THE SOUTHWORTH PLANETARIUM
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Founded January 1970
Julian date: 2457874.16
“To be beautiful means to be yourself. You don’t need to be accepted by others. You need to accept yourself.” ~Thich Nhat Hanh
THE DAILY ASTRONOMER
Monday, May 1, 2017
Week 33 Night Sky Calendar
May 1 - 7, 2017
CONSTELLATION OF THE WEEK:
HYDRA - THE LONGEST OF THEM ALL
It is said that half of the sky was slain by Hercules. While this statement is a slight exaggeration, it is certainly true that some of Hercules' kills now adorn the firmament. Hydra the water snake is an example of one such creature which Hercules sent careening into the underworld, only to be elevated into the heavens.
The Learnaean Hydra was one of the many creatures sired by Typhon and Echdina, the half-nymph/half serpent creature known as the "mother of monsters." (She also gave birth to such cuties as Cerberus, the three headed hound guarding the underworld; the Chimera, the Caucasian Eagle that fed on Prometheus' liver, and the Sphinx, among others.) The Hydra resided in the lake of Lerna, south of Argos. This monstrously evil creature was said to have been so vile that her very blood was a lethal poison and its breath could kill most mortals. Moreover, this serpentine beast had multiple heads which, if removed, would merely sprout two other heads and an immortal head that could not be destroyed. Hydra terrorized the Lernan lake people who were often slain merely by coming close to it.,
HYDRA THE WATER SNAKE The Learnean Hydra was said to have been so toxic that even her breath could prove fatal. This fearsome many-headed water snake was also self-regenerative. The removal of one head merely precipitated the formation of two others. Hercules managed to slay this monster with the aid of his nephew,I olaus, who cauterized the stumps with an iron, thereby preventing the regrowth of the two heads. IMAGE: SKY AND TELESCOPE (IAU)
Eurystheus, king of Tirys/Mycenae, sent Hercules to slay the Hydra as the second of his twelve labors. Hercules quickly found Hydra and, being intrepid, cornered the beast in its lair. Hercules then deftly maneuvered around the many heads while lopping them off. He soon realized, however, that Hydra had merely responded to these decapitations by sprouting more heads. Fortunately, Hercules had been accompanied by his nephew Iolaus who, at his uncle's instruction, started to cauterize the stumps after each beheading to prevent the formation of other heads. Consequently, Hercules soon destroyed all the heads save for the immortal one. The warrior ultimately removed the head at the base of the neck and buried it under a rock. Being ever resourceful, Hercules dipped his arrow tips in the Hydra's blood, rendering them so poisonous that even a nick from one of the arrows proved inevitably fatal.
Hera placed Hydra in the night sky as a tribute, for it was a formidable creature which earnestly attempted to kill Hercules. Because Hydra was unsuccessful, its stars are faint. However, because the battle it waged against Hercules lasted longer than almost any other fight he ever experienced before or after, Hydra was allotted a large swath of the sky. In fact, Hydra encompasses 1302 square degrees in the sky, making it the largest of all eighty eight constellations.
Hydra also supplies us with three more Messier objects (M48, M68 and M83), which we will feature at different places in this week's night sky calendar.
MONDAY, MAY 1: MAY DAY (BELTANE) CROSS QUARTER DAY
Our calendar recognizes four cross-quarter days, those days that are midway between successive seasonal dates. Imbolc, or Ground hog's Day (Feb 2) is the cross quarter day between the winter (December) solstice and vernal (March) equinox. Beltane or May Day (May 1) marks the mid point between the vernal equinox and summer (June) solstice. Lammas (August 1) is the cross quarter day between the summer solstice and autumnal (September) equinox. Finally, Sahmain or Halloween (October 31) is the mid point between the autumnal equinox and winter solstice.
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M48: ONE OF THE "LOST" CLUSTERS
Astronomers recognize two main star cluster types: open, or galactic clusters, and the much larger and older globular clusters. We can also see many galactic clusters with the naked eye because many of them are rather close. M48, a galactic cluster within Hydra, is 1,500 light years away and visible without a telescope in the darkest skies. The cluster contains about a hundred members scattered over a spherical region twenty-three light years in diameter.
Charles Messier first observed this cluster in 1771 and designated it as M48. However, his position was about five degrees away from its currently accepted location. For this reason, M48 was considered one of the lost clusters, until it was determined that Charles Messier had observed this cluster, but mistakenly placed it elsewhere in the sky.
IMAGE: Ole Neilsen
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TUESDAY, MAY 2: MERCURY STATIONARY
With an average orbital velocity exceeding 160,000 miles per hour, Mercury is one father of a mover.! Of course, this planet has the location advantage, as it is the closest planet to the Sun. The closer a planet is to the Sun, the faster the planet revolves around it. Like all planets, Mercury experiences prograde motion (west to east) and then retrograde motion (east to west.) A planet will appear to switch from one to the other just after its stationary period. Mercury has been moving in a retrograde manner and will now resume prograde motion.
