Our summer almanac 23.07.2010 – 29.07.2010




Vega
Our summer almanac makes mention of Vega (α Lyr / α Lyrae / Alpha Lyrae) regularly as it is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus. It is a relatively close star at only 25 light-years from Earth, and, together with Arcturus and Sirius, one of the most luminous stars in the Sun’s neighborhood.

The name of this star comes from a loose transliteration of the Arabic word wāqi‘ meaning “falling” or “landing”, via the phrase an-nasr al-wāqi‘ “the alighting vulture”. The constellation was represented as a vulture in ancient Egypt, and as an eagle or vulture in ancient India.

Vega has been extensively studied by astronomers, leading it to be termed “arguably the next most important star in the sky after the Sun.” Vega was the northern pole star around 12,000 BC and will be so again around AD 13,727 when the declination will be +86°14′. Vega was the first star other than the Sun to be photographed and the first to have its spectrum recorded. It was one of the first stars whose distance was estimated through parallax measurements.

Stars, dust and debris
Vega is an interesting star in the discovery of excess infrared flux coming from Vega, beyond what would be expected from the star alone in one of the early results from the Infrared Astronomy Satellite (IRAS). The Infrared Astronomical Satellite[2] (IRAS) was the first-ever space-based observatory to perform a survey of the entire sky at infrared wavelengths.

Launched on January 25, 1983, its mission lasted ten months. The telescope was a joint project of the United States (NASA), the Netherlands (NIVR), and the United Kingdom (SERC).

Following the discovery of an infrared excess around Vega, other stars have been found that display a similar anomaly that is attributable to dust emission. As of 2002, about 400 of these stars have been found, and they have come to be termed “Vega-like” or “Vega-excess” stars. It is believed that these may provide clues to the origin of the Solar System.

By 2005, the Spitzer Space Telescope had produced high resolution infrared images of the dust around Vega. It was shown to extend out to 43″ (330 AU) at a wavelength of 24 μm, 70″ (543 AU) at 70 μm and 105″ (815 AU) at 160 μm. These much wider disks were found to be circular and free of clumps, with dust particles ranging from 1–50 μm in size. The estimated total mass of this dust is 3 × 10−3 times the mass of the Earth. Production of the dust would require collisions between asteroids in a population corresponding to the Kuiper Belt around the Sun. Thus the dust is more likely created by a debris disk around Vega, rather than from a protoplanetary disk as was earlier thought.

Artist’s concept of a recent massive collision of dwarf planet-sized objects that may have contributed to the dust ring around the star Vega.

Dark Matter and Shooting Stars
From July 27 until August 17 it is worth looking out for the meteor shower called the Perseids. Look toward the north east after midnight and see if you can find the constellation Perseus. It is because these shooting stars appear in a part of the night sky close to this constellation that this meteor shower is called the Perseids.

When we look out at our Universe we see stars and galaxies, and the more we explore deep into space, the more we find, but there is also a lot more mass and material in the Universe we cannot see. Even though we can’t see this mass and material, astronomers have calculated that it must be there having observed the gravitational motions of stars and galaxies, and that this missing mass must be about 20 times the amount visible as starlight.

Astronomers and cosmologists call this missing mass ‘Dark Matter’. This ‘missing matter’ was first discovered in the 1920’s when a Dutch astronomer called Jan Oort was measuring the speed of stars as they move in the disc of our galaxy. He was expecting to find them moving up and down in the galactic disc as they turn with the galaxy. He found that stars do indeed move in this way, but not as much as he expected, so he concluded that there must be a lot more matter in the disc of the galaxy than had previously been calculated. Jan Oort worked out that if the disc of the Milky Way had about 50% more matter than previously anticipated, then that would explain the movement of the stars he had observed.

In the 1970’s and 80’s, the American astronomer Vera Rubin was looking at other galaxies, studying the speed of stars as they orbit around various galactic discs. She expected to find that the further out from the centre stars were, the slower the star speeds would be. Instead they found that the orbital speed of stars was more or less constant. From this discovery they calculated that each galaxy must be surrounded by a halo of invisible material, weighing 10 times as much as the bright disc. What this dark matter actually is still puzzles astronomers and cosmologists today, but there are some very interesting theories and experiments going on to try and answer this question.

Dharma day
Dharma day on July 26 marks the beginning of the Buddha’s teaching. The word Dharma can be translated as truth and is the term used for the path to enlightenment, or the Buddhist teaching. Soon after his Enlightenment the Buddha went to find his former disciples and share his experience with them. This event could be seen as the start of the Buddhist religion, and is what Dharma day celebrates.

The first teaching to the Buddha’s original five disciples is known as “The First Turning of the Wheel of the Dharma (Dharmachakra).”

In early Buddhism, the time around what has now become Dharma Day (the eighth lunar month in the traditional Indian calendar) marked the beginning of the rainy season. At this point, the Buddha and his monks and nuns would suspend their nomadic lifestyle for three months. They would shelter together until the monsoon season was over, and use this time as a period of further meditation and reflection. At the end of this time, they would resume their travelling, passing on the Buddha’s teachings to those who were interested.

Dharma day is now seen as a chance to express gratitude that the Buddha, and other enlightened teachers, have shared their knowledge with others. Dharma day is usually celebrated with readings from the Buddhist scriptures, and is an opportunity to reflect deeply on their content.

Monsoon rains in modern Varanasi

Rainy seasons at home and away
Our wet weather days are connected to rainfall and heatwaves across the globe by the jet stream. The publication New Scientist makes connections between the floods and forest fires with our own dreary wet summer days:

Raging wildfires in western Russia have reportedly doubled average daily death rates in Moscow. Diluvial rains over northern Pakistan are surging south – the UN reports that 6 million have been affected by the resulting floods. It now seems that these two apparently disconnected events have a common cause. They are linked to the heatwave that killed more than 60 in Japan, and the end of the warm spell in western Europe. The unusual weather in the US and Canada last month also has a similar cause. According to meteorologists monitoring the atmosphere above the northern hemisphere, unusual holding patterns in the jet stream are to blame. As a result, weather systems sat still. Temperatures rocketed and rainfall reached extremes.

Monsoon winds are getting stronger as the northern hemisphere warms. Climate reconstructions reveal unprecedented warming in the last century, however little is known about trends in aspects such as the monsoon. Studies that have reconstructed the monsoon winds for the last 1,000 years using fossil Globigerina bulloides abundance in box cores from the Arabian Sea, found that monsoon wind strength has increased during the past 4 centuries, as the northern hemisphere has warmed.

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