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Meteors

Giorgio Carboni, December 2009
Translated by Sarah Pogue

 


CONTENTS

 


INTRODUCTION

With the term “meteor” we are used to referring to falling stars, but this term can also have a broader meaning, such as events which occur in the sky, and we will speak about meteors in this article.  There are times in which we feel closed into our corner, we feel suffocated and we would like to have a change of air. The skies and space, for their vastness, are well-suited to travel. Here are some occasions to “travel” in air and space. It deals with simple experiences, some of which are particularly relaxing, which at the same time allow the mind to wander far away. Some experiences that I propose are easily arranged, others are a little more demanding, but I believe that all are interesting.


AEROPLANES

In the period between Spring and Autumn, the climate permits us to stretch out on a camp bed and watch the sky. Especially in the Summer, it is necessary to seek out a tree which protects us from the sunlight with its shadow. The stretched out position is very relaxing because many muscles which are normally engaged in keeping us in an upright position can now relax and rest. In fact, as soon as we lie down, we feel a sensation of rest and tranquillity. At this point you can also fall asleep, caressed by a gentle breeze. If, instead, you do not feel sleepy given your lying-down position, you can dedicate yourselves to what happens in the sky. In particular, you can observe the aeroplanes which pass. For this purpose, you will need to take with you a table on which to put a soft drink or some water and a pair of 8x30 binoculars. Now wait for the passage of an aeroplane to observe (Figure 2). While waiting, wear a pair of sunglasses to protect your eyes from the elevated brightness of the sky and clouds. When the aeroplane arrives, try to recognise the insignia of the airline company, the model of the plane and in certain cases you can even make out the passengers that look out of the windows.

Figure 2 – An aeroplane that is preparing to land, photographed with a simple digital compact camera.

Do a sketch of the visible sky tracing the profile of the vegetation and other objects which obstruct it. On this map trace the trajectory of the aeroplanes and note the hour in which they passed. Procure a timetable of the arrivals and departures at the nearest airport. With the aid of this information you can try to establish the route of the aircraft passing in the sky.

 

The best days for these observations are those in which the sky is clear. However, if there are some clouds, between one aeroplane and another, you can observe and even photograph these clouds which at times can assume really stunning shapes. It is curious to note how the clouds change form imperceptibly and at the same time rapidly.

If you want to photograph the Sun behind the clouds use an intense filter, otherwise use the reflection of a water surface such as a small garden pond or a basin of water. In this way, the light from the sun will be attenuated. Sunlight, even when only reflected, tends to damage the sensors of digital cameras, so take only a few photographs at a time and only when the sunlight is attenuated by a cloud. If you wish to take many photos, equip your camera with adequate filters.

Figure 3 – The Sun through the clouds.

Yesterday there were leaves very high in the sky, at perhaps 300 metres, then the wind calmed and the leaves fell to the ground. At times it is possible to observe even birds of prey as they are engaged in the hunt and in battles with other birds. It is not rare, for example, for hawks to be chased away by crows. You see that these birds are not very appetising for the hawks! Swallows are often visible, but they move very quickly. Some fly so high that it is difficult to distinguish them. Who knows what they do up there! In Autumn, you can observe the migration of ducks and numerous other birds. At sunset, you can admire the colours and the lights of this fascinating time of the day. You can also take photographs to use as the subjects for painting pictures.


ARTIFICIAL SATELLITES

By now night has fallen and you have had dinner. You lie down on the camp bed and while the last glimmers of sunset disperse, the stars begin to shine shine ever more numerous. It is possible to recognise the planets because, differently to the stars, they do not sparkle but their light reaches you in a constant manner. While you observe the constellations, you will see a bright point similar to a star which moves quickly between the constellations. Use the binoculars and you will see that bright point that runs between the stars: it is an artificial satellite. Suddenly it disappears: it has entered into the shadow of the Earth.

My first encounter with artificial satellites was many years ago, while I was in an open-air cinema. In a moment of boredom I began watching the stars and I saw one which moved at great speed in the heavens. It took a few days before I understood what it was. In that period, the first artificial satellites began to populate the night sky. Today, there are many more and it is easier to see them. With a powerful telescope, it is possible to see the shape of the biggest, such as the international space station (ISS), the space shuttles and some stages of the missiles launched into orbit.

