Download I. Parallax

Parallax, Magnitudes, Spectral Types and HR Diagram
I. Parallax
A. Parallax is the _________________ to determine the
________ to stars. Parallax only works for _________ stars.
B. Parallax is the apparent ______ of a “nearby” star with
respective to the background stars when viewed ______
_______________. Because of Earth’s orbit around the Sun,
this happens when astronomers view a “nearby” star at ___
_________________________.
C. An example of this is when you hold your finger ___________
________________and view it first with ________ and then
the _________.
D. The term parallax is derived from the Greek word “parallaxis”,
which means _________.
E. Nearby objects have a ______ parallax than more distant
objects. Therefore, the further away a star is, the _____
___________ to measure its parallax.
F. ESA’s Hipparcos satellite has used parallax to determine the
distance of the closest _________ stars to the Sun. It had
the ability to measure stellar shifts equivalent to the width of
_________________________!
G. ESA’s next parallax mission, Gaia, was launched Dec 19, 2013.
It will determine the distance to the closest ________ stars.
It will be able to measure a star’s position to the equivalent of
the width of _________________________!!
H. The parallax method is extremely important not only because it
is the only direct method for determining stellar distances, but
also because it ______________ for checking the validity of
the other ________ distance measuring techniques.
II. Stellar Magnitudes
A. The magnitude of a star is a description of how _______ a star
is.
B. The scale was initially set up by Norman Pogson in 1856 with a
magnitude ___ given to the brightest star in the sky and a
magnitude ___ being the dimmest star that could be seen ____
____________.
C. The apparent magnitude of a star is a measure of its brightness
_________________. The brighter an object appears, the
______ the value of its magnitude. For example, ___________
______ and __________________.
D. The absolute magnitude of a star is a measure of its _______
_________. It is a measure of a star’s brightness from a fixed
distance of __________________. Note that the absolute
magnitude of a star is equal to the apparent magnitude if the
observer is at a distance of 10 parsecs from the star.
Table Comparing Apparent versus Absolute Magnitudes
Star
Apparent Magnitude
Absolute Magnitude
Sun
-26.7
+4.83
Full Moon
-12.6
Venus
-4.6
Mars
-2.9
Jupiter
-2.9
Sirius A
-1.44
+1.45
Arcturus
-0.05
-0.31
Vega
+0.03
+0.58
Betelguese
+0.45
-5.14
Antares
+1.06
-5.28
Deneb
+1.25
-8.73
E. The Hubble Space Telescope
has observed stars with
magnitudes down to ____ at
visible wavelengths and the Keck
telescopes have located similarly
faint stars in the infrared with
_________________.
F. There is a _________
difference in brightness for
stars that differ by a
_____________. For example,
a star of magnitude 1 is 100
times as bright as a star with
magnitude 6.
Hubble Space Telescope
Keck Telescopes
III. Spectral Classes
A. Stars are classified largely by their ___________________.
This is precisely measured by observing their ____________
___________.
B. A star’s color and temperature is determined ______________
_______. The more massive a star is, the _________________
it is.
C. Most stars are currently classified using the letters O, B, A, F, G, K
and M, where O stars are the ________ and M stars are the
_______.
D. The order of these letters can be remembered by this mnemonic:
_____________
_____________
_____________
_____________
_____________
_____________
_____________
E. General Trends:
O
B
A
F
G
B
K
A
M
F G K M
IV. HR Diagrams
A. HR Diagrams are to __________ as the _____________
___________.
B. The HR diagrams where developed by ________________
and __________________.
C. The Hertzsprung–Russell diagram is a scatter graph of stars
showing the relationship between the stars' ______
____________________ versus their ______________
_________________.
D. The HR diagrams represented a major step towards an
understanding the _______________.