Losing Pluto

When I was a science teacher , the national Curriculum for Science insisted that there were 9 planets in our solar system and that they had an ordr from the Sun, and that children needed to know and retain that fact. We came up with crazy rhymes to lean , like :

My Very Easy Method Just Set Up Nine Planets

Many Vile Earthlings Munch Jam Sandwiches Under Newspaper Piles,

even encouraging children to make up their own ideas.

These nmnemonics, where the first letters of each word represented the first letter of each planet,  namely Mercury, Venus, Earth, Mars; Jupiter Saturn Neptune and Pluto.

Around the 2000’s , rumours started out that Pluto was for the chop. It wasn’t the first time a “planet” had been culled from the list, as Ceres was considered a planet and then in 1850, it was given the chop. Today, It is considered a “dwarf planet”

Well all this got me wondering. What is a planet? How do we know the difference between Ceres or Pluto or Earth, or even our Moon? a quick glnce at Wikipedia and hey presto the knowledge is aquired. it seems that planets have a big enough mass for gravity to pull them into a spherical (or near spherical) shape. Ok, that’s easy to understand. It also has to have a big enough gravity to have cleared the zone of other bodies, (so there shouldn’t be an asteroid field in the orbit, for example) .So Pluto gets culled on this point, as does Ceres. And for pluto, another dwarf planet, Eris ,was found in 2005 which was bigger than Pluto. At first they said 10 planets, then they got together and decided that they would intorduce the term dwarf planet.

Anyway, since then, the UK govenrment changed the Key Stage 3 guidance to make it much less prescriptive and today it looks like this

Students must know:


Space physics

gravity force, weight = mass x gravitational field strength (g), on Earth g=10 N/kg, different on other planets and stars; gravity forces between Earth and Moon, and between Earth and Sun (qualitative only)

our Sun as a star, other stars in our galaxy, other galaxies

the seasons and the Earth’s tilt, day length at different times of year, in different hemispheres

the light year as a unit of astronomical distance.


So what happened to Pluto, I hear you ask.Well he lives with Micky and his friends!

No really, its a dwarf planet out in the far reaches of cold space. And students don’t need to know the names of the planets or their order anymore.



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