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13.2 - Measuring Distances in Space
Transcript of 13.2 - Measuring Distances in Space
Presented by Galia & Daphne
Topic to Cover:
-measuring distances in space
-baselines and parallax
-red shifts of galaxies
So how big is the entire universe?
-the distance light travels in one year
-speed of 3.0 x 10^5 km/s
One light year would be 9.5 x 10^12 km.
So, the volume of the universe is around 1 x 10^30 cubic light years!
How did scientists measure such vast distances?
Measuring Distances in Space
Baselines and Parallax
-the apparent motion of a nearby star against
the background of more distant, non-moving stars.
-unit of parsec = 3.26 light years.
-an imaginary line from which the distance to an object is measured
-length of baseline is known
Trigonometry can be used to determine the lengths of distant objects using the baseline.
diameter of Earth's orbit (baseline)
object in space
Although the parallax method is effective, it only works well out to 200 light years. This is because the greater the distance, the smaller the angles formed.
Cepheid Variable Stars
-one of the standard candles of the universe
-unstable, yellow supergiant stars
-pulses, changing in size and brightness
-large Cepheids pulse more slowly than small,
-objects of either known brightness or predictable behaviours that astronomers use to determine distance
-actual amount of light the star gives off
-amount of light appearing in sky
How do astronomers determine the distance from Earth?
By using Cepheid variable stars and comparing its absolute magnitude and apparent magnitude!
So if astronomers compared those two, they would be able to find out vast distances, because light fades with increasing distance.
that must be known
measure the angle
using the calculations of a triangle's degrees, this angle is determined
Alpha Centauri B
Alpha Centauri A
3.6 km/h by model
-reach pluto in 5 min
-Proxima Centauri in about 23 days
-but after walking 24 days, Joe only reaches
our closest star neighbours
best estimate of stars: 1.0 x 10^22 stars
-similar to the use of Cepheid variables because of similar light and wavelength characteristics
-for example, the farther the object's spectral lines are shifted to the red end means the faster the object is moving away
-that means the more red it is, the more distant
The closer the spectral line is to red, the faster the galaxy is moving.
Since the galaxy is moving faster, it would also be farther away.
-takes time (6 months apart for the use of Earth's baseline)