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decorative picture for the mainstream pages Observation arrow back picture and link to the theoretical tutorials A Observation Session

Any observation session may only begin once the telescope you will used correctly set. That concerns a practicle and comfortable installation for the observer as well as the settings of a equatorial mount, for example. Then comes the question of looking for the celestial object(s) one wants to observe. You will note that all the operations as described hereunder assume that you will respect the characteristics and operations proper to any telescope and mount used as such data, among others, are found in the user's manual for the telescope and mount. As such that can void, about such or such point -or for the whole- the following. Of note too that the time dedicated to the preparation of a observation must not alter, in terms of time, to the observation proper and that that preparation phase has to be done swiftly and methodically

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How ro Ready a Observation
Telescope and Mount General Settings
Setting A Equatorial Mount
Vision Dark Adaptation
Searching A Celestial Object Through a Telescope's Visor
Searching a Celestial Object Through its Coordinates

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It is usually adviced that a observation session be prepared

A balcony may afford for a observation post. Here with a typical -albeit ancient somewhat- 114/900 Newtonian telescope!A balcony may afford for a observation post. Here with a typical -albeit ancient somewhat- 114/900 Newtonian telescope! site 'Amateur Astronomy'

arrow back Telescope and Mount General Settings

Before any observation session, a astronomical instrument has to be balanced on the mount (note: those developments concern the equatorial mounts only; as far as altazimuthal or even modern automatized mounts, please check your telescope's instructions of use). Balancing a telescope on its mount is about to optimize the work of the equatorial mount and to avoid any premature wear through unbalanced force. It is best to balance a telescope like it will be used during the observation session, with no cover, a ocular in the ocular holder or any other accessory (like features for astrophotography, etc.). About counterweights generally, make sure that the blocking screw is really present and screwed (that screw is taken off to have the counterweight placed upon the axis). Thus any wrong action will not lead to that some -heavy- counterweight falls upon your toes! As far as balancing the declination axis is concerned, you will have first the occasion to check wheter the telescope's tube is on its axis indeed as some shift might be due, for example, for some telescopes, to that the fin declination flexible has been used during a previous observing session. Just re-align the tube correctly. As far as the declination balance proper is concerned, first lock the right ascension (R.A.) axis (in its simpliest position is the best); then unscrew slightly -or any other system- the telescope's tube related to its berth or mount so to allow it to move along. That must not have it too however to slide when you do not hold it anymore! Just unlock the R.A. axis now and balance your telescope through moving it on the berth -or any other form of support. Whatever the position about the declination axis, the telescope should remain stable when you release it from your holding. Once you find that balance, just lock the declination axis. As far as the R.A. axis' balance is concerned, now, that balance is attained through the use of that axis' counterweight(s). First, lock the declination axis (in its simpliest position the better, which is about perpendicular to the R.A. axis). Move counterweight(s) to their average position. Unlock the R.A. axis and find a balance, for any position about that axis, through a fail-and-try process which consists into moving counterweight(s) either side of the average position. Take note that, should you add -or remove- any additional accessory to the telescope during the observing session, you will have to entirely re-do the balance process

Now, you may procede with the visor settings. Note that the followings are concerning optical, and not red-point visors. To tune a visor, you'll need first a distant object (which may, or not, be lighted function of the time at which the settings are done). Setting a visor is done with a low-magnification ocular in the ocular-holder. Just aim the telescope's tube to the object through a fail-and-try process and have it at the center of the ocular. Then lock both the telescope's axis and using the visor's support system -which often is a three-screw one- just have that same object at the center -most ofen reticulated threads- of the visor. Just check now that the process on the visor did not move the object in the telescope's ocular. You may renew the process with larger magnification oculars, especially if your observation session is about feeble, deep sky objects. for more detailed instructions about how to tun a classical three-screw telescope's visor, check our tutorial How to Tune a Classical Three-screw Telescope's Visor?

At least a half-hour before the beginning of the observation session, you will have, should you observe with a open-tube telescope like a Newtonian, or a Dobsonian, etc., to allow the telescope to adapt thermally to the environment. The temperature and the air status in the telescope's tube will have to turn homogeneous with that of the surroundings. Generally that is made by opening the tube's cover, as more advanced systems, for example, recently have appeared, like fans to speed cooling and blow out mixed-temperature air. Otherwise, a 10" Newtonian may take 2-3 hours to stabilise!

arrow back Setting A Equatorial Mount

That part of that tutorial doesn't concern automated mounts the settings of which is more and more computerized. Setting a astronomical telescope's equatorial mount consists into correctly tuning the latter. The principle of how a equatorial mount is working is that the main axis of it turns, for all planes, into parallel to the Earth's axis. Setting a equatorial mount thus consists into making such that alignment. It is better to have the settings done once the night set as you may have to use the Polaris. A simple setting is possible, on a other hand, when the observation session will be mostly made visually. Advanced settings are needed for any astrophotography work, which may assume some manual or motorized, accurate, or long-duration following of a object, or to search a celestial object by the mean of its celestial coordinates. Setting a equatorial mount must be done for each observation session, some aspects excepted in the case, for example, of a permanent pier or observatory, etc.

