Observation 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

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

How ro Ready a Observation

It is usually adviced that a observation session be prepared

• first, one obviously will have to check for the weather of that night before getting into the preparation (that can also be done through such weather services like the NOAA)
• then, mostly, data are to be collected about the observation planned like the meridian for a planet, the Great Red Spot longitude, etc. for example for a planetary observation. Or a photocopy from a celestial atlas, or a print from a astronomical software, etc. for the field observed in case of the observation of deep sky objects. Some of such data, on the other hand, may already be copied upon the observation report gabarit (check our tutorial "How to Record A Observation")
• by sunset, when observation will take place in the first part of night, you will too take note of how the sky is looking, especially any hint that the weather could change once the observation session started like elevated clouds, etc.
• few before the beginning of the session, at last and before entering the following operations, you will gather all the accessories necessary like the oculars, other accessories, astrophotography tools (the good working of it you will possibly have checked), laptop computer, observation record gabarit (or sketchbook), drawing support, drawing pen(s), pen(s), etc. Of course, a red-hued lamp avoiding dazzling too, a reliable time-measuring tool (mostly our watch correctly check against any reliable time system, a softwre included)
• of note too that you should worry about being comfortable. Comfortable in terms of temperature, clothing and footwear should you observe during a cold -or even fresh- night. Comfortable in terms of general setting, like a seat, for example, a outdoor table, etc. And in terms of comfort generally speaking (with hot drinks, snacks, etc.) which may be of importance for long observation sessions, like for a Moon eclipse, for example. A comfortable and stable seating further, generally, is improving -psychologically?- your vision. Some think that a noisy environment has to be avoided too because observation is a intellectual activity which is linked to the nervous system and that your eye's retina is also part of the latter

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

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!

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.

• in any case, first begin by setting your telescope's tripod the most horizontally possible, which may also be done with a level tool
• for a simple setting process, first you will have to align the right ascension (R.A.) axis towards North. That can be determined with a map, a compass or, more simply, with the Polaris, that star which lies about dead North. You then have to adjust the inclination of the R.A. axis to have it really pointing towards the Polaris. That is done by adjusting the inclination by a value equal to that of the latitude of the observer's location
• for a advanced setting process, the previous one has to be improved for a largest accuracy of the alignment. How the process is easy or not depends upon what settings or accessories are available on your equatorial mount, like, for example, a polar visor or simple and accurate devices to set the mount's azimuth, or its inclination, or the latitude's angle. Basics are to use both the telescope and the visor. Once a simple setting done like above, you will have to aim the telescope, through the mount settings, so that the Polaris is seen at the center of a low-magnification ocular (like a power of 45x). That necessitates that you will have correctly set the telescope's visor. First set the value of the declination axis' graduated circle unto the one of the Polaris' declination, which is 89° and 16'. That is done whatever the value of the R.A. graduated circle. Once done just lock the declination axis. Then, through the sole settings of the equatorial mount in terms of azimuth and inclination, just bring the Polaris to the telescope's visor's center. That done, center now the Polaris into the ocular used, with that same mount's settings. That setting may be improved through using larger-magnification oculars. Once the Polaris definitively centered, lock the azimuth and inclination settings and, here your are! Your telescope is ready for the observation session. The tube motions then will be performed through the main move locks, or the fine-motion flexibles of both the R.A., and the declination axis only

