M45 - 13 years later (2008 Dec 09)

[pcstarship]

Today's APOD post sparked a recollection for me. Back on June 20, 1995, the second-ever APOD post was an image of the Seven Sisters:

http://antwrp.gsfc.nasa.gov/apod/ap950620.html

A comparison with today's image...

http://antwrp.gsfc.nasa.gov/apod/ap081209.html

...provides an instructional demonstration of how far astronomical imagery has come in just the past 13 years.

Remarkable.

[bystander]

APOD Search: "M45" - 23 items
http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... search?M45

APOD Search: "Pleiades" - 63 items
http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... h?Pleiades

APOD Search: "Seven Sisters" - 16 items
http://antwrp.gsfc.nasa.gov/cgi-bin/apo ... en+Sisters

Asterisk Search: "M45" - 7 topics
http://asterisk.apod.com/sea ... mit=Search

Asterisk Search: "Pleiades" - 25 topics
http://asterisk.apod.com/sea ... mit=Search

Asterisk Search: "Seven Sisters" - 4 topics
http://asterisk.apod.com/sea ... mit=Search

[neufer]

PeLEIADES: `flock of doves'
http://www.naic.edu/~gibson/pleiades/pleiades_myth.html

<<One day the great hunter Orion saw the Pleiads as they walked through the Boeotian countryside, and fancied them. He pursued them for seven years, until Zeus answered their prayers for delivery and transformed them into birds (doves or pidgeons), placing them among the stars. Later on, when Orion was killed (many conflicting stories as to how), he was placed in the heavens behind the Pleiades, immortalizing the chase.

The `lost Pleiad' legend came about to explain why only six are easily visible to the unaided eye. This sister is variously said to be Electra, who veiled her face at the burning of Troy, appearing to mortals afterwards only as a comet; or Merope, who was shamed for marrying a mortal; or Celæno, who was struck by a thunderbolt. Missing Pleiad myths also appear in other cultures, prompting Burnham to speculate stellar variability (Pleione?) as a physical basis. It is difficult to know if the modern naming pays attention to any of this. Celæno is the faintest at present, but the "star" Asterope is actually two stars, each of which is fainter than Celæno if considered separately. >>
------------------------------------------------
Why can I only see six of the ``Seven Sisters''?
http://www.naic.edu/~gibson/pleiades/pleiades_see.html

<<Two major reasons:
1) the number of stars isn't really seven (it's many more), and
2) they all have different brightnesses, so that you see more or fewer of them depending on viewing conditions.

The list below is in order of decreasing brightness. Note that there are nine different starnames, but two (Atlas & Pleione) are the parents.>>

Code: Select all

        Name          Designation   Visual Magnitude
....................................................					
        Alcyone         25 Tau       2.90
        Atlas           27 Tau       3.62
        Electra         17 Tau       3.70
....................................................	
        Maia            20 Tau       3.87
        Merope          23 Tau       4.18
        Taygeta         19 Tau       4.30
....................................................	
        Pleione         28 Tau       5.09
        --             HD 23985      5.23
        Asterope 1+2   21+22 Tau     5.31 (combined)
        --             HD 23753      5.44
        Celæno          16 Tau       5.46
....................................................
        --              18 Tau       5.64
        Asterope 1      21 Tau       5.80 (separate)
        --              33 Tau       6.05
        --             HD 23950      6.07
        --             HD 23923      6.17
        --             HD 24802      6.19
        --              24 Tau       6.29
        --             HD 24368      6.34
        Asterope 2      22 Tau       6.43 (separate)
        --              26 Tau       6.47
        --             HD 23712      6.49

______________________________
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http://www.naic.edu/~gibson/pleiades/pleiades_myth.html

<<The Pleiad(e)s were the seven daughters of Atlas and Pleione, and half-sisters of the Hyades, whose mother was Æthra (`bright sky'; a different Æthra than the mother of Theseus). They were perhaps also half-sisters of the Hesperides, who were daughters of either Night alone, or Atlas and Hesperis (`evening'), or Ceto and Phorcys. Both Pleione and Æthra were Oceanids, daughters of Oceanus and Tethys, the titans who ruled the outer seas before being replaced by Poseidon. Atlas (`he who dares' or `suffers'; from the Indo-European tel-, tla-, `to lift, support, bear'), another titan, led their war against the gods, and was afterward condemned by Zeus to hold up the heavens on his shoulders. The Pleiades were also nymphs in the train of Artemis, and together with the seven Hyades (`rainmakers' or `piglets'; individual Hyad names are not fully agreed upon) were called the Atlantides, Dodonides, or Nysiades, nursemaids and teachers to the infant Bacchus. The Hesperides (`nymphs of the west'), apparently not counted in this, were only three, and dwelled in an orchard of Hera's, from which Heracles fetched golden apples in his eleventh labor.>>
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<<* Alcyone or Halcyone - `queen who wards off evil [storms]' -

Seduced by Poseidon and gave birth to either Hyrieus or Anthas, founder of Anthæa, Hyperea, and Halicarnassus.

