Our spring almanac 14.05.2010 – 20.05.2010

One Swallow does not make a summer

One swallow does not make a summer, nor does one day; and so too one day, or a short time, does not make a man blessed and happy. So said the Greek philosopher and scientist Aristotle.

The Barn Swallow migrates from Africa to spend the spring and summer here in southern England. Migration of Barn Swallows between Britain and South Africa was first established on 23 December 1912 when a bird that had been ringed by James Masefield at a nest in Staffordshire, was found in Natal nearly 6000 miles from here. For people living in South Africa the month of May is not a month for looking forward to summer, winter is coming, which is probably good for the national football teams training for the World Cup. In southern Africa, which is in the southern hemisphere of our planet, the seasons are the opposite of the ones we have here. During May, June and July, the northern hemisphere is exposed to more direct sunlight because the hemisphere faces the sun. The same is true of the southern hemisphere in November, December and January.

It is the tilt of the Earth that causes the Sun to be higher in the sky during the summer months which increases the solar flux. However, due to seasonal lag, June, July and August are the hottest months in the northern hemisphere and December, January and February are the hottest months in the southern hemisphere.

Morgaston Woods
Swallows usually appear in April, but this year have only become more noticeable as we move into the middle of May. This year most of the signs of spring have been late, all catching up during this month of May. The appearance of bluebells and daisies for instance.

Canis Major

Canis Major has a deep sky object in Messier 41 (also known as M41 or NGC 2287). It is an open cluster discovered by Giovanni Batista Hodierna before 1654 and was perhaps known to Aristotle about 325 BC.

M41 lies about four degrees almost exactly south of Sirius. It contains about 100 stars including several red giants, the brightest being a spectral type K3 giant near the cluster’s center. A Red Giant is a luminous giant star of low or intermediate mass (roughly 0.5–10 solar masses) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower. The appearance of the red giant is from yellow orange to red, including the spectral types K and M, but also class S stars and most carbon stars.

At some point in the Sun’s future evolution it will become a Red Giant.

Sirius is the brightest star in the night sky of earth. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name “Sirius” is derived from the Ancient Greek Seirios (“scorcher”).

What is visible to the naked eye as a single star is actually a binary star system, consisting of a white main sequence star of spectral type A1V, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B.

Sirius is also known colloquially as the “Dog Star”, reflecting its prominence in its constellation, Canis Major (English: Big Dog). The heliacal rising of Sirius marked the flooding of the Nile in Ancient Egypt and the “Dog Days” of summer for the Ancient Greeks, while to the Polynesians it marked winter and was an important star for navigation around the Pacific Ocean.

Navigation by the stars

Sirius, being the brightest star, is one of the so called navigational stars used in celestial navigation. Celestial navigation, also known as astronavigation, is a position fixing technique that has steadily evolved over several thousand years to help sailors cross featureless oceans without having to rely on estimated calculations, or dead reckoning, to enable them to know their position on the ocean. Celestial navigation uses “sights,” or angular measurements taken between a visible celestial body (the sun, the moon, a planet or a star) and the visible horizon.

The angle measured between the sun and the visible horizon is most commonly used. Skilled navigators can additionally use the moon, a planet or one of 57 navigational stars whose coordinates are tabulated in the Nautical Almanac and Air Almanacs. Seafarers have used these stars through the ages, so the list of 57 stars that navigators use comes to us through the practice of their skills over thousands of years.

Nautical Almanac

A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea. The Almanac specifies for each whole hour of the year the position on the Earth’s surface (in declination and Greenwich hour angle) at which the sun, moon, planets and first point of Aries is directly overhead. The positions of 57 selected stars are specified relative to the first point of Aries.

Prior to the introduction of electronic means of navigation the only way to fix an aircraft’s position at night was by taking star sights using a sextant in the same manner as that used by marine navigators on board ships.

To do this requires a 360-degree view of the horizon and the astrodome was devised to allow an uninterrupted view of the sky from horizon to horizon. Hence the astrodome is a hemispherical transparent dome fitted in the cabin roof of an aircraft for the purpose of allowing the use of a sextant during astro-navigation.

The Jewish festival of Shavuot is also known as the festival or feast of ‘Weeks’. There is no set date for the two-day festival, but it takes place seven weeks (fifty days) after the first day of the spring festival of Passover which falls this year on May 19. This also marks the start of the wheat harvest and the end of the barley harvest.

High places
Shavuot marks the time that the Jews received the Torah on Mount Sinai. It is considered a highly important historical event. The tablets of stone inscribed with the 10 Commandments were, according to traditional teachings of Judaism in the Talmud, made of blue sapphire stone as a symbolic reminder of the sky, the heavens, and ultimately of God’s throne.

The Christian festival of Pentecost also comes from Shavuot. St Catherine’s Monastery at the foot of Mt. Sinai is one of the oldest surviving Christian communities.

Prayers are said on Shavuot (especially at dawn) to thank God for the five books of Moses (collectively known as the Torah) and for his law. Some people also spend the first night of Shavuot studying the Torah. Synagogues are decorated with flowers and plants on this joyous occasion to remember the flowers of Mount Sinai. Dairy products are also eaten during Shavuot. There are many interpretations about why this custom is observed. It is believed that once the rules about the preparation of meat were revealed in the Torah, the people of Sinai were reluctant to eat meat until they fully understood the rules.

In the last post we included Ascension Day that marks the last earthly appearance of Christ after his resurrection celebrated 40 days after Easter. The Catholic Church in England and Wales celebrates it on the following Sunday 16 May instead.

Final ascent
On May 14, 2010 the Space Shuttle Atlantis lifted off into space for its final voyage during which it will visit the International Space Station.

Two spacewalking astronauts began a tricky battery swap on the space station’s solar arrays Wednesday, a job that is expected to take two full spacewalks to complete.

Atlantis mission specialists Michael Good and Stephen Bowen got ahead of schedule, successfully installing more than half of the new batteries. In addition, they were able to fix a snagged cable that was plaguing a sensor camera on shuttle Atlantis and tighten the connection between a stuck antenna and its stand.

South View 20.05.2010


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