Selecting An Observing Site; Choosing The Best Time To Observe; Cooling The Telescope; Adapting Your Eyes - Celestron Astromaster LT 60AZ Mode D'emploi

SELECTING AN OBSERVING SITE

If you are going to be observing deep-sky objects, such as galaxies and nebulae, you should consider traveling to a dark
sky site that is reasonably accessible It should be away from city lights, a relatively unobstructed view of the horizon, and
upwind of any major source of air pollution Always choose as high an elevation as possible as this can lower the effects of
atmospheric instability and can ensure that you are above any ground fog While it can be desirable to take your telescope
to a dark sky site, it is not always necessary If you plan to view the planets, the Moon or even some of the brighter deep-
sky objects, you can do this from any location, such as your own backyard Try to setup the scope in a location that is out
of the direct path of streetlights or house lights to help protect your night vision Try to avoid observing anything that lies
within 5 to 10 degrees over the roof of a building Rooftops absorb heat during the day and radiate this heat out at night
This can cause a layer of turbulent air directly over the building that can degrade your image It is best if you set your
telescope up directly on a dirt or grassy surface Setting up on any raised platform such as a wooden deck or a hard surface
like concrete or a sidewalk should be avoided as they transmit vibrations easily that can be transferred to the telescope
Observing through a window is not recommended because the window glass will distort images considerably And an open
window can be even worse, because warmer indoor air will escape out the window, causing turbulence which also affects
images Astronomy is an outdoor activity

CHOOSING THE BEST TIME TO OBSERVE

Try not to view immediately after sunset After the sun goes down, the Earth is still cooling, causing air turbulence As the
night goes on, not only will seeing improve, but air pollution and ground lights will often diminish Some of the best observing
time is often in the early morning hours before dawn Objects are best observed as they cross the meridian, the imaginary
line that runs from north to south through a point directly over your head This is the point at which objects reach their highest
points in the sky and your telescope is looking through the least amount of atmosphere possible Objects that are rising or
setting near the horizon will suffer more atmospheric turbulence since you are looking through a much longer column of air
It is not always necessary to have cloud-free skies if you are looking at planets or the moon Often broken cloud conditions
provide excellent seeing

COOLING THE TELESCOPE

Telescopes require at least 10 minutes to cool down to outside air temperature This may take longer if there is a big
difference between the temperature of the telescope and the outside air This minimizes heat wave distortion inside the
telescope tube (tube currents)

ADAPTING YOUR EYES

If you are planning to observe deep sky objects at a dark sky site, it is best if you allow your eyes to fully adapt to the dark
by avoiding exposure to white light sources such as flashlights, car headlights, streetlights, etc It will take your pupils about
30 minutes to expand to their maximum diameter and build up the levels of optical pigments to help your eyes see the faint
light from a distant target If you need light to help setup your telescope in the dark, try using a red LED flashlight at as low a
brightness setting as possible and avoid looking straight at the light source This will give you the best chance of capturing
those faint deep sky objects
When observing, it is important to observe with both eyes open This avoids eye fatigue at the eyepiece If you find this too
distracting, cover the unused eye with your hand or an eye patch The center of your eye works well in bright daylight, but is
the least sensitive part of the eye when trying to see subtle detail at low light levels When looking in the eyepiece for a faint
target, don't look directly at it Instead look toward the edge of the field of view and the object will appear brighter
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