Transcript ASTR 1101-001 Spring 2008 - Louisiana State University

ASTR 1102-002
2008 Fall Semester
Joel E. Tohline, Alumni Professor
Office: 247 Nicholson Hall
[Slides from Lecture03]
University-wide, Gustav-motivated
Calendar Modifications
University-wide, Gustav-motivated
Calendar Modifications
Gustav’s Effect on this Course
• Fall Holiday has been cancelled, which means
our class will meet on Thursday, 9 October.
(This makes up for one class day lost to Gustav
last week.)
• We will hold an additional makeup class on
Saturday, 20 September! (This will account for
the second class day lost to Gustav last week.)
• Date of Exam #1 has been changed to Tuesday,
23 September!
Course Syllabus
Course Syllabus
Chapter 17: The Nature of Stars
Describe a Population of Stars
Individual Stars…
• Location in Space
– Coordinate (angular) position on the sky
[Right ascension & Declination]
– Distance from Earth
[use Stellar Parallax]
• Motion through Space
– Motion across the sky
[“proper” motion]
– Motion toward/away from us (radial velocity)
[use Doppler Effect]
Google Earth/Sky
Stellar Parallax (§17-1)
• Understand Figs. 17-1, 17-2, and eyes+thumb
illustrations.
• Star ‘A’ exhibits a stellar parallax that is twice as
large as the stellar parallax exhibited by star ‘B’.
– Which star is farther from us?
– How much farther away?
• If parallax angle (p) is measured in arcseconds
and distance is measured in ‘parsecs’ (see §1-7
and Fig. 1-14), then ...
–
d = 1/p
Stellar Parallax (§17-1)
• Understand Figs. 17-1, 17-2, and eyes+thumb
illustrations.
• Star ‘A’ exhibits a stellar parallax that is twice as
large as the stellar parallax exhibited by star ‘B’.
– Which star is farther from us?
– How much farther away?
• If parallax angle (p) is measured in arcseconds
and distance is measured in ‘parsecs’ (see §1-7
and Fig. 1-14), then ...
–
d = 1/p
March sky image
September sky image
Stellar Parallax (§17-1)
• Understand Figs. 17-1, 17-2, and eyes+thumb
illustrations.
• Star ‘A’ exhibits a stellar parallax that is twice as
large as the stellar parallax exhibited by star ‘B’.
– Which star is farther from us?
– How much farther away?
• If parallax angle (p) is measured in ‘arcseconds’
and distance is measured in ‘parsecs’ (see §1-7
and Fig. 1-14), then ...
–
d = 1/p
Individual Stars…
• Location in Space
– Coordinate (angular) position on the sky
[Right ascension & Declination]
– Distance from Earth
[use Stellar Parallax]
• Motion through Space
– Motion across the sky
[“proper” motion]
– Motion toward/away from us (radial velocity)
[use Doppler Effect; §5-9]
Motion Across the Sky
(“proper” motion)
http://www.psi.edu/~esquerdo/jim/astfov.gif
Prominent and Obscured Objects
Prominent and Obscured Objects
NOTE:
Transient Events (in time) also occur
NOTE:
Transient Events (in time) also occur
NOTE:
Transient Events (in time) also occur
NOTE:
Transient Events (in time) also occur
NOTE:
Transient Events (in time) also occur
Individual Stars…
• Location in Space
– Coordinate (angular) position on the sky
– Distance from Earth
• Motion through Space
– Motion across the sky (“proper” motion)
– Motion toward/away from us (radial velocity)
• Intrinsic properties
–
–
–
–
Brightness (luminosity/magnitude)
Color (surface temperature)
Mass
Age
Stars of different brightness
Stars of different colors
Apparent brightness due to…
• Each star’s intrinsic brightness
• Each star’s distance from us
Apparent Brightness varies with
Distance
Color-Temperature Relationship
More About: Continuous Spectra from
Hot Dense Gases (or Solids)
• Kirchhoff’s 1st Law: Hot dense gas produces a
continuous spectrum (a complete rainbow of colors)
• A plot of light intensity versus wavelength always has the
same general appearance (blackbody function):
– Very little light at very short wavelengths
– Very little light at very long wavelengths
– Intensity of light peaks at some intermediate wavelength
• But the color that marks the brightest intensity varies
with gas temperature:
– Hot objects are “bluer”
– Cold objects are “redder”
The Sun’s Continuous Spectrum
(Textbook Figure 5-12)
Wien’s Law for Blackbody Spectra
• As the textbook points out (§5-4), there is
a mathematical equation that shows
precisely how the wavelength (color) of
maximum intensity varies with gas
temperature.