A modern value is
1 AU = 149; 597; 870 1 km :
1.2.3 Newton's Law of Gravitation gives mass of Sun
Given the AU, we can use Newton's Law of Gravitation to get the mass of
the Sun. This is probably the rst example of true astrophysics:
f ) Astronomy and astrophysics generally assumes the Copernican principle:
WE ARE IN NO FAVORED POSITION IN THE UNIVERSE.
so the Universe near us and physics near us are typical of contemporaneous parts of the Universe | unless, of course, we nd factual e
1.2.2 Parallax of Mars, transits of Venus determine scale
Putting a scale on things requires that any one distance be known both in
AU and in km.
1671: French expedition to Cayenne (French Guiana, home of hot peppers) measured parallax of Mars at oppositi
First parallaxes date from 1839cfw_1840: Bessel, von Struve. Technology
note: both used lenses made by Fraunhofer (Bavaria).
1.2.6 Luminosities in modern units (watts)
We never did get L in watts (or erg/s) because we got sidetracked into
Note there is a geometrical magnication factor that helps:
D = 0:72 :
So from dierent latitudes on one sees dierent tracks.
Separation is here
It is only
~ 1 Venus diameter.
How to measure small separation from opposite sides of gl
Huygens also thought that Sirius (modern mV = 1:45) was as bright as a
candle at 80 m. So, if it was same intrinsic brightness as Sun:
DSirius = 127000 29000 AU
1 light year.
We now know that the actual distance to Sirius is 550000 AU (8
1 lumen = light emitted by 60 cm2 blackbody
at the melting point of platinum, 2044 K
1 lux = 1 lumen/m2 1 candle at 1 m
A bright (mV = 0) star is 2:5 10 6 lux.
A good VCR camera (with a charge-coupled device (CCD) works down
to 5 lux. Use a pinhole to g
1.1 Astronomy and Astrophysics
1.1.1 What distinguishes them? What are they?
the art of observation and the measurement side of the subject
radio, optical, IR, UV, x-ray, -ray, neutrino, gravity-wave studies
b) Systems are often complicated, and we cannot always conduct experiments to isolate the relevant variables/parameters. The observations
that astronomy provides are often very inaccurate and incomplete, so
we often need only work to low accuracy (order o
2 The Astronomical Context
Here we learn more about available types of astronomical data, in order from
easy to dicult.
2.1 Angular and positional measurements
2.1.1 Angles between objects measured \on the sky" cfw_ i.e., in
View in Sky