**13.2 - Measuring Distances in Space**

**Presented by Galia & Daphne**

**Topic to Cover:**

**-measuring distances in space**

**-baselines and parallax**

**-Cepheid variables**

**-red shifts of galaxies**

So how big is the entire universe?

light year

-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!

http://scaleofuniverse.com/

Earth

Sun

How did scientists measure such vast distances?

Measuring Distances in Space

Baselines and Parallax

Red Shift

Cepheid Variables

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

object

Trigonometry can be used to determine the lengths of distant objects using the baseline.

Using baselines

diameter of Earth's orbit (baseline)

object in space

Baseline

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,

dimmer Cepheids

Standard Candles

-objects of either known brightness or predictable behaviours that astronomers use to determine distance

Absolute Magnitude

Apparent Magnitude

-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.

5m

200m

50m

5m

baseline

that must be known

line

forming

a

right

triangle

measure the angle

using the calculations of a triangle's degrees, this angle is determined

7m

Moon

36m

300m

Pluto

2000km

Proxima Centauri

Alpha Centauri B

Alpha Centauri A

<2cm

Jupiter

3.6 km/h by model

Joe

-reach pluto in 5 min

-Proxima Centauri in about 23 days

-but after walking 24 days, Joe only reaches

our closest star neighbours

"Universe"

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.

closer

farther

-complicated math

-estimates

-takes time (6 months apart for the use of Earth's baseline)

-mistakes

The beginning

?

**The end!**