Terrestrial Viewing, Astronomical Observation

For example, the GoScope has a focal length of 350mm, which when used with the supplied 20mm eyepiece yields:

amateur astronomy. The following information and observing tips will help you get started.

350mm

20mm

= 17.5x

Choosing an Observing Site

When selecting a location for observing, get as far away as

The magnification provided by the 10mm eyepiece is:

possible from direct artificial light such as street lights, porch

350mm

10mm

= 35x

lights, and automobile headlights. The glare from these lights will greatly impair your dark-adapted night vision. Set up on a grass or dirt surface, not asphalt, because asphalt radiates

The maximum attainable magnification for a telescope is directly related to how much light it can gather. The larger the aperture, the more magnification is possible. In general a fig- ure of 2x per millimeter of aperture is the maximum attainable for most telescopes. Your GoScope has an aperture of 70 mil- limeters, so the maximum magnification would be about 140x. This level of magnification assumes you have ideal conditions for viewing.

Keep in mind that as you increase magnification, the bright- ness of the object viewed will decrease; this is an inherent principle of the laws of physics and cannot be avoided. If mag- nification is doubled, an image appears four times dimmer. If magnification is tripled, image brightness is reduced by a factor of nine!

Start by centering the object you wish to see in the 20mm eyepiece. Then you may want to increase the magnification to get a closer view. If the object is off-center (i.e., it is near the edge of the field of view) you will lose it when you increase magnification, since the field of view will be narrower with the higher-powered eyepiece.

To change eyepieces, first loosen the securing thumbscrew on the diagonal. Then carefully lift the eyepiece out of the holder. Do not tug or pull the eyepiece to the side, as this will knock the telescope off its target. Replace the eyepiece with the new one by sliding it gently into the holder. Re-tighten the thumbscrew, and refocus for your new magnification.

Terrestrial Viewing

Most users will use their GoScope extensively for viewing ter- restrial (Earth-based) objects during daylight hours. It excels for viewing birds, wildlife, sporting events, vistas, or anything else you want to see close-up.

Remember to aim well clear of the Sun, unless the front of the telescope is fitted with a professionally made solar filter (available from Orion). Otherwise, permanent eye damage could result. Children should use the GoScope only with adult supervision.

Astronomical Observation

The GoScope also is a good telescope for casual stargazing. It can show much more than what is visible on Earth during the day. Once the Sun sets, there are literally thousands of objects in the night sky that can be inspected more closely. For many, this will be the first foray into the exciting world of

heat which disturbs the surrounding air and degrades the images seen through the telescope. Avoid viewing over roof- tops and chimneys, as they often have warm air currents ris- ing from them. Similarly, avoid observing from indoors through an open (or closed) window, because the temperature differ- ence between the indoor and outdoor air will cause image blurring and distortion.

If at all possible, escape the light-polluted city sky and head for darker country skies. You’ll be amazed at how many more stars and deep-sky objects are visible in a dark sky!

“Seeing” and Transparency

Atmospheric conditions vary significantly from night to night. “Seeing” refers to the steadiness of the Earth’s atmosphere at a given time. In conditions of poor seeing, atmospheric turbulence causes objects viewed through the telescope to “boil”. If you look up at the sky with your eyes, and the stars are twinkling noticeably, then the seeing is bad and you will be limited to viewing with low magnifications. Planetary and Moon observing may also be poor.

In conditions of good seeing, star twinkling is minimal and images appear steady in the eyepiece. Seeing is best over- head, worst at the horizon. Also, seeing generally gets better after midnight, when much of the heat absorbed by the Earth during the day has radiated off into space.

Especially important for observing faint objects is good “transparency” – air free of moisture, smoke, and dust. All tend to scatter light, which reduces an object’s brightness. Transparency is judged by the magnitude (brightness) of the faintest stars you can see with the unaided eye (6th magni- tude or fainter is desirable).

Cooling the Telescope

All optical instruments need time to reach “thermal equilibri- um.” The bigger the instrument and the larger the temperature change, the more time is needed. For optimal performance, allow at least 30 minutes for your telescope to cool to the tem- perature outdoors.

Let Your Eyes Dark-Adapt

Don’t expect to go from a lighted house into the darkness of the outdoors at night and immediately see faint nebulas, gal- axies, and star clusters—or even many stars, for that matter. Your eyes take about 30 minutes to reach perhaps 80% of their full dark-adapted sensitivity. As your eyes become dark- adapted, more stars will glimmer into view and you’ll be able to see fainter details in objects you view in your telescope.