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.spot the station The average diameter of the Earth is 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 10 8 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 km Our galaxy, the Milky Way, is estimated to be ly in diameter. How many times bigger is this than our solar system?

A Sense of Scale: Our Solar System Our 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 System If the ‘scaled sun’ was in this room, where would the planets be?

A Sense of Scale: Our Solar System Choose 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 Scale Through 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 ( ) = 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

Teacher notes: How big? This is a short problem for pupils to utilise their index notation skills. Calculation: Size of the Milky Way = x 9.46 x Size of the Milky Way = 1.1 x 10 5 x 9.46 x or x Size of the Milky Way = x = 1.04 x How many times bigger than our solar system = (1.04 x ) ÷ (4.50 x 10 8 ) How many times bigger than our solar system = (1.04 ÷ 4.50) x (10 18 ÷ 10 8 ) How many times bigger than our solar system = x = 2.31 x 10 9

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 System Planet sizes This 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 sunActual size of Earth Scaled size of sun=Actual size of sunx Scaled size of Earth Actual size of Earth

Teacher notes: Our Solar System Object Diameter (km) Scaled diameter (cm) Possible object to approximately represent it Sun Tricky! As a sense of size, the width/length of a classroom (as appropriate) or mobile planetarium (hemisphere) eg here – seats 60 adults.here Mercury Walnut Venus Tennis ball (6.7cm) Earth Tennis ball (6.7cm) Mars Ping Pong ball (3.8-4cm) Jupiter Fitness ball (usually 55, 65 & 75cm) Saturn Fitness ball (usually 55, 65 & 75cm) Uranus Small beach ball (30cm) Neptune Size 5 Football or netball (22cm) Having some of these objects available will help students to appreciate the sizes involved.

Teacher notes: Our Solar System Planet distances The 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 sunActual 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 System Planet 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 System Object Distance from sun (km) Scaled distance Likely place Sun 00 In the room Mercury m Other end of (a large) school or out on the school field Venus m Earth m Mars km Jupiter km Saturn km Uranus km Neptune km

Teacher notes: Our Solar System Scale 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 x Scaled distance from sun to Neptune Actual distance from sun to Neptune Scaled diameter of planet = Actual diameter of planet x Scaled distance from sun to Neptune Actual distance from sun to Neptune

Teacher notes: Our Solar System ObjectDistance from sun (km)Scaled distance (m)Scaled size (mm) Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune m 1.09

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