Archive for September, 2010

Our autumn almanac 24.09.2010 – 30.09.2010

Posted in astronomical time on September 24, 2010 by espacelab

Discovery of a new Earth-like planet
At the end of this 7 day period of our autumn almanac came news of the discovery of a new Earth-like planet.

Astronomers have discovered a potentially habitable planet of similar size to Earth in orbit around a nearby star. A team of planet hunters spotted the alien world circling a red dwarf star called Gliese 581, 20 light years away. The planet is in the “Goldilocks zone” of space around a star where surface temperatures are neither too hot nor too cold for liquid water to form.

“Our findings offer a very compelling case for a potentially habitable planet,” said Steven Vogt, an astronomer at the University of California, Santa Cruz. “The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common.”

If confirmed, the planet would be the most Earth-like that has ever been discovered in another solar system and the first strong contender for a habitable one.

More than 400 exoplanets have been discovered by astronomers, but most are gas giants, like Jupiter, that would be inhospitable to life as we know it.

Sunset over four telescopes of the Mauna Kea Observatories. From left to right: the Subaru Telescope, the twin Keck I and II telescopes, and the NASA Infrared Telescope Facility.

Astronomers used the Keck telescope in Hawaii to study the movement of Gliese 581 in exquisite detail and from their observations inferred the presence of a number of orbiting planets. The team report two new planets in the Astrophysical Journal, bringing the total number known to be circling the star to six.

One of the planets, named Gliese 581g, has a mass of three to four times that of Earth and takes 37 days to orbit the star. Astronomers believe it is a rocky planet with enough gravity to retain an atmosphere.

Unlike the previously discovered planets, Gliese 581g lies squarely in the region of space were life can thrive. “We had planets on both sides of the habitable zone — one too hot and one too cold — and now we have one in the middle that’s just right,” Vogt said.

One side of the planet is always facing the star, much as one side of the moon constantly faces Earth. This means that the far side of the planet is constantly in darkness. The most habitable region of the planet would be the line between the light and dark regions.

“Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude,” Vogt said.

The average temperature on the planet is estimated to be between -31 to -12C, but the ground temperature would vary from blazing hot on the bright side and freezing on the dark side.

“The number of systems with potentially habitable planets is probably on the order of 10 or 20 percent, and when you multiply that by the hundreds of billions of stars in the Milky Way, that’s a large number. There could be tens of billions of these systems in our galaxy,” said Vogt.

Our autumn almanac 17.09.2010 – 23.09.2010

Posted in astronomical time on September 17, 2010 by espacelab

Autumn Equinox
Autumn begins on the equinox which takes place this year on 23 September at 03.09h GMT. So daylight lasts for 12 hours followed by 12 hours of night. Why do we have 24 hours in a day? More than 3000 years ago, in Egypt, the priests of Ra ruled that there would be 12 hours of the day and 12 hours of the night. Perhaps the ancient Egyptians had an obsession with the number 12 just like the Babylonians and the ancient Sumerians before them. The idea that counting began with the three sections of finger bone on each of four fingers, three times four making twelve, or the twelve constellations on the ecliptic, the path of the Sun across the heavens, so significant to Babylonian astrology, who knows?

The autumnal equinox is a good time to make a note of where east and west are on your horizon as you look out from where you live, because on this particular day the Sun rises due east and sets due west. Knowing where east and west, and therefore where north and south are, is very helpful in finding your way around the night sky when you are using a star map.

At this time of year the night sky seems to be full of the summer star patterns or constellations we could see a month ago. This is because the nights are falling much earlier as autumn begins and this means we still see the summer constellations in the evening sky as they move towards the west.

This time of year has more to do with harvest than summer. As the ancient Greek poet Hesiod has it: “when Orion and Sirius move into the middle of the sky, and the star Arcturus sees the rosy fingered dawn, then pluck the clustered grapes and bring your harvest home”.

Harvest Moon
This year we see the Harvest Moon rise at 9.20 on the same day as the equinox, a rather special event as the equinox will not fall at the same time as the harvest moon again until 2029.

When the Full Moon rises its brilliance brightens the fields of harvest all night long. In the days before the mechanization of agriculture the harvest was all collected by hand. Everyone was needed to bring the harvest home as quickly as possible, and the Harvest Moon allowed people to work in the field well into the evening and late into the night.

This special moon also marks Wednesday’s mid-autumn Festival, celebrated by Chinese people worldwide at this time of year. It’s a festival marked with round moon cakes and lanterns to represent the harvest moon. The shape of the full moon is significant, as the word “round” implies family reunion in Chinese.

The Craters of the Moon
This week NASA reported on their latest survey of the craters of the Moon using advanced measuring techniques using lasers.

The violent history of our nearest celestial neighbour has been laid bare by the most detailed map of moon craters ever produced.

