A Sense of Scale: How fast?The International Space Station

orbits the Earth several times a day.

Information:• The ISS spot the station page will tell you when you

are able to see the station in your hometown.• The average diameter of the Earth is 12742 km.• The ISS orbits at a height of 370km.

How many times does it orbit the Earth each day?

How fast does the ISS travel?

A Sense of Scale: How big?Our Solar system is big, at 4.50 x 108 km from the sun to Neptune, but how does this compare to other distances?

A light year (ly) is the distance light travels (in vacuum) in a year. 1 ly is 9.46 x 1012 km

Our galaxy, the Milky Way, is estimated to be 110 000 ly in diameter.

How many times bigger is this than our solar system?

A Sense of Scale: Our Solar SystemOur Solar System consists of the sun

and 8 planets which orbit it.

It is often represented in diagrams (such as the one on the next slide) to convey a sense of how large or small Earth is compared to the other planets and the sun. But, how representative is this? Do we get a proper ‘sense of scale’ from it?

This activity will help you appreciate the true scale of our Solar System.

A Sense of Scale: Our Solar System The diameter of a tennis ball is 6.7cm.

Using this to represent the Earth, work out the size of the sun and the other planets in the Solar System.

Can you think of a spherical object which could be used to represent each one?

A Sense of Scale: Our Solar SystemIf the ‘scaled sun’ was in this room, where would the

planets be?

A Sense of Scale: Our Solar SystemChoose something large, such as a long corridor, the

school hall, a football pitch, netball court or a 100m running track. Measure it (if necessary).

If the sun were at one end and Neptune at the other, where would the other planets be?

How big would:

– The Earth be?

– The sun be?

Teacher notes: A Sense of ScaleThrough these activities, pupils will gain a sense of the size and distances that exist within our solar system.

There are two short ‘starter’ activities: ‘How fast?’ and ‘How big?’ and one longer activity ‘Our Solar System’, which could be split into three shorter activities. The tasks are aimed at Years 9 to 11.

It is suggested that pupils approach the longer task as a problem solving activity, working in pairs or threes.

Teacher notes: How fast?This is a short problem that pupils should find engaging, particularly if the spotter is used live.

Use the ISS spotter to find two consecutive times that the ISS is overhead.If the sighting opportunity is from 05:06 to 05:10, the sighting could be assumed to be at 05:08.

The ISS actually takes 91 minutes to orbit the Earth, but the time from one visible pass to the next can be a little longer at 95 or 96 minutes.

Calculations:

Orbits each day = 24 x 60 ÷ 91 = 15.8 orbits (will be 15 orbits if 96 minutes is used)

Distance it orbits = π x (1270 + 370 + 370) = 6315km Time = 91÷60 = 1.52 hours

Can compare this with max speed recorded for an F1 car of 370 kmh-1

Speed =6315

= 4154 kmh-1

1.52

Teacher notes: How big?This is a short problem for pupils to utilise their index notation skills.

Calculation:

Size of the Milky Way = 110 000 x 9.46 x 1012

Size of the Milky Way = 1.1 x 105 x 9.46 x 1012 or 1040600 x 1012

Size of the Milky Way = 10.406 x 1017 = 1.04 x 1018

How many times bigger than our solar system = (1.04 x 1018 ) ÷ (4.50 x 108 )

How many times bigger than our solar system = (1.04 ÷ 4.50) x (1018 ÷ 108 )

How many times bigger than our solar system = 0.2311 x 1010 = 2.31 x 109

Teacher notes: Our Solar System

Both a structured and an unstructured format are provided. • For increased challenge for pupils, simply give them ‘Our Solar System Data sheet’

and let them devise their own ways of calculating and recording.• Pupils requiring some scaffolding should be given page 1 of ‘Our Solar System’ and

then page 2 once they have completed activity 1. • Slides 4 to 6 can be used to set the initial problem and the information for planet sizes

handed out. • The second and third parts of the problem – finding the relative distances (slide 7)

and thinking about a scale model (slide 8) – could be used as extension activities or as a whole class continuation of the problem.

If a few pupils are stuck, using a whole class mini-plenary to discuss approaches to solving the problem may be helpful.

