Distances in the Universe >> Light Years, UA and Pársec
Distances in the Universe >> Light Years, UA and Pársec
.
One Light Year (AL):
It is a unit
of astronomical distance.
It is the distance that a photon travels in a Julian year (365.25
of 86,400 s) at the speed of light in a vacuum (299,792,458 km / s) at a distance
infinite of any gravitational or magnetic field.
1 Light year equals 9''460,730'472,580.8 km (almost 10 billion
of kilometers).
The terms of:
Second Light toDistance that the light travels in a second.
Minute Light toDistance that the light travels in
one minute.
Light Hour toDistance that the light travels in
one hour
Day Light toDistance that the light travels in
one day.
A unit
Astronomical (ua):
It is the average distance between the Sun and Earth and its
approximation equals 149'597,870 km (almost 150 million kilometers).
Although it is an excellent approximation, it does not correspond with all
precision to the real orbit of the Earth. The precise definition of the System
International Units is the "radius of a Newtonian circular orbit
around the Sun of a particle with infinitesimal mass with a movement
average of .017 202 098 95 radians per day "; so
equivalent, "is the distance between the Sun and a particle without mass and free of
disturbances, which moves in a circular orbit around the Sun with a
orbital period of 365.2568983 days (Gaussian year) ".
In
Strict sense parsec is defined as the distance at which a unit
astronomic (ua) subtends an angle of one second of arc (1 ").
words, a star is a parsec if its parallax is equal to 1 second of
arc.
The
basic separation that astronomers use to determine the parallax of the
stars is the radius of Earth's orbit. Parallax is measured in
seconds of arc (60 seconds of arc = 1 minute of arc, 60 minutes of arc =
1 degree). It is based on the trigonometric parallax method, the oldest and
extended to determine the distance to the stars.
Market Stall
that the parsec is a distance related to the astronomical unit,
relates to the tangent of the angle in P (see diagram). Now, being
π (read pi) a very small angle, of the order of up to
thousandth of a second of arc, it will behave as a linear function of
inverse proportionality with respect to Δ (read delta). That is, to
Δ double, π is made half, but if Δ is half, π will be double, and so
successively, in such a way that the relationship between distance and parallax
It becomes very simple:
A
parsec is the distance from Earth to an astronomical object that has a
parallax of a second of arc.
…where
Δ is the distance in parsecs, and π the parallax in seconds of arc. Measure the
parallax of a star, you just have to calculate your inverse to have the
distance in parsecs.
Other
possibility is to define a parsec as the distance at which two objects,
separated from each other by 1 astronomical unit, they seem to be separated by a
angle of 1 second of arc. So:
360 ×
60 × 60/2 × π ua ≈ 2.06 × 105 ua ≈ 3.09 × 1016
m ≈ 3.26 light years.
The
value adopted by the International Astronomical Union: 1 pc = 3.0857 × 1016
m.
Equivalences:
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