B: TYPES OF OBJECTS TO VIEW IN A TELESCOPE
Almost every observer starts out viewing the objects in the Solar System,
or near-sky as it is termed. First are the naked-eye objects: aurorae,
noctilucent clouds, meteor showers, sun dogs and pillars, moondogs, rainbows
and the like. Telescope owners tend to see more of this stuff because
they look up!
Then there are the brightest objects in the sky—the Sun, the Moon,
the planets. These are all visible everywhere on Earth. These all display
changing features and, due to the Earth’s movement around the Sun,
appear at different times of the night throughout the year. The Moon is
especially wonderful, displaying a landscape of features to challenge
even the best observers, yet terrific in the smallest telescope. With
an appropriate solar filter, the Sun becomes the only star on which we
can see details. The brighter planets rotate under our gazes so that we
see different details from hour to hour. It’s quite a show.
The challenge objects soon follow: comets, asteroids, and planetary
moons. One could spend a lifetime within the solar system and never get
tired of the endless variety of targets.
But there’s a big Universe out there. Outside our Solar System,
the visible Universe stretches almost 14 billion light years away (or
at least it did when the light we see was emitted—when we look out
into Deep Space we are actually looking back in time—it’s
actually quite a bit larger now). First, we run into the objects in our
home galaxy, the Milky Way: We see that most of the stars we can see are
not single like our Sun, but double or multiple, and display some vivid
colors in the telescope. Many of then cluster into aggregates of stars
of from hundreds to hundreds of thousands of stars—these are the
star clusters. There are two types: the irregular groups we see mostly
confined to the plane of the Milky Way, called Open Clusters, and the
incredibly dense and populous star clusters grouped in a spherical halo
around the center of the Milky Way, called Globular Clusters. It was the
location of these Globular Clusters that convinced astronomers that the
center of our Milky Way lay 27,000 light years away toward the constellation
Also visible in our galaxy are large luminous clouds of gas and dust
called Nebulae. These can be bright if they are near to stars or dark
if they are not and instead block the light of stars behind them. There
is one type of nebula formed by an older star that has thrown off most
of its atmosphere into space—these are called Planetary Nebulae
because the astronomers of several hundred years ago thought they looked
a lot like planets in their telescopes of the time. Today, we know that
these nebulae are formed by nearly every star near the end of its life--and
that it is through these nebulae that the galaxy is enriched with heavier
atoms—the atoms that form the Earth, and you and me. Periodically,
a star throws out this envelope of gas and dust in a violent manner and
we see it brighten significantly. We then call it a Nova, or, if it is
especially violent, a Supernova.
Outside our galaxy, and away through space all the way to the edge of
the Universe, lie the nearly quadrillion other galaxies (a million billion).
Through amateur telescopes we can see only the nearest few thousand of
them. We cannot see very far into the Universe with our modest telescopes.
But there is one exception—the Quasars. Formed from extremely violent
galactic nuclei, these are visible at much greater distances. One in particular,
at a distance of nearly 2 billion light years (yes, looking back in time
2 billion years), is visible in a telescope as small as 5”. We should
be glad that these violent events apparently occurred when the Universe
was much younger. Life on Earth is very fragile on a galactic scale.