The Experience At The Zero

Part One

By Caecilia Triastuti  Djiwandono

What is meridian and what is the Prime Meridian?

Knowing the position of where we are on earth helps us to realize our being.  Hence the knowledge of our location relatives to other things on earth is an important start-point to build our sense of orientation about ourselves in this universe. Astronomers have created the concept of latitude and longitude, both are measured in degrees- minutes -seconds, in which the two variables will bring us to one unique point on earth. In order to measure how far north or south we are, people have come up with something called latitude and how far east or west we are as longitude. An imaginary line has been determined as the fixed reference to start the measurement, as the 0º.  For latitude, the 0º imaginary line is drawn along the Equator. For the longitude, the 0º imaginary line is from the top to the bottom of the Earth, which is called the Prime Meridian. Do you know where the location of the Prime Meridian is?

When you go to London , United Kingdom , and visit the Royal Observatory in Greenwich , you will see the Prime Meridian. The Royal Observatory, Greenwich (ROG) is the home of Greenwich Mean Time (GMT) and the Prime Meridian of the world.  The imaginary line becomes the real one, as in picture 1, which you can see represents the Prime Meridian of the world -  Longitude 0º. Every place on Earth is measured in terms of how many degrees east or west from this line. Notice that along the line, names of big cities and capital cities in the world are stated on the line with each the number of its longitude, either eastern or western site of the line, including our capital city Jakarta . Therefore the line divides the Earth into western and eastern hemispheres, just like the Equator divides it to southern and northern hemispheres.  That is why we can say the ROG is one of the centres of world time and space. Its importance makes it considered as one of the most important historic scientific sites in the world. The Observatory, which is part of National Maritime Museum , is one of the most famous features of Maritime Greenwich that since 1997 it has become a UNESCO World Heritage Site.

The historical background of the Observatory

The Royal Observatory, in Greenwich , was built in 1675 by King Charles II in the King’s land Royal Park that is far above the River Thames, London . The land where the observatory was built is a hill in Greenwich Park , on the site of Greenwich castle.  King Charles II ordered Christopher Wren, then a prominent British astronomer- cum- architect. The castle originally belonged to Duke Humphrey, who was the Duke of Gloucester. The castle was often used as a guest house and hunting cottage by King Henry VIII.  King Charles recognized the need for an observatory that could help determine the longitude of places on the Earth. During the 17^th century, sailors at sea had problems in finding their longitude, that is, how far east or west they were due to the absence of “landmarks” in the middle of the wide ocean.  This lack of knowledge resulted in many ships getting lost, or getting into an accident and sinking, or running out of supplies.  Scientist suggested that sailors would know their longitude by observing the position of the stars and the Moon. In doing so, they would need to know where the stars and the Moon would be at different times of the month. In order to improve navigation at sea, King Charles established the observatory. This activity involved the accurate measurement of time, for which the observatory became famous for in the 19^th century.

The establishment of the Prime Meridian

In 1884 the Prime Meridian was marked by the position of the large “transit circle” telescope in the Observatory’s Meridian Building . It was Sir George Biddell Airy, the 7^th Astronomer Royal, who built the transit circle in 1850. The cross-hairs in the eyepiece of the Transit Circle accurately defined longitude 0° for the world. Hence this prime line of meridian is not a natural entity, but determined by convention. Since the late 19th century, this Prime Meridian has been used as the reference line for Greenwich Mean Time (GMT or UT, Universal Time). The immense development of transportation and communication networks during 1850s and 1860s in the world makes the need for an international time standard as something inevitable. As the earth’s crust is moving subtlety all the time due to its rotation on its axis, the exact position of the Prime Meridian is moving very slightly too from time to time. But the world keeps the Airy Transit Circle in the Royal Observatory, Greenwich as the original reference for the prime meridian of the world. *** (to be continued)

Atacama Large Millimeter/submillimeter Array: In search of our Cosmic Origins

By: Diah Y.A. Setia Gunawan

The astronomy world has studied extensively the electromagnetic radiation emitted by objects in the universe at almost all wavelengths, from the high energy X-ray radiations to the very long waves in the radio range. However, the realm of the light from some of the coldest and most distant objects in the universe are still not well explored. These objects radiate light that has wavelengths of around a millimetre, which is between infra-red light and radio waves and is heavily absorbed by the water vapour in the Earth's atmosphere. So far, technology had only allowed limited observations of this light region, which involved very time-limited and expensive space telescopes or low-resolution and low-sensitivity earth-based telescopes, giving us patchy  and crude overview of the origin of the universe.

However, we are now entering a new millimetre and sub-millimetre era. The world's leading astronomy institutions are joining efforts in building a revolutionary observatory: the Atacama Large Millimeter/submillimeter Array (ALMA). High in the thin and dry air of the Chilean Atacama desert, with an array of up to 66 high-precision state-of-the- art antennas, the ALMA will search for the cosmic origins by observing cold, distant objects at millimetre and sub-millimetre wavelengths.

