Sunday, December 31, 2006

Happy New Year!

To all my friends (and you know who you are) in the astronomy-blog world. May this new year bring you health, happiness and all the good things in life.

Focus on Taurus

The Pleiades star cluster, also known as the Seven Sisters and Messier 45, is a conspicuous object in the night sky with a prominent place in ancient mythology. The cluster contains hundreds of stars, of which only a handful are commonly visible to the unaided eye. The stars in the Pleiades are thought to have formed together around 100 million years ago, making them 1/50th the age of our sun, and they lie some 130 parsecs (425 light years) away. From our perspective they appear in the constellation of Taurus, with approximate celestial coordinates of 3 hours 47 minutes right ascension and +24 degrees declination. For northern hemisphere viewers, the cluster is above and to the right of Orion the Hunter as one faces south, and it transits -- reaches its highest point in the sky, midway between rising and setting -- around 4am in September, midnight in November, and 8pm in January.


ALDEBARAN (Alpha Tauri). Aldebaran is by far the brightest, and therefore the Alpha, star of the constellation Taurus. The ancient name, from Arabic, means "the Follower," as the star seems to follow the Pleiades, or Seven Sisters star cluster, across the sky. Aldebaran, 60 light years away, is positioned in front of the sprawling Hyades star cluster (in mythology, half-sisters to the Pleiades) that make the face of Taurus the Bull, but is not a part of it, the cluster over twice as far away. In most renderings of the constellation, Aldebaran makes the celestial Bull's eye. As part of a constellation of the zodiac, Aldebaran is close to the Sun's path, the Sun passing to the north of it about June 1, the star also regularly covered, or occulted, by the Moon. This class K star, of first magnitude and 13th brightest in the sky, is a low- level irregular variable star that fluctuates erratically and to the eye unnoticeably by about two-tenths of a magnitude. Aldebaran's surface temperature of just under 4000 degrees Kelvin (compared to the Sun's 5800 degree temperature) gives it a distinct orangy color. It is a giant star, a star in an advanced state of evolution in which the interior hydrogen fuel has run out, the star now running on the fusion of helium into carbon. Some 350 times more luminous than the Sun, it has expanded to a radius about 40 times solar, making it big enough to enable astronomers to measure its small angular diameter of only 0.021 seconds of arc (the apparent size of a US nickel seen at a distance of 50 kilometers). This large star is an extremely slow rotator, taking almost two years to make a full spin. If placed at the position of the Sun, Aldebaran would extend halfway to the planet Mercury and would appear 20 degrees across in our sky, making life on Earth quite impossible. Yet Aldebaran may have its own "solar system." Recent, though still-unconfirmed, observations show that the star may be slightly shifting back and forth in response to a small body with a mass at least 11 times that of Jupiter and a two-year orbital period. We do not yet know if the body -- if it exists at all -- is a massive planet or a low-mass "brown dwarf," a failed star that is too small to run supporting thermonuclear reactions in its core.

Source: Jim Kaler, Professor Emeritus of Astronomy, University of Illinois

Friday, December 29, 2006

Missing Old Friends

It's been a while since I've seen some of my old friends - and I'm missing them! The clear -well sometimes- nights in January is the best month for visiting with them.

I'm talking about stars people! I can't wait to see them again so I must start planning now.

Thursday, December 28, 2006

Today in Astronomy History

Thomas Henderson 1798-1844

Scotland's First Astronomer Royal

Of all the Astronomers Royal for Scotland, only 3 were Scots, and of these 2 were born in Dundee - Thomas Henderson and Malcolm Longair. Henderson was born on 28 December 1798, the younger son of a tradesman, and educated at Dundee Academy under Thomas Duncan, rector, (later Professor of Mathematics at St Andrews) where he showed a great aptitude for mathematics and science. At 15 he entered a Dundee law office, was promoted to Edinburgh, and eventually became Secretary to the Earl of Lauderdale then to the Lord Advocate.

In Edinburgh he had access to the Observatory of the Astronomical Institution on Calton Hill, which was frequented by various city notables and gentry, and was encouraged by Professors William Wallace and John Leslie to use the modest instruments. On frequent visits to London on legal business he made friends with several astronomers including G. B. Airy, John Herschel and Sir James South who gave him full use of his observatory at Camden Hill. But Henderson had poor eyesight, perhaps a squint, and decided to concentrate on mathematical astronomy rather than observing. In a number of papers he demonstrated computational methods used in Germany but not then common in Britain, and began to be noticed by the astronomers of the Nautical Almanac, Board of Longitude and the Royal Astronomical Society. In 1830 he compiled a list of moon-culminating stars (for determining longitudes by lunar distances) for Sir John Ross's Arctic expedition.

