Astronomy without danger


Elementary precautions to take at the time of the observations.

There are leisures where the danger is always present in an obvious way. That encourages the participants to take constantly the precautions which are essential. Alas, in our meetings of observation the danger is well hidden and involves sometimes very serious accidents. You reassure, the goal of this text is not to make you believe that astronomy is a highly perilous activity, or that it is necessary to be formed in a school of commandos of marine, to be able to take a stereotype of the moon. However, a long experiment of this healthy activity taught us the existence of some dangers. It is very significant to know them well to practise in full safety the observation of the sky, one of the oldest occupations of the man.

Serious dangers

Observation of the sun

An instrument for the visual observation of the remote objects (binocular, glasses, telescope...) is before a whole funnel with light. Indeed, the light which crosses its objective (much larger than our eye) is concentrated before penetrating in the eye of the observer.

If this last directs, without particular precaution, its telescope towards the sun, the intensity of the light will be such, that its eye will be plugged instantaneously and definitively. If the apparatus is powerful (diameter higher than 150mm), that will be able to even cause very quickly a boiling of the physiological liquids of the eye, involving its explosion.

The majority of the small instruments which one finds in the trade are provided with a very dark filter, marked " SUN ". the observer must place this object in front of the eyepiece at the time of the solar observations. Alas these accessories badly support the thermal shocks to which they are subjected and they often burst. These filters should never be used with instruments of more than 60mm of diameter, and even with this opening, it is impossible for us to guarantee a total security to you. As for us, we place our filters at the entry of our instruments, this avoids any dangerous concentration of light.

Thus any danger appears isolated. But at the time of the public meetings of observation of the sun, it is not rare to see curious which tries to remove the filter " to see it more closely ", whereas an observer is with the eyepiece! Or then, another unconscious will look with the researcher of the instrument, but this one is protected by a lens cap. Our individual has then the regrettable idea to withdraw this stopper...

In conclusion:
- It is necessary to be very careful at the time of the solar observations.
- It is necessary to check the good condition of the filter and its good installation.
- a stopper must cover the objective with the researcher.
- It should not be touched the instrument when somebody puts his eye at the eyepiece.
- Be wary of the behavior of the public.

Observation in full day

In full day one can observe other thing that the sun. For example, it is interesting to use binoculars to contemplate the landscape, or a telescope to seek Mercure or Venus near the solar disc. You include/understand now which is the danger. It is necessary to take care not to direct the instrument towards the sun, even a short moment!
Thus seek never Mercure or Venus of day with binoculars. It is suicidal!
If you wish to observe these planets with a telescope, this one in the shade, thus you place will be certain not to make bad meetings in the field of the eyepiece.
Pay attention to the children: Never leave your binoculars to young children without monitoring. They observe in all the azimuths by being unaware of the danger and can move towards the sun. It is not by them warning against the glare of the star of the day that you will regulate the problem. Indeed, we already saw a child who, questioning the words of his parents, voluntarily directed the binoculars towards the sun. A child knows that it will be made forgive by his family if it makes a silly thing but is unaware of that with the sun it is not entitled to the error. The sun will never forgive it.

Observations of night

After having studied the dangers due to an excess of light, see those which are due to the darkness. The risk is caused this time by the environment of the instruments. An obstacle or a hole which one would have easily avoided of day, will be invisible of night.
The ground of observation must thus be free from any dangerous obstacle like the sprinkler devices (there is in all the good lawns), the large stones, or the beams (as those which border the bowling pitches). Also take care not to leave the ground strewn with the ustensils such as bicycles, stools, cases of accessories, balls of game of bowls, etc...
Pay attention not to get to you footholds in the inevitable electric wire which feed the driving mechanism of the telescopes.
If the presence of obstacles on the ground is dangerous, their absence can be mortal in certain circumstances. Never organize public observations near a pit of shooting to the insane shooting-trap without guard, or of a well in protection, and even less close to a cliff.
The small holes can also be very dangerous (pothole, hole of golf, brook, etc...), they can cause falls. The night those are always very dangerous.

The instrument is not a balustrade

In spite of their imposing silhouette, the large telescopes of amateur are not enough stable so that one can rest on it above. The majority of the people who use them for the first time of it are not conscious. That especially involves falls which can be very impressive, if the observer were perched on a stool. This represents the principal source of accidents, sometimes serious, which can occur at the time of the public meetings of observation, in spite of the recommendations which we systematically lavish on this subject.
You never press on a telescope!

Small misfortunes

The eye with the eyepiece

When an observer directs its instrument using the researcher, it is frequent to see curious putting the eye at the eyepiece without preventing. You can then bet that this last brutally will receive the eyepiece in the eye. Indeed, the observer is not conscious of the situation and will be brought to make quickly swivel the telescope in various directions.
Thus put never the eye at the eyepiece without being invited there.
Also take care not to let trail your fingers on the instrument at the time of the operations. You could make you wedge them.


If you want to photograph the objective of an instrument with a flash, wait at least until the observer withdrew its eye of the eyepiece. If not this one will be strongly dazzled during several hours.

Automatic watering

It is of good tone to organize the observations on a lawn or in the vicinity immediate. We previously drew your attention to the danger which the nozzles of watering represent which are sometimes disseminated on the grass.
Another concern is due to the automatic operation of certain sprinkler devices. If you do not stop it front, this one will not fail to start in the medium of the meeting. What will be regrettable for the hardware and the observers.

Brittleness of the instruments

Certain large transportable telescopes of amateur require, for their startup, a minimum of athletic qualities on behalf of the user. However, as soon as the instrument is installed, one should not any more force. The telescopes and the glasses are instruments of very high precision even when they have a coarse appearance. It is thus advisable to handle them carefully.
The orientation of the instrument must be done without effort. If it is not the case, it is that you forgot to free it.
When you directed it, you can block the movements. Do it without excess. It is not necessary to force on the handles of blocking to obtain a sufficient immobilization. Note that in fact the devices of blocking generally break.

To know to live and night observation

So that it reigns a good environment at the time of the night observations, it is necessary to take care not to obstruct itself mutually.

The light

When we arrive in an obscure place, our eyes adapt. First of all our pupils dilate. This can take a few seconds. Then, the retina of the eye evolves/moves in the darkness. Its sensitivity increases gradually. It requires one hour, to reach its maximum habituation. This adaptation disappears quickly with the least dazzling. It is for that that it is necessary to proscribe the sources of sharp light. The flashlights must be filtered using a very dense filter. If you must use an intense lighting, put you at the variation of the group.
Do not use a photographic flash without to have asked for the agreement of all the participants. If not you could veil films or unpleasantly dazzle observers which had carefully adapted their sight to the darkness.
Pay attention to the lighters, light your cigarette with the variation of the group. In addition, will know that the gleam of your cigarette will be very awkward for the people who côtoient you in the darkness and for the stereotypes that you will want to carry out.


The contemplation of the sky requires a minimum of mental concentration. This one will be supported by calms and the silence of the place. Thus avoid shouting or using a radio set. Also think, if necessary, with the close dwellings in which people probably sleep.

Around the instruments

The instruments will have to be sufficiently distant from/to each other in order to prevent that the observers are not obstructed mutually. Take care not to pass in front of the instrument of the neighbor. Do not touch an instrument when it is used. The vibrations which you would cause would be amplified by the enlargement and would make the observation unpleasant.


Some of these recommendations could seem obvious to you or be made smile. However each accident or incidents to which we referred is really produced. We wish that you take our advice, in order not to renew these errors.
Observe in peace and security.