Download Stellar Properties

Stellar
Measurements
and Properties
How many stars can you see on a given night?
• 8,741 visible stars.
• But we don’t see half, due to our Hemispheric
sight. 8,741/2 = 4,370
• But that is the entire count and we only see half at
any given time on earth.
• 4,370/ 2 = 2,185
• Not yet…also limited by our technological
advancements.
• Answer about 1,500 – 2,000 depending on your
limiting factors
Limiting factors
Absolute vs. Apparent magnitude
• apparent magnitude of a celestial body is
a measure of its brightness as seen by an
observer on Earth. The brighter the object
appears, the lower the value of its
magnitude.
• absolute magnitude measures a celestial
object's true brightness from a set distance.
Luminosity
Luminosity - a measure of the total amount of
energy radiated by a star or other celestial
object per second. This is the power output
of a star.
Star
Magnitude
Logarithmic scale of
How Much Brighter
2.512 X between magnitude
than a Sixth Magnitude
Six Star Magnitude Table
levels
Star
Starting at Sixth Magnitude
1
100 Times
2.51 x 2.51 x 2.51 x 2.51 x 2.51
2
39.8 Times
2.51 x 2.51 x 2.51 x 2.51
3
15.8 Times
2.51 x 2.51 x 2.51
4
6.3 Times
2.51 x 2.51
5
2.51 Times
2.51 x
6
Photon: The smallest (quantum) unit of
light/electromagnetic energy. Photons
are regarded as particles with zero mass
and no electric charge.
d=1
B=1
d=2
B=1/4
d=3
B=1/9
Eclipsing Binary
4
Brightness
3
1
2
1
3
2
Time
4
Eclipsing Binary: Rare binarystar system that is aligned in
such a way that from Earth we
periodically observe one star
pass in front of the other,
eclipsing the other star
Cepheid Variable
• A Cepheid is usually a giant yellow star,
pulsing regularly by expanding and
contracting, resulting in a regular oscillation
of its luminosity.
• This type of star is helpful in determining
distances. A.k.a: stellar “Ruler”
Parallax
• Astronomers can measure
parallax by measuring the
position of a nearby star
with respect to more distant
stars behind it.
• Then measuring those
distances again six months
later when the Earth is on
the opposite side of its orbit.
Method of Trigonometric
Parallaxes
June
p
December
Foreground
Star
Distant Stars
D= 1 / P (where p= arc sec)
Closer stars have larger parallaxes:
Distant stars have smaller parallaxes:
Sample Stellar calculations
• Star A has a parallax angle of 0.742 arcsec.
• Star B has a parallax angle of 0.5 arcsec.
• Which star is further?
• How much further?
Bright, Brighter, Brightest
• Castor = 1.16
• Pollux = 1.58
• Which star is brighter?
• How much brighter?
H–R Diagram
Supergiants
Luminosity (Lsun)
106
104
102
Ma
in
1
Giants
Se
qu
en
ce
102
104
40,000
White Dwarfs
20,000
10,000
5,000
Temperature (K)
2,500
The Spectral Sequence
O
B
Hottest
50,000K
Bluest
A
F
G
K
M
L
Coolest
1300K
Reddest
Spectral Sequence is a Temperature Sequence
White Dwarf
Sirius B
M  1.0 Msun
R  5800 km
Crab Nebula
Remnant of Supernova in 1054 AD
Neutron Star
M=1.5 Msun
R10 km
(spaceimaging.com)
Neutron Star vs. Black Hole
Manhattan
(spaceimaging.com)
Neutron Star
M=1.5 Msun
R=10 km
Black Hole
M=1.5 Msun
RS=4.5 km