Destination Constellation : Capricornus
Join us in this edition of “Destination Constellation” as we take a closer look at Capricornus. Its the “Sea Goat”and is one of the signs of the Zodiac, part of the original 48 constellations. Listed by Ptolemy it is one of the modern 88 constellations. It is most commonly referred to as Capricorn and it contains 13 primary stars and 49 Bayer/Flamsteed designated stars. It is positioned on the ecliptic plane and bordered by the constellations of Aquarius, Aquila, Sagittarius, Microscopium and Piscis Austrinus.
In mythology, Capricornus may very well be one of the oldest constellations known. Despite being somewhat dim, it falls in an area of the sky known as the sea, it became considered a sea-goat (in the same sense as a sea-maiden). Depictions of a goat or goat-fish have been found on Babylonian tablets dating back three thousand years. The constellation may owe its antiquity to the fact that at that time, the northern hemisphere’s Winter Solstice occurred while the sun was in Capricorn. The concern for the sun’s rebirth might have rendered astronomical and astrological observation of this region of space very important.
For the same reason, the sun’s most southerly position, which is attained at the northern hemisphere’s winter solstice, is now called the Tropic of Capricorn, a term which also applies to the line on earth where the sun is directly overhead at noon on that solstice.
The poor presence of stars near this constellation with respect to Sagittarius which has instead the brightest part of the milky way, was given a mythological explanation in ancient Greece: Due to early Greek beliefs that sin accumulated throughout the year, causing the darkness to increase, together with the sun’s descent and pause at the Solstice, the ancient Greeks referred to this area of sky as the Augean Stable, where they considered the sun stabled during the year. The cause of the association with the location or name of Augeas is not currently known. Perhaps an association could be made with the Labours of Hercules (or Heracles) who had to clean out the Augean Stables which had never been cleaned out before. The gradually accumulated dung could be synonymous with the gradually accumulated sins. However, during the classical period of Greek history, this name gradually fell out of use.Due to the precession of the equinoxes, the December solstice no longer takes place while the sun is in Capricorn, but the astrological period called Capricorn begins at approximately the same time as the solstice.
About The Goat
This constellation is sometimes identified as Amalthea, the goat that fed the infant Zeus after his mother Rhea saved him from being devoured by his father Cronos in Greek mythology. The goat’s broken horn was transformed into the cornucopia or horn of plenty. Some ancient sources claim that this derives from the sun “taking nourishment” while in the constellation, in preparation for its climb back northward. However, the constellation is often depicted as a sea-goat, a goat with a fish’s tail. One myth that deals with this says that when the goat-god Pan was attacked by the monster Typhon, he dived into the Nile; the parts above the water remained a goat, but those under the water transformed into a fish. In Summer, the constellation was associated with the god Enki (Babylonian Ea), who brought culture out of the sea to humankind. The Greeks regarded the constellation area with an alternative interpretation, namely the Augean Stable – a stable full uncleanliness – representing the concept of sin accumulated during the year. The Aquarius constellation, who was said to have poured out a river, then represent the yearly cleaning rains, associating to one of The Twelve Labours of Hercules. The constellation is located in an area of sky called the Sea or Water, consisting of many watery constellations such as Aquarius, Pisces, and Eridanus.
For binocular observers, head off to to the north western corner first for Alpha Capricorni. This is an absolutely beautiful optical double star that goes by the traditional name of Algiedi. The more western of the pair is A¹ Capricorni, or Prima Giedi. Put a telescope on it, because Prima Giedi is a true binary star. Located 690 light years from Earth, Alpha¹ Capricorni A, is a yellow G-type supergiant with an apparent magnitude of +4.30. Its companion, Alpha¹ Capricorni B, is an eighth magnitude star, separated by 0.65 arcseconds from the primary. Now go back and look at Alpha² Capricorni. Its name is Secunda Giedi. Alpha² Capricorni is a yellow G-type giant with an apparent magnitude of +3.58. It is approximately 109 light years from Earth. And they looked so close when they were together!
