INTRODUCTION TO BASIC

OBSERVATIONAL ASTRONOMY

WHETHER NAKED EYE, BINOCULARS OR USING A TELESCOPE

THE FOLLOWING BASIC KNOWLEDGE AND SKILLS ARE

REQUIRED.

1. DARK ADAPTION

ALLOW THE EYES 20 MINUTES OR MORE TO ADJUST TO DARKNESS IN

ORDER TO BECOME SENSITIVE TO FAINT LIGHT.

A DIMMED (RED CELLOPHANE) TORCH WILL PROVIDE ENOUGH LIGHT

WHEN DARK ADAPTED.

2. AVERTED VISION

LOOKING SLIGHTLY TO THE SIDE OF A FAINT OBJECT, INSTEAD

OF DIRECTLY AT IT, GIVES A MUCH IMPROVED VIEW, BECAUSE

THE RETINA IS MOST LIGHT-SENSITIVE AROUND THE

EDGES.IT IS ALSO IMPORTANT TO MOVE THE EYES AS AN IMAGE

ON THE RETINA BECOMES IGNORED BY THE BRAIN AFTER

A TIME.

3. LIMITING MAGNITUDE

THE BRIGHTNESS OF THE FAINTEST STAR THAT CAN BE SEEN

ONA GIVEN NIGHT.

A DARK ADAPTED NAKED EYE HAS AN APERTURE OF ABOUT 7MM

(THE PUPIL) SO STARS TO ABOUT MAG. 6 CAN BE SEEN.

BINOCULARS (50MM APERTURE) MAG. 10

OBSERVING FAINT OBJECTS IS A SKILL, THE EYE-BRAIN SYSTEM

BENEFITS FROM PRACTICE AND EXPERIENCE.

A SKILLED OBSERVER UNDER DARK SKIES CAN SEE AS MUCH AS

TWOMAGNITUDES FAINTER THAN A NOVICE.

MAGNITUDE LIMITS

MAG. LIMITNO. OF STARSDESCRIPTION

2.5 93IN CRUX ONLY 3

STARS SEEN

3.5 283

4.5 893N.E. FROM CITY

5.0N.E. IN AVERAGE SKIES

5.5 2822N.E. IN BEST

SEMI-DARK SKIES

6.5 8768 N.E. FROM RURAL SKIES

7.5 26533 BINOCULAR LIMIT

WITHIN CITY

10.0 BINOCULAR LIMIT IN

BEST SEMI-DARK SKIES

10.5 ~60 000 BINOCULAR LIMIT IN VERY

DARK SKIES

15CM TELESCOPE IN CITY

11.5~180 000 LIMIT OF 60MM TELESCOPE

12.5 ~540 000 15CM TELESCOPE FROM

SEMI-DARK SKIES

ANGULAR SEPARATION

DISTANCES IN THE NIGHT SKY ARE MEASURED IN DEGREES (OR FINER

DIVISIONS).

· FIST AT ARMS LENGTH 10º

· A FINGERTIP 1º

A DEGREE IS DIVIDED INTO 60 ARC MINUTES () THE SUN AND MOON

ARE EACH ½º OR 30.

ONE ARC MINUTE IS DIVIDED IN 60 ARC SECONDS ().

E.G.

JUPITERS DISC IS 40 ACROSS IF VIEWED WITH 7-POWER

BINOCULARS THE DISC APPEARS TO BE 7 X 40 = 280 RENDERING

IT VISIBLE AS IT NOW EXCEEDS THE RESOLUTION OF THE

NAKED EYE WHICH IS 60.

RESOLVING POWERS

APERTURERESOLUTION

NAKED EYE60

60MM2.3

90MM1.6

15CM (6 INCH) 0.93

20CM (8 INCH) 0.70

25CM (10 INCH) 0.56

OTHER RESOURCES

FOR BASIC OBSERVING

1. LEARN BRIGHT STARS AND CONSTELLATIONS

2. DETAILED STAR CHARTS

E.G.

· SKY ATLAS 2000 TIRION DETAILS STARS TO

MAGNITUDE 8

· 43 000 STARS

· 2 500 CLUSTER, NEBULAE, GALAXIES.

3. COMPUTER PROGRAMS

E.G.

· CYBERSKY 8403 STARS TO MAG. 6.5

· STARRY NIGHT PRO 19 MILLION STARS TO

MAG 16.5

4. ACCURATE TIME

E.G.

· NEEDED FOR TIMING LUNAR OCCULTATIONS,

CRATER TIMINGS DURING LUNAR ECLIPSE.

AREAS OF OBSERVATIONAL

ASTRONOMY

SOLAR OBSERVING

· MONITOR SUN SPOT ACTIVITY

LUNAR OBSERVING

· LUNAR FEATURES

· ECLIPSES

· LUNAR OCCULTATION (TOTAL AND GRAZING)

PLANETARY OBSERVING

· INCLUDING PHENOMENA OF GALILEAN MOONS,

ECLIPSES,TRANSITS, OCCULTATIONS

· MINOR PLANETS (ASTEROIDS)

COMETS

· METEOR SHOWERS

STARS

· DOUBLE STARS

· VARIABLE STARS (OVER 30 000 KNOWN, HOWEVER,

LESS THAN400 ARE PRESENTLY BEING OBSERVED FROM

SOUTHERN AFRICA).

