Brightest stars Nearest Stars

1
Brightest stars Nearest
Stars
Star name Apparent Star name
distance magnitude
(ly)
Sun -26.8 Sun
- Sirius
-1.46 Proxima
Centauri 4.2 Canopus -0.72
Alpha Centauri AB 4.3 Arcturus
-0.04 Barnards stars
6.0 Alpha Centauri -0.01 Wolf
359 7.7 Vega
0.00 BD 362147
8.2 Capella 0.08
Luyten 726-8AB 8.4 Rigel
0.12 Sirius A B
8.6 Procyon 0.38
Ross 154 9.4 Betelgeuse
0.41 Ross 248
10.4
most nearby stars are too faint to see without a
telescope
2
In a volume limited sample counting all stars
Most stars are less luminous than the sun, only a
few are brighter.
3
In binary star systems we can determine the
mass of the star. For stars thar are
spectroscopically main sequence the stars
luminosity is correlated with its mass.
e.g., 10 solar masses is between 103 and 104
times more luminous than the sun. 0.1 solar
masses is down by 103
4
Stellar Lifetimes
On the main sequence i.e., for stars fusing
hydrogen
in their centers

• Luminosity is determined by mass
• If we assume that the star has a total energy
  reservoir proportional to its mass (i.e., a
  certain fraction of its mass is burns by
  nuclear reactions).

• Then the lifetime, t, is approximately given by

5
To summarize

• There are many more faint stars than bright
  ones
• Faint stars also have low mass
• Low mass stars live a long time

The converse is also true

• Bright (high luminosity) stars are rare
• Bright stars are more massive (exception red
  giants)
• Massive stars have short lives

6
Orion Nebula M-42
1600 light years away in the sword of Orion,
easily visible to the naked eye. 85 x 60 across
and part of a larger cloud spanning 20 degrees.
Diameter 30 ly, Mass 200,000 solar masses.
Star Nursary
7
Constellations
Orion Nebula
Betelgeuse and Rigel are a and b-Orionis
8
Eagle Nebula M16 7000 ly in Serpens
9
The Pleiades M45
A young cluster of stars with over 100 members, 6
to 9 of which are visible to the unaided eye
(depending on eyesight and viewing conditions.
The nebula is about 380 ly away and its members
are only about 60 80 My old. The blue color
is indicative of a Refection Nebula
10
NGC 3293
An open cluster near the Carina Nebula. These
stars are only about 5 million years old.
11
For stars lighter than about 8 solar masses...
12
After exhausting hydrogen in its center, a star
becomes a red giant.
13
A Planetary Nebula
NGC 2440
The star in the center is a white dwarf with one
of the highest known temperatures (200,000 K).
It is very young and about 250 times brighter
than the sun. Soon astronomically speaking
it will cool down and become faint.
14
The Ring Nebula M57
4100 light years distant, T 100,000 K
15
Blinking Eye Hourglass NGC 3918
Egg Cats Eye
Hubbles Double Bubble Saturn
Red Rectangle Blue Snowball
Siamese Squid
Planetary nebulae Bruce Balick www.astro.washingt
on.edu/balick/WFPC2
16
Globular Clusters
47 Tuc
M13
Second brightest globular cluster (behind Omega
Cen). There are about 200 globular clusters
altogether. This one is near the SMC in the sky
and about 20,000 ly distant. Lots of red
giants visible here.
This globular cluster in Hercules is 22,000 ly
distant and contains 105 106 stars. Age 12 to
14 billion years. It is about 150 light years
across.
17
For stars heavier than about 8 solar masses
18
For stars over 8 solar masses
19
The Crab Nebula M1
July 4, 1054 AD.
20
SN 1987A
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)