Our summer almanac 02.07.2010 – 08.07.2010



Polaris is the most important star for finding the cardinal directions of east, west, north and south, as it remains in a fixed position in the night sky above the North Pole.

The only deep sky object in this constellation is the Ursa Minor Dwarf dwarf elliptical galaxy. It was discovered by A.G. Wilson of the Lowell Observatory in 1954. It is part of the Ursa Minor constellation, and a satellite galaxy to the Milky Way. The galaxy consists mainly of older stars and there appears to be little to no ongoing star formation in the Ursa Minor Dwarf galaxy.

The Planck mission
Nearly 13 months ago on the 5 June 2009 the ESA’s Planck satellite carried out a critical mid-course manoeuvre that will placed the satellite on its final trajectory for arrival at L2, the second Lagrange point of the Sun-Earth system, early in July.

The Lagrange points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects such as a satellite and where it is positioned in relation to the Earth and Moon. The Lagrange points mark positions where the combined gravitational pull of the two large masses provides precisely the right kind of centripetal force required to rotate with them, so they allow an object to be in a “fixed” position in space rather than move around in an orbit in which its relative position is constantly changing.

The Sun–Earth L2 is a good spot for space-based observatories, because an object around L2 will maintain the same orientation with respect to the Sun and Earth’s night time side of the planets surface, and so shielding and calibration of these delicate instruments are much simpler. This position is still far away from Earth so solar radiation is not completely blocked by the shadow of the Earth.

Planck cruising to L2
Credits: ESA – D. Ducros

The manoeuvre was scheduled to begin at 19:28 CEST on 5 June 2009, and lasted up to 30 hours.

Coolest spacecraft ever in orbit around L2
On 3 July 2009 the detectors of Planck’s High Frequency Instrument reached their amazingly low operational temperature of -273.05°C, making them the coldest known objects in space. The spacecraft has also just entered its final orbit around the second Lagrange point of the Sun-Earth system, L2.

Planck is equipped with a passive cooling system that brings its temperature down to about -230°C by radiating heat into space. Three active coolers take over from there, and bring the temperature down further to an amazing low of -273.05°C, only 0.1°C above absolute zero – the coldest temperature theoretically possible in our Universe.

Such low temperatures are necessary for Planck’s detectors to study the Cosmic Microwave Background (CMB), the first light released by the universe only 380 000 yrs after the Big Bang, by measuring its temperature across the sky.

All sky image

This week on 5 July 2010, the Planck mission delivered its first all-sky image. It not only provides new insight into the way stars and galaxies form but also tells us how the Universe itself came to life after the Big Bang.

“This is the moment that Planck was conceived for,” says ESA Director of Science and Robotic Exploration, David Southwood. “We’re not giving the answer. We are opening the door to an Eldorado where scientists can seek the nuggets that will lead to deeper understanding of how our Universe came to be and how it works now. The image itself and its remarkable quality is a tribute to the engineers who built and have operated Planck. Now the scientific harvest must begin.”

From the closest portions of the Milky Way to the furthest reaches of space and time, the new all-sky Planck image is an extraordinary treasure chest of new data for astronomers.

The main disc of our Galaxy runs across the centre of the image. Immediately striking are the streamers of cold dust reaching above and below the Milky Way. This galactic web is where new stars are being formed, and Planck has found many locations where individual stars are edging toward birth or just beginning their cycle of development.

Less spectacular but perhaps more intriguing is the mottled backdrop at the top and bottom. This is the ‘cosmic microwave background radiation’ (CMBR). It is the oldest light in the Universe, the remains of the fireball out of which our Universe sprang into existence 13.7 billion years ago.

While the Milky Way shows us what the local Universe looks like now, those microwaves show us what the Universe looked like close to its time of creation, before there were stars or galaxies. Here we come to the heart of Planck’s mission to decode what happened in that primordial Universe from the pattern of the mottled backdrop.

The microwave pattern is the cosmic blueprint from which today’s clusters and superclusters of galaxies were built. The different colours represent minute differences in the temperature and density of matter across the sky. Somehow these small irregularities evolved into denser regions that became the galaxies of today.

A Clockwork Universe
The picture of the universe we have now is avery different one from the early days of modern science, when clocks and clockwork were one of the leading technologies. The Clockwork Universe Theory was a theory, established by Isaac Newton, as to the origins of the universe in this. age when clocks were an important technology in an age when machines would soon create a new industrial world.

A “clockwork universe” can be thought of as being a clock wound up by God and ticking along, as a perfect machine, with its gears governed by the laws of physics. What sets this theory apart from others is the idea that God’s only contribution to the universe was to set everything in motion, and from there the laws of science took hold and have governed every sequence of events since that time.

This idea was very popular among deists during the Enlightenment, when scientists realized that Newton’s laws of motion, including the law of universal gravitation, could explain the behavior of the solar system.

However Newton excludes the idea of free will from this world of mechanical motions, since if people believed that all things have already been set in motion and are just parts of a predictable machine, then, Newton feared, the idea of everything being predetermined would lead people to not believing in a God any more.

Isaac Newton’s conception of the universe was one huge, regulated and uniform machine that operated according to natural laws in absolute time, space, and motion. In this new world that Newton created, God was the master-builder, who created the perfect machine and let it run. God was the Prime Mover, who brought into being the world in its lawfulness, regularity, and beauty. This view of God as the creator, who stood aside from his work and didn’t get involved directly with humanity was called Deism and was accepted by many who supported the “new philosophy”.

A similar concept goes back, at least, to John of Sacrobosco‘s early 13th century introduction to astronomy: On the Sphere. Johannes de Sacrobosco or Sacro Bosco (John of Holywood, c. 1195 – c. 1256 AD) was a scholar, monk, and astronomer (probably English, but possibly Irish or Scottish} who taught at the University of Paris and wrote the authoritative mediaeval astronomy text Tractatus de Sphaera.

Sacrobosco spoke of the universe as the machina mundi, the machine of the world, suggesting that the reported eclipse of the Sun at the crucifixion of Jesus was a disturbance of the order of that machine.

These days we can see that this theory was very much an idea of those times. Modern physics undermines this theory with the second law of thermodynamics ( the total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value) and quantum physics with its unpredictable random behavior.

Orrery
An orrery is a mechanical device that illustrates the relative positions and motions of the planets and moons in the solar system in a heliocentric model. They are typically driven by a clockwork mechanism with a globe representing the Sun at the centre, and with a planet at the end of each of the arms.

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