Orion SPACEPROBE 130ST EQ Manuel d'utilisateur télécharger pdf (Page 14)

D. The Stars

Stars will appear like twinkling points of light. Even power-

ful telescopes cannot magnify stars to appear as more

than a point of light. You can, however, enjoy the different

colors of the stars and locate many pretty double and mul-

tiple stars. The famous “Double-Double” in the constellation

Lyra and the gorgeous two-color double star Albireo in

Cygnus are favorites. Defocusing a star slightly can help

bring out its color.

E. Deep-Sky Objects

Under dark skies, you can observe a wealth of fascinating

deep-sky objects, including gaseous nebulas, open and

globular star clusters, and a variety of different types of gal-

axies. Most deep-sky objects are very faint, so it is important

that you find an observing site well away from light pollution.

Take plenty of time to let your eyes adjust to the darkness.

Do not expect these subjects to appear like the photographs

you see in books and magazines; most will look like dim gray

smudges. Our eyes are not sensitive enough to see color in

deep-sky objects except in a few of the brightest ones. But

as you become more experienced and your observing skills

get sharper, you will be able to ferret out more and more

subtle details and structure.

How to Find Deep-Sky Objects: Star Hopping

Star hopping, as it is called by astronomers, is perhaps the

simplest way to hunt down deep-sky objects to view in the

night sky. It entails first pointing the telescope at a bright star

close to the object you wish to observe, and then progress-

ing to other stars closer and closer to the object until it is in

the field of view of the eyepiece. It is a very intuitive tech-

nique that has been employed for hundreds of years by pro-

fessional and amateur astronomers alike. Keep in mind, as

with any new task, that star hopping may seem challenging

at first, but will become easier over time and with practice.

To star hop, only a minimal amount of additional equipment

is necessary. A star chart or atlas that shows stars to at least

magnitude 5 is required. Select one that shows the positions

of many deep-sky objects, so you will have a lot of options

to choose from. If you do not know the positions of the con-

stellations in the night sky, you will need a planisphere to

identify them.

Start by choosing bright objects to view. The brightness of

an object is measured by its visual magnitude; the brighter

an object, the lower its magnitude. Choose an object with

a visual magnitude of 9 or lower. Many beginners start with

the Messier objects, which represent some of the best and

brightest deep-sky objects, first catalogued about 200 years

ago by the French astronomer Charles Messier.

Determine in which constellation the object lies. Now, find the

constellation in the sky. If you do not recognize the constella-

tions on sight, consult a planisphere. The planisphere gives

an all-sky view and shows which constellations are visible on

a given night at a given time.

Now, look at your star chart and find the brightest star in the

constellation that is near the object you are trying to find.

Using the finder scope, point the telescope at this star and

center it on the crosshairs. Next, look again at the star chart

and find another suitably bright star near the bright star cur-

rently centered in the finder. Keep in mind that the field of

view of the finder scope is about 7°, so you should choose

another star that is no more that 7° from the first star, if pos-

sible. Move the telescope slightly, until the telescope is cen-

tered on the new star.

Continue using stars as guideposts in this way until you are

at the approximate position of the object you are trying to

find (Figure 13). Look in the telescope’s eyepiece, and the

object should be somewhere within the field of view. If it’s

not, sweep the telescope carefully around the immediate

vicinity until the object is found.

If you have trouble finding the object, start the star hop again

from the brightest star near the object you wish to view. This

time, be sure the stars indicated on the star chart are in fact

the stars you are centering in the eyepiece. Remember, the

finder scope (and main telescope eyepiece, for that matter)

gives an inverted image, so you must keep this in mind when

star hopping from star to star.

8. Care and Maintenance

If you give your telescope reasonable care, it will last a

lifetime. Store it in a clean, dry, dust-free place, safe from

rapid changes in temperature and humidity. Do not store the

Figure 13. Star hopping is a good way to locate hard-to-find

objects. Refer to a star chart to map a route to the object that uses

bright stars as guideposts. Center the first star you’ve chosen

in the finder scope and telescope eyepiece (1). Now move the

scope carefully in the direction of the next bright star (2), until it

is centered. Repeat (3 and 4). The last hop (5) should place the

desired object in the eyepiece.

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Orion SPACEPROBE 130ST EQ Manuel d'utilisateur Page 14

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