Another Alcyone, daughter of Æolus (guardian of the winds) and Ægiale, married Ceyx of Trachis; the two jokingly called each other Hera and Zeus, vexing those gods, who drowned Ceyx in a storm at sea; Alcyone threw herself into the sea at the news, and was transformed into a halcyon (kingfisher). Legend has it the halcyon hen buries her dead mate in the winter before laying her eggs in a compact nest and setting it adrift on the sea; Æolus forbids the nest to be disturbed, so the water is calm for 14 days centered on the winter solstice, called the Halcyon Days. The actual bird does not build nests however; instead the story probably derives from an old pagan observance of the turning season, with the moon-goddess conveying a dead symbolic king of the old year to his resting place. Though this Alcyone and the Pleiad Alcyone appear to be separate individuals, they may be related: in 2000 BC, a vigorous period of ancient astronomy, the Pleiades rose nearly four hours earlier than they do today for the same time of year, and were overhead at nightfall on the winter solstice, when the Halcyon supposedly nested; their conjunction with the sun during spring equinoxes at that time may have something to do with the association of the cluster with birds, which are often used as symbols of life and renewal.>>
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<<* Electra or Eleckra - `amber', `shining', `bright' (Indo-European wleik-, `to flow, run', as a liquid); electrum is an alloy of silver and gold, and means amber in Latin, as does the Greek elektron; Thales of Miletus noted in 600 BC that a rubbed piece of amber will attract bits of straw, a manifestation of the effects of static electricity (outer charge stripping via friction), and perhaps the origin of the modern term -

Wife of Corythus; seduced by Zeus and gave birth to Dardanus, founder of Troy, ancestor of Priam and his house. Called Atlantis by Ovid, personifying the family. May also, by Thaumas, be the mother of the Harpies, foul bird-women who lived in a Cretan cave and harried criminals, but this could be a different ocean-nymph of the same name.

Another Electra was a daughter of Oedipus, though this may not be the same Oedipus who killed his father and married his mother. She is said to be mother of Dardanus and Iason.

Yet another Electra was a daughter of Agamemnon and Clytæmnestra, with an alternate name of Laodice, and with brother Orestes and sisters Chrysothemis and Iphigeneia (or Iphianassa), though the latter sister may have been Clytæmnestra's niece, adopted from Theseus and Helen. Agamemnon was king of Mycenæ and led the Greeks against Troy; he was murdered at his return by Clytæmnestra and her lover Ægisthus, both of whom Orestes and Electra killed in revenge, whence the psychological term `Electra complex'. This Electra was also wife to the peasant Pylades, and bore him Medon and Strophius the Second.>>
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<<* Maia - `grandmother', `mother', `nurse'; `the great one' (Latin) -

Eldest and most beautiful of the sisters; a mountain nymph in Arcadia. Seduced by Zeus and gave birth to Hermes. Later became foster-mother to Arcas, son of Zeus and Callisto, during the period while Callisto was a bear, and before she and Arcas were placed in the heavens by Zeus (she as Ursa Major, he as either Boötes or Ursa Minor).

Another Maia was the Roman goddess of spring, daughter of Faunus and wife of Vulcan (his Greek counterpart, Hephæstus, married Aphrodite instead). Farmers were cautioned not to sow grain before the time of her setting, or conjunction with the sun. The month of May is named after her, and is coincidentally(?) the month in which the solar conjunction happens. By our modern calendar, the conjunction occurred in April in early Roman times, with the shift since then due to the precession of the Earth's axis; but calendars too have changed over time, especially before the time of Julius Caesar, so the month and the cluster's solar conjunction may have lined up then as well.>>
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<<* Merope - `eloquent', `bee-eater', `mortal' -

