STAR: AN ASTRONOMICAL OBJECT
WHAT IS A
A Star is Born:
The Life Cycle of a Star
23
On clear nights, we can see the stars as
twinkling points of light in the sky. But
what exactly are we looking at?
A star is an astronomical object
consisting of a luminous spheroid of
gas, mostly hydrogen & helium, held
together by opposing forces of
energy. At its core, energy is created
by nuclear fusion causing the gases to
expand and exert an outward pressure.
This outward pressure is balanced by
the inward pull of gravity, leaving the
star in hydrostatic equilibrium. This
balance of forces lasts for most of a
star’s life.
The nearest star to Earth is the Sun.
Many other stars (9,096)are visible to
the naked eye at night, appearing as a
multitude of fixed luminous points in
the sky due to their immense distance
from the Earth. However, most of the
estimated 200 sextillion (2×10 ) stars
in the Universe are invisible to the
naked eye from Earth.
Historically, the most prominent stars
were grouped into constellations and
asterisms, the brightest of which
gained proper names. Astronomers
have assembled star catalogues that
identify the known stars and provide
standardized stellar designations.