DEEP SKY

· GALAXIES

· STAR CLUSTERS

· NEBULAE (BRIGHT, REFLECTION, PLANETARY)

· DARK NEBULAE

· GLOBULAR CLUSTERS

OTHER INTERESTING AREAS

· ASTROPHOTOGRAPHY

· TRACKING ARTIFICIAL SATELLITES, EG. ISS, HST

INCLUDING IRIDIUM COMMUNICATION SATELLITES THAT CAN PRODUCE

SPECTACULAR FLARES (MAG. 8) WHEN THE SUN GLINTS OFF THEIR

SHINY SURFACES.

Abas, the son of Lynkeus and Hypermestra, followed the family tradition and had twin sons, Proitos and Akrisios. The twins fought continually, even while still within their mother's body, and continued their conflict as they grew up. Eventually Proitos left and started a new kingdom at Tiryns, only a few miles south of Argos, while Akrisios assumed the kingship of Argos. He married a woman (whom late sources name Eurydike) and had a daughter Danae. He then inquired of the Delfic oracle as to how he could have a son. This is the basic pattern of most Greek heroic myth. When a king's wife either has no children or produces a daughter, the king asks an oracle about having a son. The answer is almost always the same: don't have a son, or that son will kill you. If the king has a daughter, he is told by the oracle not to let his daughter get married. If she does, the king will be killed by some version of a son (e.g., grandson, son-in-law, stepson). So all these kings with daughters proceed to impose an apparently impossible task upon any suitors of their daughters. To become a hero, therefore, you had to overcome an insurmountable obstacle (which always means to win a princess from her father by doing something impossible for everyone else). For example, if a suitor wished to marry Hippodameia, daughter of king Oinomaos of Olympia, he had to beat her father in a chariot race (but Oinomaos had the fastest horses in the world, and the suitor had to take Hippodameia with him in his chariot). If he wanted to marry Iole, daughter of king Eurytos of Oichalia, he had to beat her father in an archery contest (and Eurytos was the best archer in the world). And if he wanted to marry Alkestis, daughter of Pelias, he would have to yoke a lion and a boar to a plow (something only Pelias could do). In the case of Akrisios and his daughter Danae, he was told by the oracle that if his daughter married, she would have a son who would kill him. Akrisios therefore locked up Danae in a bronze underground dungeon, and set guards to watch over the prison. One day, however, Akrisios came to visit his daughter and discovered that Danae had a baby named Perseus. Who was the father? Some said it was Zeus, who came through the keyhole in the form of golden rain, and others said it was Akrisios' twin brother Proitos, Danae's uncle, who had bribed the guards with gold and then made up the story of Zeus and the golden shower. Danaos took his daughter and her baby son a few miles south to Nauplion, put them in a box, and threw the box into the Aegean Sea. This is another recurrent aspect of heroic myth: the infant hero-to-be is almost always exposed by his father (or sometimes mother) to what seems to be certain death in the sea or the wilderness. These children sent to die always survive, of course; usually they are found and raised by parents of low status (or sometimes even by animals) and they eventually seek out their true parents. The oracle is always fulfilled (that is, the king dies), the mother is often rescued from some terrible predicament, and it is often in the quest for his real parents that the heroic status of the son is attained. The box containing Danae and Perseus washed ashore on the island of Serifos and was found by a poor fisherman named Diktys. He had once been the king of Serifos but he was deposed by his twin brother Polydektes. When Diktys found and opened the box, he immediately fell in love with Danaeand told her, "I love you and would marry you if I could, but you are obviously a princess and I am a poor fisherman. Still I will protect you from all other men, and I will raise your son Perseus as if he were my own." When Perseus was 21 years old, king Polydektes saw Danae and fell in love with her. Since he could tell that Perseus was a son of Zeus, he had to figure out some way to get rid of him. Making up a false story, he announced that he intended to court Hippodameia, daughter of king Oinomaos of Olympia. Since he didn't want to engage in the chariot race with Oinomaos, which all other suitors had lost, along with their heads,he told his people that he had a different strategy. If all his subjects gave him a horse, he would take the entire herd to Oinomaos, who might then be so grateful that he would hand over his daughter without forcing Polydektes to race. All of Polydektes' subjects brought him a horse; finally it was Perseus' turn, and he told the king, "I live with the poor fisherman Diktys and we have no horses. But I am a loyal suject and I would do anything for you, even bring back the head of the Gorgon Medousa." This is just what Polydektes wanted to hear, and he commanded Perseus to bring him Medousa's head, figuring that such a task would cause the certain death of Danae's son. The three Gorgons were Medousa, who was mortal, and her immortal sisters Sthenno and Euryale. They lived in what is now called Morocco, near the paradise Garden of the Hesperides (one of the several Greek versions of the Garden of Eden). They had tusks like a boar, wings, snakes instead of hair, and the power of turning to stone anyone whose eyes met theirs (that is, if a Gorgon saw you looking