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Slide 1

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Parsec and Parallax
The word "parsec" comes
from "parallax of one arc
A parallax is the apparent
movement of an object,
caused by the movement
of the observer.…read more

Slide 2

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Calculating the parallax angle
The parallax angle is half the
angle moved against distant
background stars over 6
months (at the opposite ends
of the earth's orbit). The
nearer an object is to you,
the greater the angle.
The angle is often
measured in arcseconds
rather than degrees...
1 arcsecond (1") =
(1/3600)…read more

Slide 3

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Calculating the parallax angle
The parallax angle
-Stars further away appear to The apparent
move less, so they have a movement of the
smaller angle. star
-Stars nearby appear to move
more, so they have a greater
angle.…read more

Slide 4

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Discovery of `parsec'
Ancient astronomers tried
to measure the parallax of
stars via careful naked-eye
observations but failed.
Friedrich Wilhelm Bessel
was the first to measure
the parallax of a star
(Cygni 61) in 1838,
therefore making it
possible to calculate its
distance.…read more

Slide 5

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Discovery of `parsec'
Though parsec may have been
used before, the term parsec was
first mentioned in an astronomical
publication in 1913. Astronomer
Royal Frank Dyson expressed his
concern for the need of a name for
that unit of distance. He proposed
the name astron, but mentioned
that Carl Charlier had suggested
siriometer and Herbert Hall Turner
had proposed parsec. Turner's
proposal stuck…read more

Slide 6

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A parsec (pc) is the distance to a
star with a parallax angle of 1
arcsecond (or 3.26 light years).
Astronomers used parsec when
calculating the distance of far
away stars.
You can calculate the distance of stars
(in parsecs) by using this equation...
Distance (pc) = 1/angle (arcseconds)…read more

Slide 7

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Slide 8

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