Astronomy is one of the few sciences where amateurs can still
play an active role, especially in the discovery and monitoring
of transient phenomena. Astronomy is not to be confused with astrology,
which assumes that people's destiny and human affairs in general
are correlated to the apparent positions of astronomical objects
in the sky -- although the two fields share a common origin, they
are quite different; astronomers embrace the scientific method,
while astrologers do not.
Divisions of Astronomy
In ancient Greece and other early civilizations, astronomy consisted
largely of astrometry, measuring positions of stars and planets
in the sky. Later, the work of Kepler and Newton paved the way
for celestial mechanics, mathematically predicting the motions
of celestial bodies interacting under gravity, and solar system
objects in particular. Much of the effort in these two areas, once
done largely by hand, is highly automated nowadays, to the extent
that they are rarely considered as independent disciplines anymore.
Motions and positions of objects are now more easily determined,
and modern astronomy concerns itself much more with trying to observe
and understand the actual physical nature of celestial objects—what
makes them "tick".
Ever since the twentieth century the field of professional
astronomy has tended to split into observational astronomy and
astrophysics. Although most astronomers incorporate elements of
both into their research, because of the different skills involved,
most professional astronomers tend to specialize in one or the
other. Observational astronomy is concerned mostly with acquiring
data, which involves building and maintaining instruments and processing
the resulting information; this branch is at times referred to
as "astrometry" or simply as "astronomy". Theoretical
astrophysics is concerned mainly with figuring out the observational
implications of different models, and involves working with computer
or analytic models.
The fields of study can also be categorized in other ways. Categorization
by the region of space under study (for example, Galactic astronomy,
Planetary Sciences); by subject, such as star formation or cosmology;
or by the method used for obtaining information.