But how can one know which satellite it is? On the internet there are sites dedicated to artificial satellites such as Heavens Above, http://www.heavens-above.com . Registering with one of these sites and entering the terrestrial coordinates of your point of observation, you can know the trajectory that the satellites follow that same night as they cross the sky above you. Sites such as this are able to supply you with a sky chart where the trajectory of the satellite between the constellations is indicated (Figure 4). It is possible to obtain a detail of the sky chart in a position chosen by you, therefore you can exploit this possibility to know the exact moment that the satellite will pass by a constellation or a star that you have noted and that you know how to find easily (Figure 5). The more detailed charts report the position of the satellite every few seconds. You can also obtain terrestrial charts (Ground Track) which indicate the same path but against the Earth’s surface. Furthermore, you can get other information such as the name of the satellite, its principal functions, its distance from the Earth etc. The other evening, the site indicated the next passage of a satellite at 22:37. It was to pass by a wing of the Swan constellation, Lacerta and Cassiopeia to then skim Perseus. This information revealed itself to be very important in understanding which path the satellite would have followed in the real sky. It is also possible to observe the so-called Iridium Flare, flashes of light due to the reflection of solar rays from the antennae of the Iridium satellites. These are such bright reflections that they can even be seen by day.
 

Figure 4 – Trajectory of a satellite on the vault of heaven.
(From: http://www.heavens-above.com/ )

 Figure 5 – Enlarged portion of a sky chart to show
more precisely the passage of a satellite
(From: http://www.heavens-above.com/ )

If you want to observe artificial satellites, register yourselves on the site indicated above. Be careful to enter the local time and your coordinates correctly. Then practice using the site in order to master the programs. When you are expert enough, you can surprise your friends, preannouncing the arrival of a satellite in a certain zone of the sky and within a few minutes. Therefore, prepare your observations and print the necessary maps. Prepare also an electric torch that gives a red light to observe the charts in the darkness while allowing the eyes to remain used to the dark. Go to a place which is void of bright lights and which has an ample portion of visible sky. Looking at the sky chart (Figure 4) and the constellations, try to understand which path the next satellite will follow across the sky and with an enlarged portion of the chart (Figure 5), make a date!

Materials:
8x30 binoculars;
sky chart with the trajectory of the satellite and the moment of its passing near to a known star;
electric torch with red filter;
light pollution filter made of black card to protect from light sources;
a precisely timed watch.

You can prepare the evening in such a way as to be able to observe the passage of numerous satellites. Go out at dark a half an hour before the passage of the first satellite so that you can allow your eyes to become accustomed to the dark. Go to the darkest place possible, but with the view of the sky free of obstacles. While waiting for the arrival of the first satellite, identify its path in the sky by looking at the constellations that it will pass. Artificial satellites are better seen a few hours after sunset and before sunrise. During the middle hours of the night, they pass across the shadow of the Earth and remain invisible for the best part of their trajectory.

The best evenings for this type of observation are those on which the sky is clear and void of neighbouring lights. On these evenings, the stars appear very bright on the dark background. The presence of haze, light clouds and the moon worsen the visibility of the stars and of the artificial satellites. On the other hand, you can observe our natural satellite “run” amongst the clouds. This is a fantastic spectacle, which is worth photographing or, even better, filming.

http://en.wikipedia.org/wiki/Satellite History of artificial satellites and many other information.
http://www.heavens-above.com Study this site well because it gives important information including a description of all the constellations and the positions of the asteroids and the more visible comets.

Terms for internet searches: satellite tracking


FALLING STARS

While you wait for the arrival of an artificial satellite, you can also pay attention to falling stars, known to astronomers as meteors, that silently trace their bright trail in the sky. Meteors are fragments of composition similar to that of the rocky planets, such as the Earth. Their formation dates back to approximately 5 billion years ago, during the birth of the solar system. They are differentiated into carbonaceous, metallic (iron-nickel), stony and mixed meteors. Upon their entrance into the atmosphere they travel at an incredible speed of between 11.2 and 72.8 km/s. On contact with the upper layers of the atmosphere (at approx. 80 km), before the falling object the air is strongly compressed, the meteors overheat and become extremely bright while they lose mass through fragmentation, liquefaction and combustion. In general, the meteors are very small and they extinguish themselves long before they touch the ground. The part which touches the ground is called a meteorite. Every day, millions of meteors enter the Earth’s atmosphere. On average, in your portion of sky you should see about ten every hour, but in certain periods of the year they are much more frequent. In fact, meteors often travel in so-called "swarms". These swarms take their name from the constellation from which they seem to come. The Perseids swarm is famous, visible between the end of July and the beginning of August. The origin of the meteoric swarms is associated with the passage of comets through the Earth’s orbit. Due to the disintegration of these celestial bodies because of the effect of sunlight, the comets leave a trail of particles behind them, in general only a few millimetres in size. When the Earth, in movement around the sun, crosses one of these trails, many of these particles enter the atmosphere at high speed and they ignite. For many swarms, astronomers know the comet from which they derive. For example, the Perseids are associated with the Swift-Tuttle comet.

