consult a monthly astronomy magazine, such as Sky and Telescope or Astronomy. Listed below are the best
planets for viewing through the ETX-90EC.
Venus
is about nine-tenths the diameter of Earth. As Venus orbits the Sun, observers can see it go through phases
(crescent, half, and full) much like those of the Moon. The disk of Venus appears white as sunlight is reflected off
the thick cloud cover that completely obscures any surface detail.
Mars
is about half the diameter of Earth, and appears through the telescope as a tiny reddish-orange disk. It may be
possible to see a hint of white at one of the planet's polar ice caps. Approximately every two years, when Mars is
closest to Earth in its orbit, additional detail and coloring on the planet's surface may be visible.
Jupiter
is the largest planet in our solar system and is 11 times the diameter of Earth. The planet appears as a disk
with dark lines stretching across the surface. These lines are cloud bands in the atmosphere. Four of Jupiter's 16
moons (Io, Europa, Ganymede, and Callisto) can be seen as "star-like" points of light when using even the lowest
magnification. These moons orbit Jupiter so that the number of moons visible on any given night changes as they
circle around the giant planet.
Saturn
is nine times the diameter of Earth and appears as a small, round disk with rings extending out from either
side. In 1610, Galileo, the first person to observe Saturn through a telescope, did not understand that what he was
seeing were rings. Instead, he believed that Saturn had "ears." Saturn's rings are composed of billions of ice
particles ranging in size from a speck of dust to the size of a house. The major division in Saturn's rings, called the
Cassini Division, is generally visible through the ETX-90EC. Titan, the largest of Saturn's 18 moons can also be
seen as a bright, star-like object near the planet.
Deep-Sky Objects
Star charts can be used to locate constellations, individual stars and deep-sky objects. Examples of various deep-
sky objects are given below:
Stars
are large gaseous objects that are self-illuminated by nuclear fusion in their core. Because of their vast
distances from our solar system, all stars appear as pinpoints of light, irrespective of the size of the telescope used.
Nebulae
are vast interstellar clouds of gas and dust where stars are formed. Most impressive of these is the Great
Nebula in Orion (M42), a diffuse nebula that appears as a faint wispy gray cloud. M42 is 1600 light years from Earth.
Open Clusters
are loose groupings of young stars, all recently formed from the
same diffuse nebula. The Pleiades (Fig. 18) is an open cluster 410 light years
away. Through the ETX-90EC several hundred stars are visible.
Constellations
are large, imaginary patterns of stars believed by ancient
civilizations to be the celestial equivalent of objects, animals, people, or gods.
These patterns are too large to be seen through a telescope. To learn the
constellations, start with an easy grouping of stars, such as the Big Dipper in
Ursa Major. Then, use a star chart to explore across the sky.
Galaxies
are large assemblies of stars, nebulae, and star clusters that are bound by gravity. The most common
shape is spiral (such as our own Milky Way), but galaxies can also be elliptical, or even irregular blobs. The
Andromeda Galaxy (M31) is the closest spiral-type galaxy to our own. This galaxy appears fuzzy and cigar-shaped.
It is 2.2 million light years away in the constellation Andromeda, located between the large "W" of Cassiopeia and
the great square of Pegasus. Under clear, dark conditions, M31 can be seen with the naked eye and is a fascinating
object through the ETX-90EC.
Fig. 18: The Pleiades Star Cluster (M45) in
the constellation Taurus.
