Download Sequence of Stars Notes

Apparent Magnitude: how bright a star is
as seen from Earth, depends on star’s
actual brightness and distance from
Earth
 Absolute Magnitude: how bright a star
actually is, with no regard to distance

Magnitude of Common Celestial
Objects
Object
Apparent Magnitude
Absolute Magnitude
Sun
-27
5
Full Moon
-13
n/a
Sirius
-1.5
1.4
Rigel
.1
-7.0
Betelguese
.9
-6.0
The faintest stars visible to the naked eye have an apparent
magnitude in the range of 3-4.
Stellar Evolution

Ancient White Dwarf Stars
in the Milky Way Galaxy
Stars differ in:
 Temperature
 Size/mass
 Magnitude
 Elements
 Color
 Age

Age of a star affects the temperature,
size/mass, and magnitude!
H-R Diagram:
shows the
relationship
between a
star’s
absolute
magnitude
and
temperature
Hot Stars are brighter…
Giants are cool, but bright
because of their size.
White dwarfs are very
hot but dim. They are
the oldest stars.
Most Stars are on the Main
Sequence.
While cool stars are
dimmer.
http://sunshine.chpc.utah.edu/labs/star_life/support/HR_animated.swf
Star Evolution

Nebula/Nebulae
 A large cloud of gas and dust in space that
may become the beginning of a star
 The clouds of gas and dust exert a
gravitational force on each other and the
nebula begins to contract
Star Forming Area in Eagle Nebula
Star Evolution

Red Giant
 A star that has become redder and brigher
as it nears the end of its life
 Temperature between 3,100 and 5,800
degrees Fahrenheit
Red Giant Monocerotis
Star Evolution

White Dwarf
 When a star uses up its supply of helium, it
contracts and the outer layers escape into
space, leaving a hot, dense core
 Approximately the size
of Earth
 Does not lie on the
main sequence, is hot,
but dim
Faint White Dwarf Stars in Globular Cluster NGC 6397
Star Evolution

Supernova
 Can only occur if the star has become a
supergiant
 When a star’s core collapses, the outer
portion explodes
 Becomes either a black hole or a neutron
star (depending on mass of original star)
The Cygnus Loop Supernova Remnant
Star Evolution

Neutron Star
 A supernova that shrinks to about 10-15 km
in diameter
 The core becomes so dense that only
neutrons can exist there
 The final stage in the life cycle of some stars
Star Evolution

Black Holes
 An object so dense that nothing, including
light, can escape its gravity field
Dust Disk around Black Hole in Galaxy NGC 4261
Star Evolution

Black/Brown Dwarfs
 A white dwarf that has cooled down enough
that it no longer produces light from the heat
 Have a low mass
 Often referred to as failed stars
Star Catalogues

M = Messier objects
 Objects first listed by a French astronomer,
Charles Messier, in 1774.
 110 Objects Total
Star Catalogues

Andromeda Galaxy,
NGC 224/M 31
NGC = New General Catalogue
 Compiled in the 1880’s by J.L.E. Dreyer
 Total of 7,840 objects
 Largest comprehensive
catalog of deep sky objects
Sculptor Galaxy, NGC 253
Star Catalogues
 Supplement to the NGC published in 1895
 Catalogs 5,387 galaxies, nebulae, and star
clusters
Irregular Galaxy IC10
IC 4406 (Planetary Nebula)