He was turned down as a candidate for the vacant Chair of Astronomy at Edinburgh, (it was under threat of abolition, the previous incumbent, Robert Blair, having treated it as a sinecure for 42 years) and as Superintendent of the Nautical Almanac, but friends persuaded him to accept the post of Astronomer at the Cape of Good Hope. From April 1832 to May 1833, with one assistant, Lieutenant Meadows, and with indifferent instruments, he carried out a prodigious observing programme including a catalogue of the positions of southern stars, estimates of the distance of the sun and moon and observations of comets.

At the Cape he began observations of the exact position with respect to the surrounding stars of the bright star Alpha Centauri which a fellow astronomer had pointed out to him had an unusually high Proper Motion, i.e. its movement against the sky background, although in itself this was very tiny. Henderson surmised that it might be a close star. However, he resigned in 1833 with his health shattered and having had enough of the "dismal swamp" among "slaves and savages".

He returned to Edinburgh, subsisting on a small pension from his legal firm, and calculated his Cape results. The position of Alpha Centauri showed a residual error of about one second of arc (1/3600 of a degree, or 1/1800 of the moon's angular diameter) which was confirmed by observations of the star at the Cape by his successor Thomas Maclear. This was concluded to be the angle of parallax of the star against the background of distant stars, caused by the motion of the earth round the sun, and therefore the first estimate of the distance of a star at about 3.25 light years. (A later measurement gave 0.75 seconds of arc, at about 4.5 light years.) However, the great German mathematician Friedrich Wilhelm Bessel of Konigsberg, working independently and with a much superior instrument and a different method, announced a parallax for 61 Cygni, a somewhat more distant star in the northern hemisphere, 2 months before Henderson, and thereby got the Gold Medal of the Royal Astronomical Society and all the credit. Henderson had been cautious because his instrumentation was suspect, he needed confirming observations and he feared ridicule because false parallaxes had been announced before. Despite this Henderson and Bessel became friends and even holidayed in Scotland together.

In 1834 the Astronomical Institution of Edinburgh was in financial trouble. It was arranged that the Calton Hill Observatory be taken over by the government to run as a state establishment with the Observer to be jointly Regius Professor in Edinburgh University and Astronomer Royal for Scotland. Henderson was duly elected, supported by his many distinguished friends, and during the last 10 years achieved another prodigious workload with the help of his assistant Alexander Wallace, although he did very little teaching. He made some 60,000 observations, which amazed his successor Charles Piazzi Smyth, and many were published in the first volumes of The Edinburgh Astronomical Observations, but later errors were found, caused by the irregular thermal expansion of the stone pillars of the Fraunhofer transit telescope. He was a Fellow of the Royal Societies of Edinburgh and of London, but never took a degree.

But the daily climb up the hill from his official residence at 1 Hillside Crescent, and the death of his wife in 1842, were too much for a frame already weakened by heart disease. He died on 23 November 1844 and is buried in an almost forgotten corner of Greyfriars Churchyard. There is a memorial tablet to him on the west side of the Playfair Building. No proper portrait of him is known to exist.

Wednesday, December 20, 2006

Catching the Light

I really enjoy looking at photos others have taken of the heavens and I admire anyone who has the patience to go out there and give astro-photography a go.

Here’s a link to a great site. Catching the Light.

Tuesday, December 19, 2006

Meteor Showers 2007



January 3-4

Frequency: 31-45 per hour
99.8% illumination
Typically, 40 or so bright, blue and fast (25.5 miles per second) meteors will radiate from the constellation Bootes, some blazing more than halfway across the sky. A small percentage of them leave persistent dust trains. This shower usually has a very sharp peak, usually lasting only about an hour.
Parent Comet: 2003 EH1



April 21-22

Frequency: 16-30 per hour
26.3% illumination
The swift and bright Lyrid meteors disintegrate after hitting our atmosphere at a moderate speed of 29.8 miles per second. They often produce luminous trains of dust that can be observed for several seconds.
Parent Comet: C/Thatcher


Eta Aquarids

May 5-6

Frequency: 0-15 per hour
88.2% illumination
Parent Comet: 1P/Halley



June 14-16

Frequency: 0-15 per hour
0% illumination
The June Lyrids is a low-rate shower during which you could see up to 10 meteors per hour during its peak.


