

Step 4: the two stars at the end of the W point towards Alderamin which is the brightest star in the Cepheus constellation. Follow the direction formed by these 2 stars moving up from the W. Alderamin is 5 times the distance between these stars away and is the brightest star in this section of the sky.

Learn how to form the shape of Cepheus constellation

Now that you have found the Cepheus constellation you can use Alderamin as a reference to form the shape of the constellation. The shape of Cepheus is a simple polygon. It is similar to a simple 2D childrens drawing of  house (a triangle on top of a square). It has several minor stars that do not aide in recognising its form so for most amateur stargazers the 5 brightest stars in this shape are the focus.

For the following explanation we will use this house shape to describe the locations of the primary stars. To get an idea of the direction of the constellation the point at the roof of the house is pointing between Cassiopeia and Ursa Minor towards the nose of Ursa Major.

• Alderamin is the bottom right corner
• From there moving back towards the line from Cassiopeia you used to identify Alderamin, move 45 degrees further to the left and around double the distance between the stars in Cassiopeia to find the other star at the base of the house.
• From this point turn 90 degrees right and a slightly further distance away you will find the top left corner of the house.
• From Alderamin moving in a parallel line to the other wall of the house and a similar distance you will find the top right corner of the house.
• Finally the peak of the roof can be found at around 30 degree angles from the corners and almost twice the width of the house away. It is a higher roof than the typical children’s depiction.

Now you have found the primary 5 stars of Cepheus the most challenging part of trying to imagine the shape of a king from this formation. The king appears inverse to the house. So his feet are at the top of the roof and the base of the house is his shoulders. There are also some other dim stars near the shoulders that represent his arms but they are difficult to differentiate. It is rare for someone to be convinced of a shape that reflects a king but try your best to use this primary shape as a basis.

King Cepheus in the Ancient World

Greek mythology

Cepheus was the king of Aethiopia, which was a historic region of the upper Nile and where modern day Ethiopia derives its name. He shared the throne with Queen Cassiopeia and now share neighbouring constellations in the night sky.

King Cepheus is best is known from Greek mythology from the story of Perseus. His wife Cassiopeia made claim that their daughter Andromeda was as beautiful as Poseidon’s sea nymphs. Poseidon was angered by this and sent Cetus a sea serpent to kill Andromeda. Cetus destroyed everything in his path as he searched the lands for Andromeda. It was told that the only way to stop Cetus was to sacrifice Andromeda so she was chained naked to a rock. Perseus came to the rescue of Andromeda, killing Cetus and setting her free.

Perseus then decided to wed Andromeda despite her previously agreeing to a marriage with Phineus. At the wedding a conflict broke out and Perseus turned Phineus to stone with the head of Medusa which he had cut off in an earlier quest. 

Main stars of Cepheus constellation

Alderamin (+2.45, 49ly, 10 suns, #89)

Alderamin is from Arabic meaning ‘right arm’ due to its position in the queens chest. It is the 89th brightest star with an apparent magnitude of +2.45. The distance from earth is 49 light years. It is 10 times the size of the sun. Alderamin is the star at the right base of the house but is intended to represent the shoulder of Cepheus.

Errai (+3.21, 45ly, double star, #212)

Errai is from the Arabic meaning ‘shepherd’. It is the 212th brightest star with an apparent magnitude of +3.21. The distance from earth is 45 light years. It is a double star system. Errai will replace Polaris as the north star in around 1000 years. Errai is the star at the peak of the roof of the house but is intended to represent the feet of Cepheus.

Alfirk (+3.23m, 690ly, triple star, #216)

Alfirk is from Arabic meaning ‘the flock’ (of sheep) and in was part of an ancient Arabic asterism of the flock along with Alderamin and Alkidr. It is the 216th brightest star with an apparent magnitude of +3.23. The distance from earth is 690 light years. It is a triple star system with two stars orbiting each other and the third orbiting the 2 primary stars. Alfirk is the star at the top right corner of the house but is intended to represent the waist of Cepheus.

Zeta Cephei (+3.39m, 840ly, 830k suns. #256)

Zeta Cephei does not have an official name and instead is named by its constellation and associated Greek letter as all stars have been attributed for scientific differentiation. It is the 256th brightest star with an apparent magnitude of +3.39. The distance from earth is 840 light years. It is 830 times the size of the sun. Zeta Ceph marks the star at the left base of the house but is intended to represent the shoulder of Cepheus

Iota Cephei  (+3.50m, 206ly, 1k suns, #288)

Iota Cephei does not have an official name and instead is named by its constellation and associated Greek letter as all stars have been attributed for scientific differentiation. It is the 288th brightest star with an apparent magnitude of +3.50. The distance from earth is 206 light years. It is 13300 times the size of the sun. Iota Cephei marks the star at the top left corner of the house but is intended to represent the waist of Cepheus.

Wadi Rum is one of the best locations in the world to see the full beauty of the stars. Combining high altitudes, clear skies and no light pollution. You may be surprised how many stars are visible to the naked eye. Come with us and spend a night under the stars.