If many pupils are stuck, using an example of how to find real distances from a map may help.

Teacher notes: Our Solar SystemPlanet sizesThis activity may seem challenging to begin with, but to determine the size of the planets, pupils simply need to use ratio (although this may be problematic in itself).

Example:

Scaled size of Earth: Actual size of Earth

must be in the same ratio as

Scaled size of sun: Actual size of sun

so

Scaled size of sun=

Scaled size of Earth

Actual size of sun Actual size of Earth

Scaled size of sun = Actual size of sun xScaled size of Earth

Actual size of Earth

Teacher notes: Our Solar System

ObjectDiameter (km)

Scaled diameter (cm)

Possible object to approximately represent it

Sun 1 392 000 731.6Tricky! As a sense of size, the width/length of a classroom (as appropriate) or mobile planetarium (hemisphere) eg here – seats 60 adults.

Mercury 4 879 2.6 Walnut

Venus 12 104 6.4 Tennis ball (6.7cm)

Earth 12 742 6.7 Tennis ball (6.7cm)

Mars 6 780 3.6 Ping Pong ball (3.8-4cm)

Jupiter 139 822 73.5 Fitness ball (usually 55, 65 & 75cm)

Saturn 116 464 61.2 Fitness ball (usually 55, 65 & 75cm)

Uranus 50 724 26.7 Small beach ball (30cm)

Neptune 49 244 25.9 Size 5 Football or netball (22cm)

Having some of these objects available will help students to appreciate the sizes involved.

Teacher notes: Our Solar SystemPlanet distancesThe calculations for this activity are similar to those used in the planet sizes. To maintain comparisons with using the tennis ball as the Earth, the same scalar should be used.

Example:

Scaled size of Earth: Actual size of Earth

must be in the same ratio as

Scaled distance to the sun: Actual distance to the sun

so

Scaled distance to the sun=

Scaled size of Earth

Actual distance to the sun Actual size of Earth

Scaled distance to the sun = Actual distance to

the sun x

Scaled size of Earth

Actual size of Earth

Teacher notes: Our Solar SystemPlanet distances

Part of this activity is unique to the school location, so may need a little preparation.

To bring the distances to life, it would be helpful to have a local map to hand to gain a better sense of where the planets are – for Earth and perhaps Neptune, if no others.

It might be engaging for (some) pupils to identify which of the planets would be closest to their home.

Alternatively, using an online map which can be re-scaled is helpful; Google Earth, or similar, has a measuring tool that could be used to locate a place which is the right distance away from the school.

Teacher notes: Our Solar SystemObject Distance from sun

(km)Scaled distance Likely place

Sun 0 0 In the room

Mercury 57000000 300mOther end of (a large) school or out on the school field

Venus 108000000 568m

Earth 150000000 788m

Mars 228000000 1.2km

Jupiter 779000000 4.1km

Saturn 1430000000 7.5km

Uranus 2880000000 15.1km

Neptune 4500000000 23.7km

Teacher notes: Our Solar SystemScale model

The calculations are similar but values will depend on the ‘venue’ chosen.

For the relative planet sizes, the following should be used:

The answers on the next page are based on using a 100m running track. Markers (metre rules stuck in the ground or pupils holding them) could be placed at the correct locations – perhaps with very small items such as a grain of rice or a small sequin to represent smaller planets, perhaps a pea to represent Jupiter. The sun would be the size of a walnut.

Scaled distance from sun to planet

=Actual distance from sun to planet

xScaled distance from

sun to NeptuneActual distance from sun to Neptune

Scaled diameter of planet

=Actual diameter of planet

xScaled distance from sun to

NeptuneActual distance from sun to Neptune

Teacher notes: Our Solar System

Object Distance from sun (km) Scaled distance (m) Scaled size (mm)

Sun 0 030.9

Mercury 570000001.27 0.11

Venus 108000000 2.40 0.27

Earth 1500000003.33 0.28

Mars 228000000 5.07 0.15

Jupiter 77900000017.31 3.11

Saturn 143000000031.78 2.59

Uranus 288000000064.00 1.13

Neptune 4500000000 100m1.09

AcknowledgementsSolar system image: original copyright NASA, accessed http://nineplanets.org/ 2/1/14