 

For their observation, procure a sky chart on which you should identify the radiant of the swarm which you wish to observe. Take an electric torch equipped with a red filter in order not to unaccustom the eyes to the darkness. This is all you need to carry out these observations. The best moment is generally during the second half of the night, when the Earth encounters the meteoric fragments. Obviously, it would be better to go to a location devoid of lights. The meteors are more frequent and more visible on the side of the earth that is turned forward with respect to the direction of progress of our planet, therefore in the second half of the night. If you want to take photographs, bring a tripod and a camera with which it is possibile to have manual exposure. Try keeping the iris open at about f = 2 with an exposure of 5 minutes. In these photos, you will see the stars complete a circular arc around the axis of the Earth’s rotation, while the meteors appear to come from a single point or radiant.

Figure 6 - (From:
http://bizarrelabs.com/met.htm )

One morning in August of 1993 (?), I got up early for work. For the previous night advance notice had been given of an intense swarm, I think the Perseids swarm, which did not appear. That morning, instead, at dawn I saw a meteor shower. There were so many that I was afraid of being hit. They didn’t give off any light, but I saw them arrive to Earth because of the smoky trail that they let fall and that the air deformed rapidly. Their speed was about 10m/s and falling they didn’t cause any damage. I witnessed this phenomenon for at least a half an hour. When I left the car in a carpark and I went to the station to catch the train, those meteors were still falling on the city. It was a striking spectacle, but not at all reassuring. I thought that they were relatively small and therefore had been much slowed down by the atmosphere. Given the trail of smoke that they left behind, they must have been rich in carbon. If I had seen them at night, they would probably also have left a bright trail. I would like to see a photo of that dawn.

On sale, you can find astronomical texts which also report data regarding the principal meteoric swarms, such as the following:
Patrick Moore - The Guinness Book of Astronomy, 1995, ISBN 085112643X
http://en.wikipedia.org/wiki/Meteor_shower A description of the meteor swarms
http://en.wikipedia.org/wiki/List_of_meteor_showers  The list of the principal meteor showers

Terms for internet searches: list meteoric swarms, meteor showers


ASTEROIDS

Asteroids and comets also formed with the solar system. As you know, after the big bang, in space there were only hydrogen and helium. It was in the stars that all the remaining chemical elements were formed. Approximately 5 billion years ago, in the neighbourhood of the future solar system, a supernova exploded disseminating in the surrounding space an immense quantity of chemical elements. These in turn combined to form compounds. These dusts mixed with the hydrogen and helium still present in space and from their principal condensates the Sun and the different planets formed. When the nuclear furnace of the Sun began to produce light, it pushed the remaining dusts away and within a few million years, the aggregation phase of the celestial bodies was complete.

If we remove the sun, the planets and their satellites, in the solar system numerous celestial bodies still remain. They are the asteroids and the comets. The asteroids formed within the orbit of Jupiter, but the comets beyond this orbit. The asteroids have a mass of over 107 kg and a diameter less than that of a planet, but they do not usually have a spherical form. The asteroids are found above all in the “principal asteroid belt", a zone that lies between the orbit of Mars and Jupiter. The so-called NEO (Near Earth Objects) are important for our safety. These are objects whose orbits can intersect that of the Earth. Astronomers keep an eye on them, but they have not yet taken a census of all of them. The bigger ones of 1 km number from 500 to 1000, but in general asteroids are much smaller.

Many amateurs have discovered new asteroids, but the undertaking is not easy due to the ever more fierce competition and the automatic discovery systems of which various astronomical observatories dispose. It involves, however, taking two photographs of a certain zone of the night sky with a telescope at a distance of one hour and comparing them to see if the object has moved with respect to the stars in the background. In the positive case, it is necessary to determine the position of the object in order to communicate it to the Minor Planet Center. To operate in this field, it is necessary to have a reflecting telescope with an aperture of at least 200 mm, a CCD sensor for astronomy, a robust tripod equipped with an electronic pointing and pursuit system. Finally, it is necessary to have an observation point which is as free as possible from light pollution. With this article I limit myself to proposing simpler observations, such as those of falling stars, but whoever wishes to interest themselves in these unnerving objects will have to turn to a group of amateur astronomers linked to an astronomical observatory to have all of the information and tips necessary.

http://www.solarviews.com/eng/asteroid.htm An introduction to the asteroids.
http://nssdc.gsfc.nasa.gov/planetary/planets/asteroidpage.html Information from Nasa
http://www.heavens-above.com This site indicates the position of the more visible asteroids.

Terms for internet searches: asteroid discovery, asteroid search, asteroid tracking, deep space surveillance.


