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1.3.
Distances in the Universe
The Universe is so immense that in order to measure distances between galaxies,
we need to use different units of measurement to those we use to measure
distances on Earth. These units are the light year and the parsec. To measure
shorter distances, such as those between the stars and planets of our Solar system,
we use astronomical units.
1.3.1.
Light year
A
light year
is equivalent to the distance travelled by light in one year. Light
travels at a speed of 300000 km per second.
A
parsec (pc)
is equivalent to 3.26 light years. It is usually used to measure very
large interstellar distances.
An
astronomical unit (AU)
is the distance between the Earth and the Sun. Its
value is equivalent to approximately 150000000 km.
Analyse
3.
Jupiter is around 5.19AU
from the Sun. Howmany
thousands of kilometres
is this equivalent to?
Apply
4.
Put
the
following
distances in order from
largest to smallest: 1500
million km, 2 light years
and 0.5 pc.
5.
If the distance between
Mars and the Sun is 228
million kilometres, how
far is the Earth fromMars
in millions of kilometres?
How many AU units is
the distance calculated
equal to?
6.
How many AU are there
in a light year? Howmany
kilometers are equal to a
parsec?
7
To have an idea of how far light travels in one year, first we need to find out how
many seconds there are in this period of time.
Given that a year has 365 days, we make the following calculations:
1 year = 365 days
365 days x 24 hours = 8760 h/year
8760 hours x 3 600 s/hour = 31536000 s/year
Once we have already calculated howmany seconds there are in a year, and knowing
that light travels 30 0000 km per second:
31536000 s/year x 300000 km/s = 9460800000000 km
This means that in one second light travels approximately 9.5 billion kilometres.
1.3.2.
Parsec
For example, the closest star to the Solar System is Proxima Centauri, which is 1.31
parsecs or 4.28 light years away.
1.3.3.
An astronomical unit
The enormous distance between the stars and the planets in our Solar System
means that the light we see from the stars is light they produced in the past,
and even the light of stars that are now extinct. It is the same with light from
the Sun.
We know that Earth is 1 AU (150 000 000 km) from the Sun. We also know that light
travels at 300 000 km/s. So:
150000000 km = 500 s = 8.33 min
300000 km/s
That means that the light from the Sun takes a little more than 8 minutes to reach
our planet.