Scientists used instruments aboard Nasa’s Lunar Reconnaissance Orbiter to scan the surface of the moon for impact craters measuring at least 20km wide.

Pictures sent back by the spacecraft revealed 5,185 large craters caused by lumps of space rock thumping into the lunar surface over the past few billion years. Some regions of the moon are so pocked with craters they have reached what planetary scientists call “saturation equilibrium”, where each additional crater wipes out an older one, so the number of craters remains the same.

The moon is thought to have formed 4.5 billion years ago, when a heavenly body the size of Mars struck Earth and dislodged an enormous cloud of debris that ultimately condensed into our planet’s natural satellite. By analysing the craters and their positions, the researchers determined that the oldest regions of the lunar surface were the southern areas that face Earth and the northern region of the far side of the moon. Some parts of the moon are younger than others because ancient volcanic eruptions spewed out material that covered vast areas of land and erased the craters that were there before.

The map confirms previous lunar surveys that found older parts of the moon’s surface have a greater number of craters than younger areas. This suggests the moon was pummelled with larger space rocks in its early life than it was later on.

One possible explanation is that fewer huge chunks of rock were flung out of the asteroid belt and onto a collision course with the moon once Jupiter and Saturn – the planets with the most mass and so the greatest gravitational pulls – had settled into their orbits.

Our summer almanac 10.09.2010 – 16.09.2010

Posted in astronomical time on September 10, 2010 by espacelab

Eid celebrations in Trafalgar Square in London

September 10 is Eid-Ul-Fitr
The Eid occurs at the end of Ramadan when Muslims celebrate the end of fasting and thank Allah for His help with their month-long act of self-control. Eid ul-Fitr (Arabic: عيد الفطر ‘Īdu l-Fiṭr‎), often abbreviated to Eid, is a three-day Muslim holiday that marks the end of Ramadan, the Islamic holy month of fasting (sawm). Eid is an Arabic word meaning “festivity”, while Fiṭr means “conclusion of the fast”; and so the holiday celebrates the conclusion of the thirty days of dawn-to-sunset fasting during the entire month of Ramadan. The first day of Eid, therefore, falls on the first day of the month Shawwal.

It is said that the sacred knowledge was revealed to Muhammad during the month of Ramadan. As a mark of respect to Allah and to show gratitude to him for the true knowledge that he gifted to his sons and daughters, the prophet asked his followers (and therefore the followers of Islam) to pass the month of Ramadan in fasting, prayers and other austerities and end the month-long non-indulgence with festive celebrations. This is how Eid-Ul-Fitr was born. This three-day long celebration ends the ninth month and begins the tenth month of Shawwal with absolute happiness and contentment for the ability to sacrifice for Allah. The aim of this festival is to promote peace, strengthen the feeling of brotherhood and bring oneself back to the normal course of life after a month-long period of self-denial and religious devotion.

Muslims are not only celebrating the end of fasting, but thanking Allah for the help and strength that he gave them throughout the previous month to help them practise self-control.

The festival begins when the first sight of the new moon is seen in the sky. Muslims in most countries rely on news of an official sighting, rather than looking at the sky themselves.

The celebratory atmosphere is increased by everyone wearing best or new clothes, and decorating their homes. There are special services out of doors and in Mosques, processions through the streets, and of course, a special celebratory meal – eaten during daytime, the first daytime meal Muslims will have had in a month. Eid is also a time of forgiveness, and making amends.

Solar spectacular

This week NASA’s Solar Dynamics Observatory watched as an active region in the Sun’s southern hemisphere produced a whole series of looping arcs of plasma in profile (Sept. 11-13, 2010). The arcs are actually charged particles spiraling along magnetic field lines. The images were taken in extreme ultraviolet light and reveal the dynamic activity visible above active regions. The material seen here is ionized iron heated to about one million degrees.

Black Holes
The X-ray star called Cygnus X-1 in the part of the sky where you can see Cygnus the Swan, is a black hole.

As far as we know, the first person to suggest that there were ‘dark stars’ that are impossible to see, was an English parson living in the eighteenth-century called John Michell. While rector of a parish in Yorkshire he published a number of extraordinary astronomical papers.

In 1783 Michell’s friend Henry Cavendish read one of his papers to the Royal Society that said that “If there should really exist in nature any bodies whose density is not less than the Sun, and whose diameters are more than 500 times the Sun, since their light could not arrive at us we could have no information from sight; yet, if any other luminiferous bodies should happen to revolve around them we might still perhaps from the motions of these revolving bodies infer the existence of the central ones”. These dark stars are the kind of black holes that are associated with what are called quasi-stellar radio sources, or ‘quasars’ for short.

John Wheeler was responsible for giving black holes their modern name in 1967, just after the discovery of ‘pulsars’, but it was Karl Schwarzschild who predicted their existence in 1916. Albert Einstein studied the idea and developed a mathematical description of black holes in the 1930’s. At the end of the 1930’s, Robert Oppenheimer and George Volkhoff pointed out that the equations that say neutron stars exist also put an upper limit to the amount of mass a neutron star can have, at about three times the mass of our Sun. Any bigger than this and a collapsing star would shrink down indefinitely towards a single point. This single point is called a ‘singularity’.