We know that Mercury isn't stopping, of course. Instead, we're seeing Mercury reach one "end" of its orbit from our perspective. It is like a spectator watching cars racing around a track. When a car is turning around the curve at either end of the track, the spectator doesn't see it moving either left or right, but either back and forth. Earth observers cannot see a planet moving radially (toward or away from us), but only in a transverse way (prograde and retrograde.)
TUESDAY, MAY 2: FIRST QUARTER MOON
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M68: A Far Flung Globular Cluster
Globular clusters travel around the galactic nucleus in much the same way as comets move around the Sun. Of course, globulars have orbital periods exceeding a million years, whereas even the longest period comets require tens or hundreds of thousands of years to complete one orbit.* Globular cluster M68 moves along a highly eccentric orbit which can convey it more than 100,000 light years from the nucleus it orbits. Presently, this extremely rich cluster is 33,000 light years from Earth. The above image, captured by the Hubble Space Telescope, shows a dense cluster surrounded by a loose aggregation of stars. M68 could be experiencing a slow core collapse, but astronomers aren't certain if this collapse is actually occurring.
Charles Messier first observed this rich cluster in 1780.
IMAGE: Hubble Space Telescope
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SUNDAY, MAY 7: JUPITER 2 DEGREES SOUTH OF THE MOON (BRONZE EVENT!)
How lovely! The gibbous moon (90% illuminated) and the brilliant planet, Jupiter traveling together throughout the night. Recall that the moon moves about half a degree an hour (equal to its own angular diameter), so the 2 degree separation will be short-lived. Watching Jupiter and the moon throughout the evening allows an observer to measure the moon's motion relative to Jupiter which, though not stationary, maintains almost the same position over the course of an evening.
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M83: The "Southern Pinwheel" Galaxy
You might have heard of M101, the "Pinwheel Galaxy" within Ursa Major. M83, in Hydra, is the "Southern Pinwheel." At a distance of 15 million light years. M83 is one of the closest barred spiral galaxies to the Milky Way. Consequently, it is also one of the most closely studied barred spirals. Astronomers have observed more than six supernovae within this galaxy. Also, NASA's Galaxy Evolution Explorer detected an abundance of stars along the outer part of the galaxy, a region once thought too devoid of gases to permit star formation/
Although French astronomer Nicolas Louis de Lacaille discovered this galaxy in 1752, Charles Messier didn't include it in his catalog until 1781. Lacaille observed it from the Cape of Good Hope and, lacking the rapid means of communication we take for granted today, it took awhile for Messier to become aware of this celestial object's discovery.
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PLANET WATCH
MERCURY is a moderately bright pre-dawn eastern sky object throughout May and into June. Throughout the first half of May, Mercury arches higher in the eastern sky. On May 17th, Mercury reaches greatest western elongation (26 degrees). VERDICT: May is a good month for Mercury admirers. However, one would be advised to wait until the second week of the month, when it will be higher above the eastern horizon and easier to find.
VENUS will remain as a morning sky object until November, affording early morning observers ample opportunity to admire this glimmering spectacle of a planet. As always, Venus outshines all the other planets and night sky stars. Venus reaches greatest western elongation on June 3rd. VERDICT: A beautiful beacon for morning sky watchers. Venus climbs higher throughout the month.
MARS will remain in the western evening sky until mid June, after which time it won't be visible again until it re-emerges into the September morning sky. VERDICT: Mars will be easier to find in May than June, so try to find the red world this month. After all, Mars will be gone almost all summer. Catch it while you can.
(PICK PLANET!) JUPITER reached opposition on April 7th, around which time the giant planet was also at its brightest. Although Jupiter is slowly diminishing in brightness, it remains more than twice as bright as Sirius, the night sky's brightest star. Jupiter will remain in our evening sky until mid October, when it vanishes into the dusk. VERDICT: Jupiter is still a brilliant evening sky planet. Just venture outside after night fall and find the giant world high and bright in the eastern sky!
SATURN rises earlier and grows steadily brighter throughout the month as it approaches its June 15th opposition date. Although not yet visible after dusk, Saturn appears soon after nightfall and remains above the horizon for the remainder of the night. Saturn will serve as a moderately bright evening sky beacon until early December, when it disappears into the dusk VERDICT: One doesn't have to stay out late to see Saturn. However, if you want to wait until later this summer, do so. Saturn will be easiest to find in mid June, when it is at its brightest and up all night.
*Comet Hyakutake, first seen in 1996, has an orbital period of approximately 70,000 years. Comet West, discovered in 1975, has an orbital period of nearly half a million years.
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