arrow back Vision Dark Adaptation

Dark adaptation is the key to any astronomical observation. That is due to that the eye, in a dark location, is adapting with the pupils getting larger as the retina gets adapted. After about between 30 minute and one hour, retina will have reached its maximal adaptation. A well-adapted eye, under dark sky conditions, is able to reach down to a magnitude above the 6th, which is considered the limit of what can be seen naked-eye. Once the dark adaptation en cours or attained, the observer must not expose himself back to any source of light because that would have the adaptation terminated. Hence amateur astronomers are using feeble red-light lamps for example. Some sources, recently, quote that such a lamp should be green-lighted as they say that the eye is few sensitive to red. Your 'directing eye' is the term used to tell what eye you preferably use to observe with a astronomical telescope (or to aim with a shooting gun, for example). For a right-handed person, that usually is the right eye, and conversely. In terms of astronomy, your directing eye is often more apt to see small details and it is more sensitive in the dark. Another concept which is useful in amateur astronomy is that of 'peripheral vision.' Retina, that image captor located at the rear of your eye indeed is working by the mean of two types of cells, the cones and the batonnets. Cones are allowing daytime, or artificial light colored vision as the batonnets, which are very sensitive, are allowing nighttime, or penumbral vision (vision in those conditions however does not catch colors). Batonnets are found mostly on the periphery of the axis of vision. The peripheral vision thus consists, for deep sky objects mostly, into shifting the point which your eye is aiming to! That brings to that the celestial object is then activating the batonnets instead of the cones. To do that, when the object observed is centered in the telescope's ocular, direct your eye to one side, or the other, of the field -or even the black area around. That is just improving the vision of that object. During a observation session, generally, on a other hand, let's recall that the object observed had to lie at the center of the ocular as you will have your eye lying at a few millimeters away from the ocular's lens, which is where the image of the object if forming. Let's recall too that eyeware bearers will have to take if off to focus the telescope ocular holder as the telescope's optics will compensate for the eye default. That is not true for astigmatism for which the eyeware is to be kept during observation, for low-magnification oculars mostly as is should be possible to take if off at high magnification. At last, do not forget that deep sky objects are deceiving at first sight, and especially if you refer to medias' spectacular deep sky pictures. Such objects, furthermore, won't display one, or some colors only when they are luminous enough. Others will remain grey. Colors of deep sky objects generally need telescopes with a aperture of at least 16". From a more detailed point of view, one may know too that dark adaptation brings a increase of the eye's focal length and a decrease of the eye's accomodation faculty, which are termed 'nighttime myopia' and 'nighttime presbytia,' respectively. Of interest too are that eye's cones sensitive to blue compared to those sensitive to green and red, are much less performant as, by night, the eye's maximal sensibility is in the blue (as by daytime, it is in the green-yellow). Note too that should you have expose yourself to strongly lighted landscapes before a observing session, like a beach, a snow field, or a sunny day, etc., during a long period of time, your eye will have lost about 3/4 of a magnitude in terms of night vision. The eye theoretically need more than 24 horus to reach again its optimal dark adaptation ability

arrow back Searching A Celestial Object Through a Telescope's Visor

Starhopping from alpha Tri down to M33, the Triangle GalaxyStarhopping from a Tri down to M33, the Triangle Galaxy. site 'Amateur Astronomy'

Searching a celestial object, generally, with a database-featured automatized telescope (or a 'go to telescope') is easy because the telescope is automatically aimed to that object! For telescopes which are manually set, we will here share between looking for a bright celestial object, and looking for a faint, deep sky one

arrow back Searching a Celestial Object Through its Coordinates

Searching a celestial object through its coordinates consists into aiming a telescope mounted upon a non-automatized equatorial mount to a celestial object through the use of the coordinates of that object on the celestial sphere! That is done using both graduated circles of the mount, a one associated to the right ascension (R.A.) axis (which allows the telescope to rotate in a opposite direction, and with the same speed, to the Earth's rotation about itself), and the other to the declination axis (which allows the telescope to move in a northern or southern direction). The R.A. circle may be turned relative to the R.A. axis as the declination axis may not. Such that technique long was described like mostly useful to the daytime observation of Venus, so to be able to observe that planet before it reaches a too important brightness, or to the search of a daytime Venus-bright star closeness. Recently, and despite the apparition of automatized mount, that technique now is also described like allowing to find deep sky objects or any celestial object by night more easily than through the telescope's visor. Sources describe the nighttime technique nowadays like using a landmark-star which is allowing to 'link' the telescope's R.A. axis with the celestial sphere as the daytime technique may also be used for a nighttime observation

A equatorial mount's graduated declination circleA equatorial mount's graduated declination circle. site 'Amateur Astronomy'

Website Manager: G. Guichard, site 'Amateur Astronomy,' http://stars5.6te.net. Page Editor: G. Guichard. last edited: 4/17/2012. contact us at ggwebsites@outlook.com
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