As water droplets heavily absorb and  scatter the signals of millimetre and sub-millimetre wavelength, humid air would degrade the quality of informations received from the already weak signals of the cold objects. The Chajnantor plateau of the Chilean Atacama desert offers both dryness (annual rainfall below 100mm), and high altitude (5000 metres). The unique combination of dryness and high altitude that the Atacama desert offers means that the atmosphere above it contains the least water droplets on earth surface. With the wide and flat plateau of Chajnantor and the very cooperative acceptance of Chile to host world astronomy makes the location the best site on earth for the spread of the array (up to 16 km distance between two farthest antenna -baseline) of ALMA.

The 12-m diameter antennas will be used for interferometry, a technique where each antenna can pair with every other antennas to observe an object. When the data from each pair of antennas are combined, the resulting image can be as sharp as that of a single telescope with a diameter equivalent to the longest baseline in the interferometer. The antennas will be movable which allows reconfigurable baselines, allowing 'zooming' action. The compact configuration will give high sensitivity, wide field view, while the extended configuration allows a high angular resolution. ALMA will operate at 0.3 to 9.6 millimetres, or 30 GHz to 1 THz, which will be divided into ten frequency bands, giving high spectral resolution.

With this unprecedented combination, ALMA will be the tool for studying objects from the very young universe, which are now seen at great distances of billions of light years, with their light mostly stretched out due to the expansion of the universe (red shifted) to the millimetre and sub-millimetre wavelengths. ALMA will also study the processes of star and planet formation, as ALMA will penetrate the surrounding dust that obscures the visual observations. Further more, ALMA will study in detail giant clouds of gas and dust around stars and in planetary systems, map gas and dust in the Milky Way and other galaxies, investigate stellar sizes, determined the chemical composition of the dust surround stars, study the Sun and origin of solar wind.

When it is ready, expected to be in 2012, ALMA will open up a new wavelength range to us and help us understand our Cosmic Origin and give us a better understanding of the Universe. ***

Link Alma: www.alamobservatory.org

ALMA ARRAY This image shows an artist conception of the Alma array with roads, in the extended configuration. (C) ESO

Amazing Universe

By: Iman Santosa

 Look up in the clear night sky and you will see thousands of twinkling stars. There are also four planets that we can see with the naked eye, the moon (not every night), and if we are lucky there are some shooting stars as well. All those heavenly bodies seem to move around the Earth. That’s why our ancestors believed that Earth lay at the centre of the universe. Today, we know that it was not true. But the question is still there: where is our place in the universe?

 Let us try to figure out how big the universe is. As we know our planet is the member of the family of the Sun, called the Solar System. Planet Earth sits in the third spot in a line of eight planets (Pluto is not a planet any more) with the Sun at the center of Solar System. The distance from the Earth to the Sun is 150 million kilometers. If we reduce that distance to 1 meter then the distance between Neptune (the eighth planet) and the Sun will be 30 meters. The nearest star beyond Solar System is Alpha Centaury, which is more than 250 kilometers away. Because the distance between one star to another star is so huge, astronomers use light years instead of ordinary unit. One light year is the distance that light travels in a year. Alpha Centaury is four light years from us. So light takes 4 years to travel from our planet to Alpha Centaury. This is an enormous distance comparing 8 minutes from the Sun to the Earth. It takes only 1,3 second for light to travel to the moon while Apollo missions took 3 or 4 days to get there. How many millions of years would it take for Apollo to go to Alpha Centaury ?

 Our Solar System, Alpha Centaury, and all other stars we see in the night sky, and more than 200 billion stars that we can not see, are in our Milky Way galaxy. The Milky Way galaxy, is a spiral galaxy that stretches 100 thousand light years from side to side. In this galactic scale, the Solar System is merely a small dot in the Orion Arm, located about two-thirds from the centre of the galaxy. Obviously, four light years to Alpha Centaury is a very short distance.

The nearest galaxy is Andromeda which is 2,5 millions light years from us. Andromeda is also a spiral galaxy and its size is slightly larger than our galaxy. Another big galaxy around the Milky Way is the Triangulum Spiral. There are also some smaller galaxies in the neighborhood. Our Milky Way, Andromeda and 40 smaller galaxies are in the small gathering called the Local Group. Its size is 3 million light years across. The Local Group is part of a supercluster galaxy called Virgo Supercluster that contains thousands of galaxies. Our Local Group is some 60 millions light years from the centre. Now, imagine there are millions of superclusters in the universe!

Back to the simple question we asked earlier, the answer is not easy. The universe is simply too big. The Hubble Space Telescope can observe galaxies as far as 10 billions light years away. But it may not be the edge of the universe. If we can not answer one simple question it doesn’t mean that our effort to explore the universe is useless. In the world of science the question is more important than the answer. In fact, it is this intense curiosity which leads to questions which drive the human civilization. For the universe is full of mystery, there are lots of questions challenging astronomers to think and work harder. Every single discovery reveals an amazing universe and at the same time raises another question. And that makes astronomy  a very challenging science. It has fascinated people thousands of years ago and will fascinate people a thousand years more. ***