COMETS

As I have said, comets are also a residual from the formation of the solar system, but while the asteroids formed within Jupiter’s orbit, where the light of our star was stronger and caused the evaporation of the ice that those celestial bodies possessed, the comets formed in a position further away where the light of the sun was weaker and could not cause the evaporation of the ice present in their interior. The comets are found principally in the Oort cloud, which envelops the entire solar system and is situated between approximately 20,000 and 100,000 UA, or between 0.3 and 1.6 light years from the sun. Therefore, at the boundary with the nearest stars, which are located at a distance of approximately 4 light years. In this cloud there are thousands of billions of comets. When the position of one of these is disturbed by another celestial body, the comet can begin a long journey towards the sun. Another reservoir of comets is the Kuiper belt, a flattened ring which extends beyond the orbit of Neptune for 50 UA (one Astronomical Unit is equal to the distance between the Earth and the sun). The majority of the comets that come to visit us are periodic, that is, they pass around the sun in a periodic manner. These have a closed orbit, of an elliptical form, and one focus of their orbits is the sun. The long period comets (with a period of more than 200 years and as much as several million years) come from the Oort cloud, while the short period comets (with a period of less than 200 years) come from the Kuiper belt.

The observation of visible comets with the naked eye is an occasional activity since between the passage of one visible comet and another many years can pass. If the comets are very bright, their observation is very simple because their presence in the night sky is evident. If, howerver, the comets are not very bright (the vast majority), it is necessary to know their position with celestial coordinates, or at least the constellation. As in the case of the observation of the meteoric swarms, bring a sky chart and an electric torch fitted with a red filter. To observe the less bright comets, it is necessary to use a pair of binoculars or a telescope with a low magnification, wide field of view and a good aperture. When the comets are very close and bright, they are a real spectacle. Particularly if you observe them from a dark place on a night when the sky is clear, you will see the colours of the tail(s).

Some comets come to us for the first time and so a race begins to sight them first and to give them their name. Since the comets can also be of considerable size, they can pose a threat to the Earth. The discovery of new comets is an important activity and numerous amateurs dedicate themselves to this work, and of course many professional astronomers who have telescopes with a large aperture and other important equipment. In this field, the American astronomer Carolyn J.S. Shoemaker is famous for the number of celestial objects that she has discovered: 32 comets and more than 800 asteroids up to 2002. In spite of the limited performance of their instruments, amateur astronomers are responsible for the majority of comet discoveries. In order to dedicate yourself to this activity you need only a pair of binoculars for astronomy which are reasonably bright (lens diameter 80-100 mm) and with a low-medium magnification (10-20 X). Binoculars for astronomy must be suitable for lengthy observations, therefore they must be equipped with an attachment for a tripod and furthermore, to avoid contortions and a subsequent stiff neck, they must have eyepieces inclined at 45° or better at 90°. If you are an early riser and you normally get up at dawn, then you are made to be a comet hunter (... rather than grunbling around the house at 5 in the morning!). If this subject peaks your interest, inquire with a group of astrophiles linked to an astronomical observatory to have all the necessary information.

http://en.wikipedia.org/wiki/Comet General description of comets.
http://www.heavens-above.com This site indicates the position of the more visible comets.
http://nineplanets.org/kboc.html The Kuiper Belt and The Oort Cloud.
http://astronomyonline.org/SolarSystem/AsteroidIntroduction.asp Asteroids and comets, an introduction.

Terms for internet searches: comet discovery, comet search, comet sighting.
In the astronomy magazines, you can find all the necessary information for observing meteoric swarms, comets and other celestial phenomena of the present month.


CONCLUSION

It is not always possibile to keep up with the tasks of which our life is made. Every so often it is necessary to take a break and think of something different, something pleasant, maybe also something enlightening. With this article, I have given you some ideas to allow your imagination to run amongst the clouds and even further! If you are looking for something that makes you useful, help the astronomers to identify potentially dangerous asteroids and comets.

 

VISUAL CHARACTERISTICS OF SOME CELESTIAL OBJECTS

 

Sparkling bright point, fixed with respect to the stars.

star

Non-sparkling bright point (except on windy nights). From one day to another it moves with respect to the stars.

planet

Bright point which moves with respect to the stars. Sometimes it flashes due to the reflection of light from the sun. In a couple of minutes it crosses the sky.

artificial satellite

At night intermittent coloured lights.

aeroplane

A bright body that ploughs through a good portion of the sky in an instant.

falling star

Body visible only with an instrument with a good aperture. It moves with respect to the surrounding stars. 2 photos taken at a distance of one hour are necessary to reveal its movement.

asteroid

More or less diffuse light/glimmer, with a brighter nucleus and possibly an evanescent tail (which can be very long)

comet

 


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