Topicmdf5cb51c837bab62_1528449000663_0Topic

Escape of galaxies and Hubble's law

Levelmdf5cb51c837bab62_1528449084556_0Level

Third

Core curriculummdf5cb51c837bab62_1528449076687_0Core curriculum

IV. Gravity and elements of astronomy. The student:

5) describes the Big Bang as the beginning of the Universe; knows the approximate age of the Universe, describes the expansion of the Universe (the escape of galaxiesescape of galaxiesescape of galaxies); applies Hubble's law to calculations.

Timingmdf5cb51c837bab62_1528449068082_0Timing

45 minutes

General learning objectivesmdf5cb51c837bab62_1528449523725_0General learning objectives

Describes the expansionexpansionexpansion of the Universe.

Key competencesmdf5cb51c837bab62_1528449552113_0Key competences

1. Describes how the escape of galaxiesescape of galaxiesescape of galaxies can be determined.

2. Applies Hubble’s law to calculations.

Operational (detailed) goalsmdf5cb51c837bab62_1528450430307_0Operational (detailed) goals

The student:

- explains how the escape of galaxiesescape of galaxiesescape of galaxies can be determined,

- explains the Hubble’s law.

Methodsmdf5cb51c837bab62_1528449534267_0Methods

1. Discussion.

2. Text analysis.

Forms of workmdf5cb51c837bab62_1528449514617_0Forms of work

1. Individual work.

2. Group work.

Lesson stages

Introductionmdf5cb51c837bab62_1528450127855_0Introduction

The students remind the structure of a galaxy.

What is a galaxy? What types of galaxies are known? What does a galaxy consist of?

Proceduremdf5cb51c837bab62_1528446435040_0Procedure

The teacher discusses with students Hubble’s law.

RedshiftredshiftRedshift phenomenon:

Redshift describes how the observed light spectra are shifted towards longer wavelengths (red part of visible light spectrum) as an object in space moves further away from the observer.

This phenomenonphenomenonphenomenon allowed to find out that the Universe expands.

The redshift of an object is measured by studying the absorption or emission lines in its spectrum. The spectrum lines are unique for every element and correspond always to the same wavelengths (frequencies). When an object moves in space toward or away from its observer, the spectrum lines can be found in different position, as they were expected.

If the space between galaxies expands, the wavelength of the light sent from one galaxy stretches proportionally to the time that it needs to reach the other galaxy. RedshiftredshiftRedshift (z) is defined as the change in the wavelength of the observed light divided by the wavelength that the light would have if the source was not moving (emitted wavelength):

z=λobservedλemittedλemittedvc

where ν is the radial outward velocity of the galaxy (ν << c) and c is the speed of light.

[Interactive graphics]

Hubble’s law

In 1929 the American astronomer Edwin Hubble described the redshift phenomenon and connected it to the expansion of the Universe. The results of his observations showed that nearly all galaxies are moving away from each other. The redshift appeared to be larger for faint and, as he assumed, further galaxies. Hence, the further a galaxy, the faster it is receding from the observer.mdf5cb51c837bab62_1527752263647_0In 1929 the American astronomer Edwin Hubble described the redshift phenomenon and connected it to the expansion of the Universe. The results of his observations showed that nearly all galaxies are moving away from each other. The redshift appeared to be larger for faint and, as he assumed, further galaxies. Hence, the further a galaxy, the faster it is receding from the observer.

The Hubble’s law describes the relation between the velocity of a receding galaxy and its distance to the observer as:

v=H0·r

where v is the radial outward velocity of the galaxy, r is the distance between the galaxy and the observer and H is the proportionality constant (called Hubble constant).

The exact value of the Hubble constant is still under study. The approximate value is:

H070kmsMpc

(The latest value in 2018 from Planck Mission results is 67,66kmsMpc)

Parsec:

A parsec is a unit often used by astronomers to measure large distances to astronomical objects outside the Solar System. One parsec corresponds to the distance from the Sun to an astronomical object that has a parallax angle of one arcsecond. 1 parsec is about 3,3 light‑years. The standard abbreviation is pc.mdf5cb51c837bab62_1527752256679_0A parsec is a unit often used by astronomers to measure large distances to astronomical objects outside the Solar System. One parsec corresponds to the distance from the Sun to an astronomical object that has a parallax angle of one arcsecond. 1 parsec is about 3,3 light‑years. The standard abbreviation is pc.

The value of the Hubble constant is important to cosmologists because it can be used to estimate the age of the Universe. If we assume that the expansionexpansionexpansion of the Universe started immediately with the beginning of its existence and it continues, then the radial outward velocity of our Galaxy can be expressed as:

v=r·t

If we compare these formula with the Hubble law than the lifetimelifetimelifetime of the Universe evaluated with the Hubble constant is about 13,8 billion years.

Lesson summarymdf5cb51c837bab62_1528450119332_0Lesson summary

In 1929 the American astronomer Edwin Hubble described the redshiftredshiftredshift phenomenonphenomenonphenomenon and discovered that the Universe expands.

Selected words and expressions used in the lesson plan

escape of galaxiesescape of galaxiesescape of galaxies

redshiftredshiftredshift

expansionexpansionexpansion

phenomenonphenomenonphenomenon

Hubble’s constantHubble’s constantHubble’s constant

spectrum linespectrum linespectrum line

lifetimelifetimelifetime

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escape of galaxies1
escape of galaxies

ucieczka galaktyk

R1DuCbRCgl4rR1
wymowa w języku angielskim: escape of galaxies
expansion1
expansion

rozszerzanie

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wymowa w języku angielskim: expansion
redshift1
redshift

przesunięcie do podczerwieni

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wymowa w języku angielskim: redshift
phenomenon1
phenomenon

zjawisko

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wymowa w języku angielskim: phenomenon
lifetime1
lifetime

czas życia

R1a3WCbNgdraJ1
wymowa w języku angielskim: lifetime
Hubble’s constant1
Hubble’s constant

stała Hubble’a

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wymowa w języku angielskim: Hubble’s constant
spectrum line1
spectrum line

linia widmowa

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wymowa w języku angielskim: spectrum line