For even more fun, aim your telescope all the way across the constellation at the northeastern corner for Delta Capricorni. Now you’re in for a real treat because Deneb Algedi is a a quaternary star system. Located 39 light years away, Delta Capricorni A, is classified a white giant star of the spectral type “A”. The system is a spectroscopic binary whose two components are of magnitude +3.2 and +5.2, and separated by 0.0018 arc seconds. Similar to Algol, Delta Capricorni A is an eclipsing binary. Its unresolved companion orbits with Capricorni A around their common centre of mass every 1.022768 days, causing the brightness to drop 0.2 magnitudes during eclipses. Two other stars are thought to orbit further out in the system. The sixteenth magnitude Delta Capricorni C is one arc minute away, while the thirteenth magnitude Delta Capricorni D is two arc minutes away from the primary.
Take A Bino Sweep
Now go back to binoculars and hop one bright star west to take a look at Gamma Capricorni. Nashira, or “the bearer of good news” is one of those really cool stars right on the ecliptic that’s often occulted by the Moon. Gamma Capricorni is also a blue-white A-type (A7III) giant star with a mean apparent magnitude of +3.69. It is approximately 139 light years from Earth. It is classified as an Alpha2 Canum Venaticorum type variable star and its brightness varies by 0.03 magnitudes. Now, go right in the center for Theta. It’s name is Dorsum – the Latin word for “Back”. Theta Capricorni is a white A-type main sequence dwarf with an apparent magnitude of +4.08. It is approximately 158 light years from our solar system. More? Then go back west with binoculars and look at Beta. Its traditional name Dabih, which comes from the Arabic, meaning “butchers”.
The Beta Capricorni system is located 328 light years from Earth and it’s a superb binary star! The brighter of these two components, Beta¹ Capricorni or Dabih Major, has an apparent magnitude of +3.05, while the dimmer one, Beta² Capricorni or Dabih Minor, has an apparent magnitude of +6.09. The two components are separated by 3.5 arc minutes on the sky, putting them at least 21,000 AU (0.34 light years) apart. They take approximately 700,000 years to complete one orbit. Both of these components are themselves made up of multiple stars.
Now, keep your binoculars handy and use the chart to help you located Messier 30. This decent globular cluster was discovered by Charles Messier in 1764 and is located about 26,000 light-years away from Earth. No wonder it’s so hard to see in binoculars! Now put your telescope on it to do some resolving…. Its brightest red giant stars are about of apparent visual magnitude 12.1, its horizontal branch giants at magnitude 15.1.
Only about 12 variable stars have been found in this globular cluster. The core of M30 exhibits an extremely dense stellar population, and has undergone a core collapse. Despite its compressed core, close encounters of the member stars of globular cluster M30 seem to have occurred comparatively rare, as it appears to contain only few X-ray binary stars.
For more advanced telescope observing, try the NGC 7103 galaxy group (RA 21 39 51 Dec -22 28 24). Averaging about 15th magnitude elliptical is extremely faint and a definite big scope challenge. It pairs with NGC 7104, which is also 15th magnitude and has no classification.
More realistically, try NGC 6907 (RA 20 25 1 Dec -24 49). At slightly fainter than magnitude 11, this classy spiral galaxy shows some nice arm structure to even mid-sized telescopes. Why? Because it is doing a little galaxy interaction with background lenticular galaxy NGC 6908. This pair of spirals is engaging in some galaxy cannibalism! This act has caused some nice supernovae events within recent history and makes for some great observing – as well as astro-imaging opportunities!
The constellation of Capricornus also has a meteor shower associated with it. The Capricornid meteor stream peaks on or about July 30 and is active about a week before and after that date. The average fall rate is about 10 to 30 per hour and it is know to produce bolides.
Written by Tammy Plotner of Universe Today.