Autumn Stars in the Northern Hemisphere
Spring Stars in the Southern Hemisphere.
During the early autumn, as the Earth continues to orbit the Sun, the last of the summer stars such as Altair, Vego, Deneb, Nunki and Kaus Australis move away to the west. Other stars have taken their place in the northern night sky including Alpheratz of the constellation Andromeda, Sadalsuud of Aquaries and Markab of Pegasus.
In this article we will look more closely at the northern hemisphere’s autumn constellations excluding the circumpolar constellations which we have already discussed.
Andromeda. The Chained Maiden.
Andromeda is a constellation in the northern hemisphere and is visible between latitudes 90oN and 60oS. The brightest star in Andromeda is Alpheratz which is also included in the constellation Pegasus. Alpheratz is a navigational star which, for navigators, is best seen in the northern hemisphere during nautical twilight in the month of November.
The constellation Andromeda is named after Andromeda, the wife of Perseus in Greek Mythology. It is sometimes called the ‘Chained Maiden’ because according to the legend, Andromeda was rescued by Perseus who found her chained to a rock and left as a sacrifice to the monster Cetus.
How to find Andromeda. The next diagram shows that, if a line from the Pole Star to Segin in Cassiopeia is extended by about one hand-span, it will point to the star Almark of Andromeda; alternatively, a line from the Pole Star through the star Caph Beta of Cassiopeia will point to Alpharatz in Andromeda. (Note. Cassiopeia is one of the northern hemisphere’s circumpolar constellations which we discussed in part 3 of this series).
Pegasus. The Winged Horse.
As shown in the following diagram, once we have found Andromeda, we will also have found the constellation Pegasus because the star Alpheratz in Andromeda is also included in what astronomers call the ‘The Great Square of Pegasus’.
Pegasus, which is the 7th largest constellation in the sky, is in the northern hemisphere and can be seen from 90oN to 60oS. It has two navigational stars, Enif and Markab which, for navigators, are best seen during nautical twilight in the month of October.
In Greek mythology, the winged horse Pegasus is said to have leaped from the body of the Gorgon Medusa after she had been slain by Perseus. The hero Bellerophon tamed the winged horse and tried to ride it to Olympus. However, Bellerophon fell from Pegasus but the horse made it to Olympus where it was kept by Zeus to carry his thunder and lightning.
The ‘Great Square of Pegasus’ is a large asterism which is said to mark the body of the winged horse. This asterism is formed by the stars Scheat, Markab, Algenib and Alpheratz (which is also in Andromeda). The brightest star in Pegasus is Enif which is said to mark the horse’s nose.
PISCES, The Fish
Pisces is a large ‘V’ shaped constellation which straddles the equator and lies on the path of the ecliptic. It is visible between latitudes 90oN and 65oS; it is best seen in November. The brightest star in Pisces is Alpherg or Kullat Nunu but this is not a navigational star; in fact, this constellation contains no navigational stars.
The reason that we have included Pisces in this ‘route map’ is because of its association with the ‘First Point of Aries’ which is the point at which the Sun crosses the celestial equator when it is moving from south to north along the ecliptic. This event occurs on 21/22 March and is known as the vernal Equinox. The confusing thing is that, although the ‘First Point of Aries’ lay in the constellation of Aries when it was chosen by the ancient astronomers, due to precession, it now lies in Pisces.
The name Pisces is derived from the Latin for fish and is said to depict two fish, swimming in opposite directions, held together by a piece of string connecting their tails. The star Alrisha is said to be the knot that ties the strings that hold the two fish together. In ancient Greek mythology, Pisces is associated with the fish that carried Aphrodite and Eros to safety from the monster Typhon. In another mythological tale, the fish of Pisces were said to have been spawned by the ‘Great Fish’ in the constellation Pisces Austrinus which is known as the ‘Southern Fish’.
