The Big Dipper is a constellation that is familiar to most people, and is visible all year long, thus it should be a good starting point to learn the night skies. By using the map below, and few simple methods of pointing your telescope, this page will demonstrate the basics of celestial navigation. The green concentric rings located in the centre of the constellation map represents the two outer most rings on a Tel Rad viewfinder, and are offered as a scale reference. This page assumes that the reader does not have a Tel Rad and will discuss two other methods in locating the listed objects.
The first method uses straight line reckoning by way of reference stars and the naked eye. By imagining a straight line between and/or through one or more stars, you can more accurately visualize the location of a desired celestial object. You can also, if the object is appropriately located, triangulate an object's position by picturing the object as one point on an imaginary triangle. Scroll down and look at the map. The reference lines are white in colour and are useful in locating objects away from the stars of the main constellation (red lines). Once you have a visual idea where the celestial object is located in reference to the main stars of the constellation, then you can point your scope at that area and employ your viewfinder or do manual sweeps through the telescope to do the final locating.
The second method uses your telescope's setting circles to aid in locating objects. In order to employ this method you must have your scope reasonably well polar aligned, and the setting circles on your telescope must be easy to read and large enough to be accurate. Most Schmidt Cassegrains and high end equatorial mounted scopes will be accurate enough to suit your needs. One of the downfalls of even the best setting circles (electronic ones excluded) is that their accuracy deviates from one part of the sky to another. In this method you will calibrate the Right Ascension (left to right movement) setting circle to a nearby reference star of known coordinates and then move the scope until the coordinates of the desired object is displayed in both Right Ascension (RA), and Declination (Dec). Declination is the up and down setting circle of the scope and is generally not calibrated to the reference star provided it is accurately adjusted (consult your telescope's manual). If the Dec circle reads differently from the reference stars coordinate, then set this circle to match it or make not of its deviation and add or subtract this amount from the desired object's Dec. This second method is the most accurate and should get you within an eyepiece view width of the desired object. If your scope does not have a clock drive, you must move from the reference star quickly as after a few minutes the reference star will have moved relative to your scope. If you do have a clock drive, then your setting circles will maintain good calibration in relation to the reference star for as long as the clock drive is running. A word of caution, the farther you move away from this reference star, the more inaccurate your setting circles will become this is why a new reference star is used to calibrate the setting circles for each new object that is to be located.
Map generated with Earth Centred Universe
Also
known as the Whirlpool Galaxy (~35million ly distant) as the larger of two neighbouring
galaxies is pulling stars and other matter from the smaller galaxy like debris being
sucked into a whirlpool. 8" and larger scopes will reveal individual arms and a
stellar 'bridge', smaller scopes will show a pear shaped formation of galaxies in this 9.6
magnitude object. If you extend an imaginary line from Dubhe through 69 UMa.
Intersect this line with a perpendicular line drawn from Alkaid, and you will find M51
just above where these lines meet.
To use your setting circles, align your scope until Alkaid is in your low power (20-25mm)eyepiece. Now adjust your RA. circle until it reads the RA coordinate of Alkaid: RA 13:47. Your Dec. circle should read close to +49° 19', if not you may have to calibrate your Dec. circle(see your scope's owner's manual). Now move your scope in RA. and Dec. until M51's coordinates of RA. = 13:30 and Dec.= +47° 16' is displayed by each respective circle's pointer. M51 should be within the eyepiece of your scope, or it is very close. If not, consult your scopes owner's manual to ensure you are reading the circles properly, and check your polar alignment.
A
pinwheel shaped spiral galaxy (~15million ly distant) that is as large in appearance as a
full moon. Despite its large size, this object has very low surface brightness and
is surprisingly hard to find unless you are looking carefully. Fortunately M101
forms one point of a equilateral triangle with the stars Alkaid and Mizar. While you
are in the area, check out Mizar as it is a double star with its companion Alcor.
To use your setting circles, align your scope so that Alkaid is in your eyepiece. Set your circles to the coordinates for Alkaid: RA 13:47.5, and Dec. +49° 19'. Now move your scope until the coordinates for M101 (RA 14:03.3 Dec +63° 45') are displayed by the setting circles. Make sure you are under dark skies for this one as any light pollution or haze will make viewing this object impossible.
This
is a multiple star system that Messier believed to be nebulous. However no nebrosity
exists so one wonders if Messier might have been the victim of the poor optics of the
time. Easiest method is to use the setting circles. Calibrate your circles to
69 UMa: RA 12:15.4 and Dec +57° 02', then point your scope until RA 12:22.3 and Dec +58°
05' is displayed.
A
barred spiral galaxy that sits just right to the star 64 UMa. This star is very
bright so make sure it is out of the telescope's view when observing M109 as the glare
will ruin any chances of seeing any detail in this faint galaxy. This object does
not require any trickery to locate, just sweep to the left of 64 UMa.
Cigar
shaped, edge on galaxy that is suspected to be very much like our own Milky Way galaxy,
but 35 million ly. distant. Calibrate your setting circles to Merak: RA 11:01.8 and
Dec +56° 23' and then sweep your scope to the left until the circles read RA 11:11.5 and
Dec +55° 40'.
This
planetary nebula (3000 ly) was formed when a dying star threw off its outer layer in a
blinding supernova explosion. This ejectile matter of gas and dust happened to leave
a pattern that resembles an owl's face with two dark eyes. This is another object
that requires either very dark skies, or a narrow band nebula filter in order to see any
detail. If you have just been observing M108, sweep a little more to the left and
you should see this fascinating celestial object. If you have used your setting
circles to locate M108, just move the scope until RA 11:14.8 and Dec +55° 01' is
displayed by the indicators.
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These two galaxies are spectacular not only for their brightness but for their proximity to one another. If you use a medium power eyepiece (12-17mm), you will be able to view both of these galaxies at the same time. M81 is a spiral galaxy with distinctive dust lanes, while M82 is a cigar shaped edge on galaxy. Both are approximately 8 million ly from Earth. To visually locate these objects draw an imaginary line from 64UMa, continue just to the left of Dubhe, and extend it to a 4.6mag star called 24UMa. Just below and to the left of this star you will find M81 and M82.
The coordinates of 24UMa is: RA 09:34.5 and Dec +69° 50'. The coordinates for M81 is: RA 09:55.6 and Dec +69° 04'. If you are unsure of the position of 24UMa, then calibrate your setting circles to Dubhe at RA 11:03.7 and Dec +61° 45'.
This page has endeavored to demonstrate the basics of celestial navigation. While not exhaustive, this writer has neglected to demonstrate either use of the Tel Rad finder or star hopping techniques, it is hoped that the reader has gained a basic understanding. Initially it takes much longer to locate objects (it took me 3 hours to locate M81 and M82, but now I can locate it in a few minutes). As these skills are mastered the reader will become much more proficient and develop their own patterns and techniques that work best for them. The key to all of this is dark skies, and patience.