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

Searching A Celestial Object Through a Telescope's Visor

Starhopping 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

• aiming to a bright celestial object (a bright star or a planet, for example) unfolds like the following. As the visor will have set parallel to the telescope's tube, and featured with a crosshaired reticule, that fact that you will bring the objet at that reticule in the visor will have it also at the center of the ocular. To do that, you will use a low-magnification ocular and through the telescope's mount -a altazimuthal, or a equatorial one- you will use both appropriate axis, with a amplitude allowed by the mount, using the visor to aim to the object observed. For equatorial mounts which allow both large motions and a fine tuning through flexibles on both axis, one brings grossly the object in the visor's field through large motions as fine-tuning motions are used to bring it to the reticule. The celestial object then is lying at the ocular's center. Red-dot visors necessitate a technique which we do not expose here
• aiming to a faint, dark sky celestial object (lie a faint star or a nebula, etc.) is more complicated due to that the object, most usually, is not visually seen in the visor. The technique is then to look for the nearest visible object in the visor, to the one you search. Once found, you then will 'star hop' to the faint object! That technique comes into variations function of their authors as it can be termed with varied names as the English-speaking amateur astronomers mostly term that 'star hopping.' Star hopping necessitates that you will have done some preparative work ahead of your observation session, or to at least have some celestial atlas or a laptop with a astronomical software at hand. The better however looks like to have prepared a simple, easy-to-use chart from a atlas or a celestial software. That chart will schematize the star hopping path you will use from the bright, to the faint object you want to observe. The starhopping will be different according to whether your telescope will be set upon a altazimuthal, or a equatorial mount. Just think for both that any telescope will bring some inversion of sort compared to that chart and that, when you will draw that chart, you will be presented the choice to orient it in a classical, celestial atlas way, with celestial North to the top, or in a astronomical software way, with the celestial North at a angle to the vertical function of the observer's location. The second display is more appropriate to a altazimuthal mount as the chart will then show you more easily the azimuthal-vertical motions needed. Any of those chart displays is either appropriate to a equatorial mount. A other aspect to take in account as far the making of a starhopping chart is concerned, is the ease of what motions you will have to perform with the mount to reach the celestial object you are aiming to. It's easier, with a equatorial mount, to used starhopping legs which are parallel to the right ascension circles, and declination lines. With a altazimuthal mount, it will be easier to device starhopping legs as parallel, or perpendicular to the horizon! In both situations, you'll maybe want to use the way -which is the one we procede with- with consists into privileging straight legs. Even if, by the end of a move (as seen in the ocular) reckoning stars are not lying by the ocular's center (but are visible anyway), it will suffice to re-center those before proceding to the next leg! At least, and maybe above all, you will have had to check the dimensions of the field of the ocular used. That is relatively easy to do. Just place in the ocular's field a seemingly easily identifiable field of stars, like a bright star and its surroundings for example and just measure the ocular's field by reference to a celestial atlas or a astronomical software. Should you want to observe a relatively bright deep sky object, one might use a ocular which will yield a large field of view enough albeit allowing the sight of the object at the same time. Now, we will take like a example of starhopping the search of the M33, or the Triangle Galaxy which we will search through a telescope which inverts the field from North to South, used atop a equatorial mount, and with a starhopping chart oriented to the North celestial pole. That search will be done with a ocular yielding a " field of view and a power of 45x. Our starhopping itinerary is leaving from the 3.4th magnitude star a Tri. Should that star already too faint to see with the visor, like in a suburban sky, you should have to draw a starhopping chart to that star, starting at Hamal, in Aries, the Ram, for example, which could complicate the process. First, search a Tri in the visor and center it into your ocular. Following the right ascension (R.A.) circles, you will from a ocular's field of view to the other, reach the first landmark star, that of the 8.3th magnitude. Just re-center it to the center of the ocular's field, now just hop to the next, 7.5th magnitude star. And so forth! When reaching the 8.3th star at the lower right, you will just follow, that time, towards the celestial North, a straight leg along the declination lines. That will easily bring you to M33!

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 circle. site 'Amateur Astronomy'

