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Terrestrial and Celestial Viewing with the
StarBlast 90mm
The Orion StarBlast 90mm is equipped with a built-in, 45-degree
"correct-image" diagonal, which provides an upright, "normal"
view. Because of this, the StarBlast is an excellent terres-
trial telescope for viewing Earth-based scenes during daylight
Figure 8. The small accessory case holds the two eyepieces and the
finder scope.
hours. More powerful than binoculars, it can get you visually "up
close" to your target for vivid, detailed views. For best results,
however, DO NOT VIEW OUT WINDOWS. The glass in a win-
dow is approximately 1000 times less accurate than the optics
of your StarBlast 90mm – so it will soften your views, and things
will seem to be slightly out of focus. If you must view through
a window, use the lowest power available (and open the win-
dow!).
The StarBlast 90mm also excels for nighttime viewing, enabling
you to see hundreds of craters on the Moon, Jupiter and its four
major moons, the rings of Saturn, and much more! If you take
the telescope to a location away from city lights (the darker, the
better), you will be able to spot most of the famous "M objects,"
or Messier objects, which include open star clusters, globular
star clusters, gaseous nebulas, and even galaxies outside our
own Milky Way galaxy. You'll need a star map or a planisphere
(the Orion Star Target plansiphere is a great one) and some
patience, but the rewards are endless.
Best Targets
Best night sky targets from the city:
• The Moon
• Venus
• Jupiter
6
• Saturn
Best targets from rural locations (everything above, plus):
• The Great Nebula in Orion – a spectacular glowing cloud
of gas in Orion's sword; this is a "stellar maternity ward," a
place where new stars are forming.
• The Summer Milky Way – the GoScope is well suited
to scanning the Milky Way to "discover" dozens of star
clusters.
• The Pleiades (M45) – a bright open star cluster
• The Andromeda Galaxy (M31) – the brightest external
galaxy
• The Double Cluster in Perseus
• M11, M6 & M7 – three bright, summer star clusters
• The Beehive Cluster – A big, open star cluster in the
spring sky
• The Great Cluster in Hercules M13 – a wonderful
globular star cluster, spring & summer
• M22 – another grand globular star cluster in Sagittarius, a
summer constellation
"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 turbu-
lence causes objects viewed through the telescope to "boil." If
you look up at the sky and stars are twinkling noticeably, the
seeing is poor and you will be limited to viewing at lower magni-
fications. At higher magnifications, images will not focus clearly.
Fine details on the planets and Moon will likely not be visible.
In conditions of good seeing, star twinkling is minimal and imag-
es appear steady in the eyepiece. Seeing is best overhead,
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 "trans-
parency"—air free of moisture, smoke, and dust. All tend to scat-
ter light, which reduces an object's brightness. Transparency is
judged by the magnitude of the faintest stars you can see with
the unaided eye (5th or 6th magnitude 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. Allow at least 30 minutes for
your telescope to acclimate to the temperature outdoors before
you start observing with it.
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, galaxies,
and star clusters—or even very 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 faint-
er details in objects you view in your telescope.
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