Finding Pisces. Pisces lies just to the south of the ‘Great Square of Pegasus as shown in the diagram which follows. If a line is drawn from Scheat to Algenib in Pegasus and extended by about one hand-span, it will point to the star Alrisha in Pisces; however, this constellation is very hard to find because it is so faint.
Aquarius, the Water-Bearer
In a popular song, the words the ‘the dawning of the age of Aquarius’ refer to the period when the vernal equinox will lie inside the constellation Aquarius. The vernal equinox is the point where the Sun crosses the Equator on its northward movement along the ecliptic and heralds the first day of spring in the northern hemisphere on 20th./21st. March. This point is known as the ‘First Point of Aries’ because in 150 B.C. when Ptolemy first mapped the constellations, Aries lay in that position. However, although still named the ‘first point of Aries’, due to precession, the vernal equinox now lies in the constellation Pisces, so logically, it should be named the ‘first point of Pisces’ since we are now in the ‘Age of Pisces’. There are various predictions of when the next ‘age of Aquarius’ will begin but the most prominent of these is about 2600 A.D.
Aquarius is a constellation in the southern hemisphere and is visible at latitudes between 65oN and 90oS; it is best seen during the month of October. The brightest star in Aquarius is Sadalsuud an Arabic phrase meaning “luck of lucks”. Sadalsuud is not a navigational star and in fact, there are no navigational stars in the constellation Aquarius which, like Pisces, is very faint and difficult to see with the naked eye.
In ancient Greek mythology, Zeus transformed himself into an eagle (Aquila) to carry a young man named Ganymede to serve as a cup-bearer to the gods in Olympus. The name Aquarius is derived from the Latin for ‘water-bearer’ or ‘cup-bearer’.
Finding Aquarius. Aquarius is a very faint constellation and is difficult to locate. However, this diagram shows that if we line up the two stars that form the base of the triangle at the top of the ‘Ring of Pisces’ and extend that line it will point to the star Sadalmeilk in the constellation Aquarius which is to the south of Pegasus. If we also run a line from Scheat to Markab in Pegasus and extend that line by a palm-width, that too will point to Aquarius.
Piscis Austrinus. The Great Fish or The Southern Fish
The small constellation Piscis Austrinus, also called Piscis Australis, lies in the southern hemisphere and is visible between latitudes 55oN and 90oS.
It contains mostly faint stars except for Formulhaut which is one of the brightest stars in the sky and is a navigational star. Because it’s the only bright star in this part of the sky, Fomalhaut is sometimes called the “Lonely Star of Autumn”. For navigators, the best time to see Formulhaut is during nautical twilight is in the month of October.
Piscis Austrinus is associated with the Babylonian myth about the goddess Atargatis who fell into a lake and was rescued by a large fish. The ancient Greeks named the constellation the ‘Great Fish’ which, according to Egyptian mythology, saved the goddess Isis who, as a reward, sent it into the sky where it spawned the two fish in the constellation Pisces. The name Piscis Austrinus is derived from the Latin for the ‘Southern Fish’.
Finding Piscis Austrinus Fomulhaut was once considered to be part of Aquarius as well as the constellation Pisces Austrinus, where it now belongs. Formulhaut is depicted as the toe of Aquarius and this idea provides us with a way of locating both Aquarius and Pisces Austrinus for if we can find Formulhaust, the brightest star in the region, then we can find both of those constellations. The following diagram shows Pisces Austrinus nestling at the foot of Aquarius with Formulhaut providing the link between them.
The Autumn constellations, Pegasus, Andromeda, Pisces, Aquarius and Piscis Austrinus sink into the west after December and waiting in the wings to the east are the winter constellations of Orion, Taurus, Auriga, Perseus, Gemini, Canis Major and Canis Minor; these will be the subject of the next article in this series.
Links: Stars For All Seasons – Part 1
Stars For All Seasons – Part 2
Stars For All Seasons – Part 3
Stars For All Seasons – Part 4
Books of the Astro Navigation Demystified Series:
Applying Mathematics to Astro Navigation
Astronomy for Astro Navigation
Celestial Navigation. Theory and Practice
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