• both techniques first need that the telescope be set in terms of balance, orienting the mount, etc., according to the advanced setting process
• the search of a celestial object through the coordinates nighttime technique is the easiest. It necessitates mostly that you aim the telescope to a bright object which is close enough to the object you want to find. You will also need a non-dazzling red-lighted lamp to be used to procede with the setting of the graduated circles of the mount. We will take like a example the search of M33, or the Triangle Galaxy. The next bright object is Mirach, a 2nd magnitude star in the constellation Andromeda, Andromeda. First, you will write down, from a celestial atlas or a astronomical software, the equatorial coordinates of both the searched object, M33, and the landmark star, Mirach. Equatorial coordinates are the one in relation with the celestial sphere and expressed in right ascension (R.A.) or the equivalent of longitude on Earth, and in declination, or the equivalent of latitude. R.A. is counted in hours, minutes, seconds as declination is in degrees, minutes and seconds of arc. Mirach's coordinates are like R.A. 1h 09m 43.9s, dec. 35° 37' 14.0", which can be simplified like R.A. 1h 09mn, dec. 35° 37'. M33's coordinates are simplified alike into R.A. 1h 33mn, dec. 30° 39'. As you will have set your telescope with a advanced settings process, you now will first search for the landmark-star through its coordinates. First unlock both axis of the mount and grossly aim the telescope to that star and then lock both axis. After that, unlock the declination axis only and set the declination value of Mirach unto the graduated declination circle, with is 35° 37' and lock that axis back. Unlock then the mount's R.A. axis and you will bring Mirach to the reticulated center of the telescope's visor. Because you will have set the declination value of Mirach on the declination axis, the motion in R.A. necessarily brings that star into the visor as the mount's R.A. axis now is turning around the celestial pole -the pole of the celestial sphere- at a fixed distance, the one of the declination you set! That centering is refined within a low-magnification ocular. Once done, you have just to turn the mount's graduated R.A. circle -a one which is mobile relative to the axis- unto the R.A. value of Mirach, which is 1h 09mn. That first part of the process has just brought to that the telescope's mount now is anchored somehow to the celestial sphere with both the mount's declination and the R.A. circles referring to the same references than the equatorial coordinates system of the celestial sphere. As you will now swiftly set upon both the mount's circles the R.A. and declination values for M33, the object we want to observe will stand in the ocular as your telescope will read those values upon the celestial sphere, in accordance with the coordinates system of it. Simply! That is easily done by successively unlocking and locking back both the R.A. and declination axis of the telescope's mount, setting 1h 34mn and 30° 39' like the values respectively. Should you plan to observe several objects during a same observing session, the best will be, by intervals, to re-do those operations with any other landmark-star. Also check then that any fine motion of the declination axis through the axis flexible will not have shift the alignment of the telescope tube to the axis. Reset the alignment through the flexible if needed
• the search of a celestial object through the coordinates daytime technique needs to use the concepts of hour angle and sidereal time. That technique also allows to directly set the right ascension (R.A.) value of the object without the need of any landmark-star, which may also be used for a nighttime observation. The concept of 'hour angle' allows to know the position in the observer's sky of a given object which is identified through its coordinates in the equatorial coordinates system of the celestial sphere, for the given day and time of the observation, which is possible due to that the celestial sphere is turning about the celesetial pole. Stars are identified upon the celestial sphere through the equatorial coordinates system, which allow to locate any star through a right ascension (R.A.) and declination value, or the equivalent of the longitude and latitude, respectively, for a object on the Earth. That equatorial coordinates system is a one which is independent of any consideration of date and time as it just refers to the 'vernal point,' a point where the ecliptic crosses the celestial equator up and the origin of the R.A. and to the celestial equator which is the projection of the Earth's equator unto the celestial sphere. That has like a consequence that the vernal point, or the origin of the R.A. values, due to the rotation of the Earth about itself, is rotating altogether with the celestial sphere. It rotates with a period of 23 hours and 56 minutes, as that period determines the hour angle. To get the hour angle of a given celestial object, one has thus to know what the sidereal time is for the day and time of the observation session. That is done either through a dedicated astronomical freeware or, more simply, through a astronomical sky charts one which usually also gives the sidereal time. The hour angle may also usually be given by such a software. As far as the daytime or nighttime search of a object for observation, you will first have to determine what is the object's hour angle which is giving a value to be set unto the mount's right ascension (R.A.) graduated circle. Let's take like a example the search of M33 again, the Triangle Galaxy! M33 has like -simplified- coordinates a R.A. of 1h 33mn and a declination of 30° 39'. The R.A. value is termed 'alpha.' Should we want to observe M33 on October 17th, 2012 by 10:30 p.m. local time since the city of Dijon, France. Any astronomical sky chart software (in which you will have set the observatory for that city) will give you the sidereal time, or 'T.' Which with our example if 23:16. The hour angle, or 'H,' for M33 is also given, like 21:41, which can also be computed like a result of H = T - alpha. That hour angle value, 21h 41, is thus set unto the mount's R.A. circle along with M33's declination, which is 30° 39' set unto the declination circle as M33, the Triangle Galaxy should now lie at the center of the telescope's ocular!