Delta Aquarids

July 28-29

Frequency: 16-30 per hour
98.1% illumination
At peak time about 20 bright, yellow meteors can be observed per hour. Because these meteors nearly broadside the Earth, their speed is a moderate 25.5 miles per second.


July 29-30

Frequency: 0-15 per hour
99.4% illumination
The Capricornids are characterized by their often yellow coloration and their frequent brightness. They are also slow interplanetary interlopers, hitting our atmosphere at around 15 miles per second. Though you can expect only 15 meteors per hour at best under dark sky conditions, the Capricornids are noted for producing brilliant fireballs.



August 12-13

Frequency: 45+ per hour
1.3% illumination
This shower produces about 60 meteors per hour, and its performance is farily consistant from year to year.
Parent Comet: 109P/Swift-Tuttle



October 8-9

Frequency: 0-15 per hour
5% illumination
Expect a peak rate of 10 meteors per hour under clear, moonless conditions.
Parent Comet: 21P/Giacobini-Zinner


October 21-22

Frequency: 16-30 per hour
75.3% illumination
This shower produces a peak rate of 20 yellow and green meteors per hour, which are fast moving at 41.6 miles per second and are known to produce fireballs.
Parent Comet: 1P/Halley



November 17-18

Frequency: 31-45 per hour
50% illumination
The Leonids are best known for their 33-year peaks, during which 100s of meteors per hour can be observed. The last of these peaks occured in 2001.
Parent Comet: 55P/Tempel-Tuttle



December 13-14

Frequency: 45+ per hour
15.9% illumination
The most reliable meteor shower of the year, the Geminids are characterized by their multi-colored display--65% being white, 26% yellow, and the remaining 9% blue, red and green.
Parent Comet: 3200 Phaethon

Source: Skyscrapers, Inc.

Monday, December 18, 2006

Ice Age Map of the Night Sky

A painted map of the prehistoric cosmos is on the wall of a famous Ice Age cave at Lascaux in central France.

Cro-magnon man — distant ancestors of humans living much later than the earlier Neanderthals and Aurignacians — painted the Lascaux caves with drawings of bulls, horses and antelope some 16,500 years ago. Thus, the map may be 16,500 years old.

The Ice Ages were cold periods in ancient history when glaciers descended across the northern continents and then receded. The temperatures experienced by humans and their ancestors alternated between cold and warm. Scientists say there have been at least four Ice Ages. Today, when people speak of "the Ice Age," they usually refer to the most recent glacial period, which ended about 8,000 years ago.

Summer Triangle. The painted walls of the Lascaux caves were discovered in 1940. The sky map was identified year later in a region of the Lascaux caves known as the Shaft of the Dead Man. Painted on to the wall of the shaft is a bull, a strange bird-man and a mysterious bird on a stick.

Since it was in the time we call pre-history — before people started recording history — no one knows if a cave could have been used as a kind of planetarium where stars were charted.

European researcher Michael Rappenglueck, however, suggests that it is a map of three particular stars — Vega, Deneb, Altair — that astronomers today refer to the Summer Triangle. Those stars are among the brightest objects in the sky during the middle of a northern summer. Rappenglueck sees the eyes of the bull, bird-man and bird as representing Vega, Deneb and Altair.

Source: Space Today Online

Saturday, December 16, 2006

Heavyweight Stars Light Up Nebula NGC 6357

The small open star cluster Pismis 24 lies in the core of the large emission nebula NGC 6357 in Scorpius, about 8,000 light-years away from Earth. Some of the stars in this cluster are extremely massive and emit intense ultraviolet radiation. The brightest object in the picture is designated Pismis 24-1. It was once thought to weigh as much as 200 to 300 solar masses. This would not only have made it by far the most massive known star in the galaxy, but would have put it considerably above the currently believed upper mass limit of about 150 solar masses for individual stars. However, high-resolution Hubble Space Telescope images of the star show that it is really two stars orbiting one another (inset pictures at top right and bottom right). They are estimated to each be 100 solar masses. The Hubble Advanced Camera for Surveys images were taken in April 2006.

Source: The Hubble Site