STARS AND GALAXIES
Stars are formed from
the matter which is supposed to have originated from the
interstellar dust which was the by product of Big Bang. All of
the stars that have names (about 2-300 of them)
and were named between 500 and 2000+ years ago.
Most of the star names in use today came from
Arabic names. These days, all stars are named
for their coordinates by the IAU (International
Astronomical Union).
We are in the
milky way Galaxy at about half way from the
middle to the edge on one side. The illuminated
strip we see in the sky as the Milky Way, is the
light from many of the stars in our almost
disk-shaped galaxy. The Milky Way virtually
wraps around the whole sky because of the three
dimensional shape. Cosmic dust and the dark
matter in the Galaxies makes them opaque, so we
can only see about 5-10% of the way across with
visible-light telescopes. The radio and infrared
telescopes penetrate farther.
Right
Ascension and Declination are coordinates which
identify a star’s location in the sky. RA is
similar to longitude on the Earth while Dec is
like latitude. However, while Dec is measured in
degrees, arcminutes and arcseconds, RA is
measured in hours minutes and seconds. To
convert to degrees, multiply the RA by 15 (since
360 degrees divided by 24 hours is 15).
B and V
are measures of a star’s brightness through a
mostly blue and mostly green filter
(respectively). The brightness is measured in
magnitudes, which are a somewhat complex
concept. Briefly, a lower (or more negative)
magnitude is brighter and a larger magnitude is
fainter. It’s on a logarithmic scale though. B-V
is an approximate measure of the color of a star
(low means blue, high means red).
Spectral
type is a measure of the kind of star. They go
in the following order: O, B, A, F, G, K, M. O
stars are typically
the brightest, bluest, most
massive and shortest lived stars. M stars on the
other hand are often the faintest, reddest,
least massive and longest lived. The Sun is a G
star, so it is somewhere in the middle.
The letters
don’t actually mean anything. They were chosen
before astronomers really understood stars. The
stars were classified as A, B, C, etc. Later,
when star temperatures were figured out, they
reordered them. The number following the letter
is the subclass. For example, within G, stars
are further classified from G0 to G1 through G9
from hottest to coolest. The Sun is a G2. The
last letter is a Roman numeral indicating the
type of star from I (supergiant) to III (giant)
to V (normal, but called “dwarf”) to VI
(subdwarf).
The
flickering of the stars we see is due to
turbulence in the atmosphere. It’s just like how
things look wavy when you look over a hot grill
in the
summer, only on a smaller scale. An even
better analogy is that looking at stars from
inside our atmosphere is like birdwatching from
the bottom of a swimming pool: the ripples
distort the picture. That’s one of the main
reasons why space telescopes, like Hubble,
provide such sharp pictures.
In addition
to contributing turbulence, the atmosphere also
acts like a prism when you look at stars near
the horizon. Since the star colors get split
into a rainbow plus the turbulence makes the
star move around, it can appear like the star is
changing color.
The Zodiac is the
ring of constellations that the Sun seems to
pass through each year as the Earth orbits
around it. Contrary to popular belief, there are
actually 13 zodiacal constellations, if you pay
attention to the way astronomers define them. In
addition to Capricornus, Aquarius, Pisces,
Aries, Taurus, Gemini, Cancer, Leo, Virgo,
Libra, Scorpius, and Sagittarius; the Sun also
passes through
Ophiuchus.
All the
“Signs of the Zodiac” are off by about one
month. (hint: astrology was invented more than
2000 years ago and the precession of the Earth’s
pole has caused changes in the positions of the
stars since then).
The path the
Sun follows is called the
ecliptic.
The ecliptic plane is the plane defined by the
Earth’s orbit around the Sun. All of the planets
except Pluto orbit very near the ecliptic plane,
so you will usually find all of them in zodiacal
constellations.
Common
FAQ’s about Stars Answered
By Chris Dolan