at her you would be petrified and die). Perseus, however, had no idea where the Gorgons lived and was wandering around Serifos helplessly until Athena came to his aid. Athena, the goddess whose entire career is dedicated to disguising herself as a man, is the great friend and helper of most heroes, just as Hera is usually their greatest enemy (since most heroes are the illegitimate sons of her husband Zeus). When Perseus asked Athena where the Gorgons lived, she told him that there were three nymphs who knew the answer. Perseus said, "What three nymphs? There's a nymph for every pond and fountain, a nymph for every tree, and hundreds more in the ocean." Athena replied that the three Graiai knew which three nymphs knew the home of the Gorgons. The three Graiai were old hags who had been born as old hags. They had one eye and one tooth between the three of them, and both were detachable. If a Graia wanted to eat something, she said, "Pass the tooth," and if she wanted to see what she was eating, she said, "Pass the eye." Perseus found the Graiai, snatched away the eye and tooth as they were passed around, and refused to give them back until they revealed the identity of the nymphs. Then he went to the nymphs, learned where the Gorgons lived, and received from the nymphs and from Athena many gifts to help him get the head of Medousa. He received a shield with a mirrored surface (so he could see the Gorgons indirectly), a special bag kalled the kibisis (to put Medousa's head in, so he wouldn't accidentally look at it), a sickle to cut off her head, winged sandals (so he could fly), and the cap of Hades (which made whoever wore it invisible). Weighted down with all these implements, Perseus flew to the Garden of the Hesperides, where he found the three Gorgons asleep on the ground. Looking in the mirror-shield, and with Athena guiding his hand, he cut off Medousa's head. As soon as he did this, the winged horse Pegasos and an armed warrior named Chrysaor jumped out of the neck of headless Medousa. She had recently had an affair with Poseidon, and had become pregnant with these two children. The noise of this double birth awakened her sisters and they started to pursue Perseus. Putting on the cap of Hades, however, he became invisible to them and easily escaped. Perseus then began his return to Serifos, where his mother Danae was being pursued by the lecherous Polydektes (who was sure that Perseus would never return). As Perseus flew over Ethiopia (probably modern Haifa) he looked down and saw what was apparently a princess about to be eaten by a huge sea serpent. He flew to the palace of the king, Kepheus, and asked what was happening. Kepheus told Perseus that because of the arrogance of his wife Kassiopeia Poseidon had sent the sea serpent to harass his country. When he asked the oracle how he could get rid of the monster, he was told the only way was to sacrifice his most precious possession, his daughter Andromeda. Perseus asked, "If I kill the sea serpent and rescue Andromeda, can I marry her?" When the king agreed, Perseus flew to the coast, took Medousa's head out of the kibisis and showed it to the monster, who was turned to stone. He then returned with Andromeda to the palace, where king Kepheus told him, "There's one thing I forgot to tell you. To marry Andromeda you first must defeat her fiancee, my twin brother Phineus, and his army." Perseus again used Medousa's head to turn Phineus and his army to stone, then flew back to Serifos to rescue his mother. After finding Danae and her protector Diktys, who had taken refuge on an altar, he turned Polydektes and his entire army to stone. He then restored Diktys to his rightful position as king of Serifos and announced his intention of returning to Argos to visit his grandfather Akrisios. At this point we would certainly expect Danae and Diktys to get married and live happily ever after; he had loved and protected her for all these years, but could not marry her because of his poverty. But even though he now is king again, Danae cannot be allowed to marry. Perseus flew back to Argos with his bride under one arm and his mother under the other. When a man takes his mother on his honeymoon, we might well wonder whom he is really marrying. But of course Andromeda and Danae are two aspects of the same person. That is why they first appear in exactly similar situations. When he arrived in Argos, he discovered that Akrisios had disappeared and no one knew where he was (when Akrisios learned that Perseus, the grandson who was destined to kill him, was going around turning people to stone, he had left Argos and was secretly living in the northern Greek city of Larissa under an assumed name). Perseus therefore assumed the kingship of Argos, and he and his wife Andromeda had many children. Some years later Perseus went up to Larissa to participate in athletic games being held in honor of a dead king. Since Perseus had recently invented discus-throwing, the people of Larissa invited him to demonstrate this new sport. Perseus threw the discus very far and rather wildly; it sailed into the stands, struck Akrisios on the foot, and killed him instantly. When he returned to Argos, Perseus was ashamed to be king of the city whose former king he had just killed. He therefore arranged an exchange with his father's twin brother Proitos, king of Tiryns. Proitos and his son Megapenthes came to rule Argos, while Perseus became king of Tiryns. At this time Perseus founded the city of Mycenae.