A collapsing object of this type would disappear to become a dark star because the gravitational pull at its surface is so immense that light itself is unable to escape into space as radiation. This brings us back to Cygnus X-1 and how astronomers pinpointed its radio signals in the 1970’s using a satellite called Uhuru. When Cygnus X-1 was identified by astronomers studying this source of X-rays using optical telescopes, it became clear that the X-rays were coming not from a blue star called HDE 226868, but from a point nearby. The star and the X-ray source orbit around each other once every 5.6 days. The mass of the object in orbit around the visible star has been calculated at 20 times the mass of the Sun, which means that if it was an ordinary star it would be bright enough to be visible, and too big to be a white dwarf or neutron star, so it must be a black hole!

There are a few more dead and dying stars like this that have been discovered recently. They are called ‘stellar mass black holes’ because they have masses similar to stars.

Our summer almanac 03.09.2010 – 09.09.2010

Posted in astronomical time on September 3, 2010 by espacelab

September 4 is the beginning of the Jain festival of Paryushana
The most important Jain festival, it consists of eight (Swetambara) or ten (Digambara) days of intensive fasting and repentance. Paryushan means, literally, “abiding” or “coming together”. It is also a time when the laity take on vows of study and fasting with a spiritual intensity similar to temporary monasticism. A time of reflection, Paryusana comes at the time when the wandering monks take up temporary residence for four months of the monsoon. In popular terminology, this stay is termed chaturmasa because the rainy season is regarded to be about four months.

Jainism is an ancient religion of India that prescribes a path of non-violence towards all living beings. In all, there are approximately 35,000 Jains living in Britain, and there are temples and community centres all over the UK – several in London, and centres in Leicester, Birmingham, Manchester, Leeds and where the community does not have a base, they hire a local school or community hall to celebrate.

This converted congregational chapel is now a Jain Centre in Oxford

Mahavira, or “Great Hero”, traditionally 599 – 527 BCE, is the name most commonly used to refer to the Indian sage Vardhamana (Sanskrit: वर्धमान “increasing”) who established what are today considered to be the central tenets of Jainism.

Asteroids pass the Earth

This week, according to NASA, two asteroids, several meters in diameter and in unrelated orbits, will pass within the moon’s distance of Earth on Wednesday, Sept. 8.

Both asteroids should be observable near closest approach to Earth with moderate-sized amateur telescopes. Neither of these objects has a chance of hitting Earth.

Heavy Stuff
At this time of year the constellation Cygnus the Swan is still clearly visible in the night sky before midnight. There is a star in this part of the sky called Cygnus X-1, an X-ray star where some very strange things are happening.

The story of its discovery begins with the search for neutron stars. In the story of our Universe that we call the Timeline section, we looked at Type II Supernovae explosions in Astrofact 26. We were interested in the way this explosive death of a star produces the everyday stuff that we are made of. As Carl Sagan used to say “we are star stuff”.

Neutron stars are what is left behind after the explosive end of huge bright stars. Neutron stars are made from the collapsing material of these huge dying stars. This material is mostly made of neutrons and is matter compacted to an extreme density. Imagine a star like our Sun with all its matter compressed like a neutron star, it could turn out to be an object less than 6 miles across. A cubic centimetre of a neutron star would weigh about 100 million tonnes.

It was in the 1930’s, just after physicists had discovered neutrons, that astronomers wondered about the possibility of the existence of neutron stars. In 1934, the astronomers Walter Baade and Fritz Zwicky thought that the only way to explain the energy output of a supernova was through the collapse of an ordinary star into a neutron star. It was only in the 1960’s with the discovery of ‘pulsars’, stars that produce rapid blips of noise on radio telescopes, that astronomers realized that they may have found rapidly spinning neutron stars.

It was in 1937 that Grote Reber, an amateur astronomer in the United States built the first radio telescope. A radio telescope detects radio waves from space, signals emitted from stars, galaxies, nebulae and other astronomical objects. In 1967 a team of radio astronomers at the University of Cambridge had built a new kind of radio telescope to look at flickering in the radio output of quasars, a term that stands for quasi-stellar radio sources. What they found were pulsars. A thousand pulsars have been found so far. Pulsars are neutron stars spinning incredibly fast with the slowest spinning round about once every 4 seconds, and the fastest turning on its axis 600 times a second. The radio noise, or signal they send out into space and is received on Earth by radio telescopes, is produced by their incredibly powerful magnetic fields, 1000 million times as strong as the magnetic field of the Earth.

The proof of the existence of neutron stars meant that another, even stranger idea would have to be explored, the possibility of ‘black holes’.