Married Sisyphus (se-sophos, `very wise'), son of Æolus, grandson of Deucalion (the Greek Noah), and great-grandson of Prometheus. She bore Sisyphus sons Glaucus, Ornytion, and Sinon; she is sometimes also said to be mother of Dædalus, though others in the running are Alcippe and Iphinoë. Sisyphus founded the city of Ephyre (Corinth) and later revealed Zeus's rape of Ægina to her father Asopus (a river), for which Zeus condemned Sisyphus to roll a huge stone up a hill in Hades, only to have it roll back down each time the task was nearly done. Glaucus (or Glaukos) was father of Bellerophon, and in one story was killed by horses maddened by Aphrodite because he would not let them breed. He also led Lycian troops in the Trojan War, and in the Iliad was tricked by the Greek hero Diomedes into exchanging his gold armor for Diomedes' brass, the origin of the term `Diomedian swap'. Another Glaucus was a fisherman of Boeotia who became a sea-god gifted with prophecy and instructed Apollo in soothsaying. Still another Glaucus was a son of Minos who drowned in a vat of honey and was revived by the seer Polyidos, who instructed Glaucus in divination, but, angry at being made a prisoner, caused the boy to forget everything when Polyidos finally left Crete. The word glaukos means gleaming, bluish green or gray, perhaps describing the appearance of a blind eye if glaucoma (cataract) derives from it. Is the name Glaucus a reference to sight, or blindness, physical or otherwise? It is also curious that meropia is a condition of partial blindness.

Another Merope was daughter of Dionysus's son Oenopion, king of Chios; Orion fell in love with her, and Oenopion refused to give her up, instead having him blinded. Orion regained his sight and sought vengeance, but was killed by Artemis, or by a scorpion, or by some other means (many versions).>>
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<<* Taygete or Taygeta - ? tanygennetos, `long-necked' -

Seduced by Zeus and gave birth to Lacedæmon, founder of Sparta, to which she was thus an important goddess. In some versions of the story, she was unwilling to yield to Zeus, and was disguised by Artemis as a hind (female red deer) to elude him; but he eventually caught her and begot on her Lacedæmon, whereupon she hanged herself.

Another Taygete was niece to the first. She married Lacedæmon and bore Himerus, who drowned himself in a river after Aphrodite caused him to deflower his sister Cleodice. One of the Taygetes may have been mother to Tantalus, who was tormented in Hades with thirst and hunger for offending the gods; however his parentage is uncertain; his mother may instead be Pluto (not the Roman version of Hades), daughter of either Cronus and Rhea or Oceanus and Tethys, and his father Zeus or Tmolus.>>
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<<* Asterope or Sterope - `lightning', `twinkling', `sun-face', `stubborn-face' (Indo-European ster-, `star', `stellar', `asterisk', etc.) -

In some accounts, ravished by Ares and gave birth to Oenomaus, king of Pisa. In others, Oenomaus was her husband, and they had a beautiful daughter, Hippodaima, and three sons, Leucippus, Hippodamus, and Dysponteus, founder of Dyspontium; or, Oenomaus may instead have had these children with Euarete, daughter of Acrisius.

Another Asterope was daughter of Porthaön, and may have been the mother of the Sirens, who lured sailors to their deaths with their enchanting singing.

A possible alternate name is Asterië (`of the starry sky' or `of the sun'), which may also be a name for the creatrix of the universe, Eurynome, in the Pelasgian myth. Graves mentions her as a Pleiad only in passing, with no other mention in the other references. Perhaps she was at one time a Pleiad when different names were used, or an earlier version of Sterope, whose name is similar; or perhaps Graves is incorrect. He also in passing calls the titan or oak-goddess Dione a Pleiad, without explanation or corroboration.>>
-------------------------------------------
<<* Celæno - `swarthy' -

Had sons Lycus (``wolf'') and Chimærus (``he-goat'') by Prometheus.>>
______________________________
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[sfcraiger]

todays camera resolution is so much better

[Chris Peterson]

todays camera resolution is so much better

Actually, camera resolution hasn't much changed. Modern electronic detectors have about the same resolution as film. More recent detectors have more pixels than older ones, but that isn't the same as resolution (even though in the world of conventional photography they are often considered the same).

Electronic detectors have a different character of resolution than film, because their pixels are independent. On film, local regions interact, and the resolution at a small scale is dependent on contrast. That's one reason that electronic detectors deliver more accurate data.

The real improvement that CCDs deliver over film, however, in in terms of dynamic range and linear response. And the change in CCDs over time has been greater dynamic range because of reduced noise. What this means is that modern cameras can essentially collect light from an object for an arbitrary length of time, steadily increasing dynamic range and reducing noise. This can be done selectively through specially designed filters, allowing for almost arbitrarily deep images that capture both bright regions and the very faint. This is something that simply wasn't possible with film.

Much of the improvement we've seen over the last 20 years in CCD images has much less to do with improvements in technology than it does with improvements in the skill of imagers in collecting and in processing the data.