Transcript The Night Sky

The Night Sky
Big Questions:
• What do we see when we look at the night
sky with the naked eye?
• How are stars named?
• Why is the apparent magnitude of stars only
a relative measurement? What is it relative
to?
• What are constellations?
• How has human culture influenced how we
name and label objects in the sky?
The night sky…
• Most of what we see when we look at the
night sky are stars - spheres of gas that
give off light energy
• Also visible (at least some of the time)
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o
o
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o
o
Planets
The Moon
Comets
Meteors (briefly visible)
Nebulae
Star clusters
Part of our galaxy (the Milky Way)
Other galaxies
Star Names
• There are multiple systems that have been
used to name stars from ancient times to
today
• Brighter stars tend to have many names…
Vega, the fourth brightest star in the sky, has
over 40 different names!
• Today, star names are assigned by the
International Astronomical Union. You can’t
pay to “name a star” (at least, not officially)
Common names:
• The brightest stars in the sky were named thousands of
years ago
• Most common star names that we use today come
from ancient Arabic, because those records survived
the Dark Ages and were translated into Latin
Modern Name
Arabic Name
Meaning
Aldebaran
Ad-Dabaran
"Follower" of the Pleiades
Betelgeuse
Yad al-Jauza'
Hand of Orion, or armpit of the giant
Rigel
Ar-Rijl
The foot
Dubhe
Ad-Dubb
The bear
Scientific names:
• In the 1600s, an attempt was made to bring order to star
names. Stars were named using a Greek letter (a, b, g) in
order of their relative brightness within a given
constellation. Alpha is the brightest, Beta is second
brightest, etc. The Greek letter is followed by the Latin
possessive form of the constellation
Betelgeuse
In the Constellation Orion:
Betelgeuse = a Orionis
Rigel = b Orionis
Rigel
Star Catalogs:
• Star catalogs have also been created,
listing stars according to various criteria
(position in its constellation, distance from Earth,
coordinates in the sky, etc.)
• So the star Vega is also known as
o
o
o
o
o
o
alpha Lyrae
3 Lyrae
BD +38°32’38”
HD 172167
SAO 067174
And MORE!
Projection Effect
• The stars in a constellation
appear to be projected
onto the flat surface of
the sky
• In truth, the stars in the
same constellation are
often located at very
different distances from
Earth
• https://www.youtube.co
m/watch?v=pXDyzSkxFvs
The Magnitude Scale
• First introduced by Hipparchus (160 - 127 B.C.E.)
o Brightest stars --1st magnitude stars
o Faintest stars seen with unaided eye-- 6th magnitude
o So … smaller numbers = brighter
• This measures Apparent Visual
Magnitudes based on what we can see
from Earth with the naked eye
Today’s Apparent Magnitude Scale
• As our understanding of the universe has evolved,
the magnitude scale has been expanded
o negative numbers for extremely bright objects
o larger numbers for dim objects not visible to the
naked eye
Apparent Magnitude
vs. Luminosity
• Apparent Magnitude – how bright it
looks from Earth
o Betelgeuse has an apparent magnitude of 0.45
o The sun has an apparent magnitude of -26
• Luminosity – how much light it actually
gives off
o Betelgeuse is actually about 10,000 times more
luminous than the sun
o Distance makes the difference!
Constellations
• In ancient times, constellations only referred to the
brightest stars that appeared to form images, and
were often associated with mythological figures.
• Babylonian, Egyptian, and Greek astronomers
named many of the constellations we know today
• 48 ancient constellations are still in use
Naming constellations:
• Culture influenced the patterns and
mythology of the constellations
o The Greeks saw Orion the Hunter, while the
Lakota tribe saw the Great Hand, a symbol of
peace between the gods and man
o Romans and Iroquois both saw a bear in Ursa
Major, but told different stories about it
o Most of the names and myths we know today
have Greco-Roman origins because those
cultures kept many written records
Modern Constellations
• In 1922 the International
Astronomical Association
(IAU) established a total
of 88 official
constellations with clear
boundaries
• Today’s constellations
represent an area of the
sky – not just a group of
stars
• Each celestial object is
part of only one
constellation
Asterisms:
• Recognizable patterns in the stars
o The Big Dipper is an asterism within the Big Bear, which itself
is an asterism within the constellation Ursa Major (that entire
section of sky)
o What most people call “constellations” are technically
asterisms
Note the
yellow
border of the
constellation,
with the bear
and big
dipper
asterisms
inside
Crash Course Video
• https://www.youtube.com/watch?v=LWtlev6suc&list=PL8dPuuaLjXtPAJr1ysd5yGIyiSFuh0mI
L&index=2
Big Questions:
• What do we see when we look at the night
sky with the naked eye?
• How are stars named?
• Why is the apparent magnitude of stars only
a relative measurement? What is it relative
to?
• What are constellations?
• How has human culture influenced how we
name and label objects in the sky?