The pupils affectionately call it "The Cannon" and you can see why. A small child could climb inside, ready to be blasted into space.
It takes several people to manoeuvre it from the second floor store cupboard into the lift, and then carefully roll it into the playground. All on wobbly wheels that point in different directions.
But it is a labour of love, insists Graham Crawford, head of science at Liberton High School in Edinburgh. He admits the Dobsonian telescope, which is 254mm in diameter, as opposed to the more usual 70mm of domestic varieties, is "a bit of a beast" but says it never ceases to fascinate pupils.
"In winter we can take it outside straight after school and look at Jupiter and the moon," he says. "Pupils are amazed that they can glimpse another planet so easily."
It is this sense of awe and wonder that is getting so many young people hooked on astronomy. Once the preserve of the privileged few, astronomy is now capturing pupils' imaginations like never before.
Almost 270 schools offer the Edexcel GCSE in astronomy today. Numbers taking the exam - there were 2,500 candidates in 2010 across all education sectors - have doubled every three years since 2003. Many more schools offer it as an extra-curricular enrichment activity after school.
Charlie Barclay, observatory director and head of astronomy at Marlborough College, a private school in Wiltshire, has witnessed an explosion of interest among young people. When he joined the college in 1997, just six pupils took the GCSE.
Now the department consists of three teachers and more than 60 Year 10 and 11 pupils. Two hours a week are devoted to the subject, which is run as a two-year course within the curriculum.
"We have a proper research telescope here, but it is not essential," Mr Barclay says. "The wonderful thing about astronomy is that pupils can observe from their own bedroom window with nothing more than a pair of binoculars or the naked eye."
Liberton High School does not yet offer astronomy as part of the curriculum, but its two-year-old astronomy club is burgeoning. It boasts about 20 members who meet every Monday lunchtime.
But is astronomy something only wealthy independents can afford? Not necessarily. The Cannon is worth about pound;1,000 but was donated by a member of the public who could no longer fit it in his house. Other than that, the school has a couple of pound;30 "toy telescopes" donated by colleagues, plus another freebie courtesy of the Society for Popular Astronomy.
With these limited resources, the astronomy club can do extraordinary things, capturing exceptionally clear images of the moon and the Eagle Nebula, a cluster of stars.
Using what Mr Crawford refers to as the "cheapo Argos telescope", pupils can watch sun spots cross the sun on a projected image on the floor. With the bigger telescope, they can zoom in on the flag on top of Edinburgh Castle some 5km away, or the Balmoral Hotel clock, which is about 6km from the school.
"The clock always runs five minutes fast so that people going to Waverley station are not late," Mr Crawford says. "The pupils always compare that with the school clocks to make sure they are running on time."
Once they have honed their target practice skills here on Earth, they are better able to locate minute changes in the night sky or craters on the moon.
"Moonsaics" - a mosaic of about 30 lunar observations that pupils piece together to create a large map of the moon - are provided by the National Schools' Observatory and encourage them to scrutinise every detail of its surface. Pupils also enjoy making their own spectroscopes out of old CDs and cardboard, allowing them to see the dark lines of hydrogen and helium in the projected rainbow patterns.
"Pupils are prepared to give up their own time because they love it," Mr Crawford says. "They can do it themselves, in real time, day or night, straight from the classroom. It hooks them into learning."
Even schools without their own equipment can access a wealth of free resources, computer software and events. The remote-controlled Faulkes Telescopes in Hawaii and Australia, National Schools' Observatory telescopes and Bradford Robotic Telescope are all available to pupils, who can control the powerful instruments live over the internet - taking pictures across the UK and the world.
"These days pupils can easily track an asteroid in space, monitor a recently discovered supernova explosion, or make their own colour images of galaxies and nebulae," says David Bowdley, education officer for the National Schools' Observatory, which offers young people access to professional telescopes worldwide.
"It is very inspirational. Children soon realise that what goes on `up there' in space has a direct impact on their lives on the ground," says Mr Bowdley.
The topic naturally feeds into the three sciences, design and technology and art, but it need not stop there. A week-long event last June linked astronomy with literacy to boost boys' writing skills. The free Go Cosmic project, held at The Dome in Buxton, attracted 1,000 key stage 2 and 3 pupils from across Derbyshire.
In the mornings there were presentations from five names in the world of astrophysics, including Professor Alexander Martynov, an expert in ballistics and space exploration. He shared his experiences of preparing Russian astronauts for space travel in the 1980s and 90s, and talked to pupils about a planned manned mission to Mars in 2035.
Pupils were also treated to performances from Explorer Dome, a company that uses an inflatable planetarium to surround the audience with the Northern Hemisphere night sky. Workshops on everything from Galileo to space invasions went on to inspire creative writing.
"Astronomy is a sexy subject," says Dresina Shewbridge, an astronomy presenter in schools. "Everyone is excited by it. I'm always drowning in questions by the end of a presentation."
Carl Metcalf, head of physics at Queen Elizabeth's Grammar School in Ashbourne, Derbyshire, has seen for himself how the subject captures pupils' imaginations. "Someone once said that the only parts of science that are guaranteed to excite the young are dinosaurs and space," he says. "And the dinosaurs are all gone."
"I suspect increased media coverage of genuinely exciting astronomy discoveries and space missions have helped to increase astronomy's popularity," says Robert Massey from the Royal Astronomical Society. "Meteor showers and eclipses that the public can enjoy for themselves have also helped."
Part of the appeal comes down to greater accessibility. In the International Year of Astronomy in 2009, telescopes went to 1,000 schools across the country. With their help, pupils were able to do genuine scientific research from their own classroom, obtaining raw data from celestial objects and processing them into professional images.
From a standing start about a year ago, Queen Elizabeth is now sprinting ahead with astronomy-related opportunities. Having attended the Go Cosmic event, which it used to inspire its gifted and talented Year 9 science pupils, it has set up a rocketry club in partnership with a local astronomy society.
The club invites eminent guest speakers to the school, including Professor Martynov, and plans to introduce outreach work to its primary feeder schools and neighbouring secondaries.
This summer, 50 pupils will go on a week-long masterclass to Korolyov, the epicentre of Russian space exploration, plus Star City, where Russian astronauts live and train. Up to 85 pupils have expressed an interest in the trip.
"The initiatives we have run have brought a real buzz to the STEM (science, technology, engineering and mathematics) subjects in school," says Mr Metcalf, who is looking to adapt some key stage 3 topics such as light and sound to be taught with a space theme, as well as developing a possible BTEC assignment.
"When you ask pupils what they want to learn about, over and over again they return to questions on space, because they have a thirst to know about the universe, what is out there and how they fit into it all."
At Ironville and Codnor Park Primary in Nottingham, astronomy has widened pupils' appreciation of science and nature.
"When the stars come out it is as if everything in time and space is visible in your mind - from ancient evolution through to 21st-century satellites hurtling to infinity," says Jodi Storer, 11, who won a special commendation in the Go Cosmic writing competition.
This philosophical angle to astronomy should not be overlooked, says Mick Ennis, a literacy support co-ordinator at Ironville and Codnor. Essential questions about what humans are doing here on Earth and our significance as particles in a huge cosmos, stimulate pupils to reconsider their whole concept of reality and life itself.
"It has unlocked the door to self-realisation," he says. So many great thinkers, from Galileo to Copernicus, Einstein, Stephen Hawking and Issac Asimov have grappled with these questions.
More recently, it was the turn of Professor Brian Cox, a particle physicist and TV science heart throb, and comedian Dara O Briain. They hosted three days of live stargazing on the BBC in January, featuring epic images from observatories around the globe.
It will be another small step in the attempt to enthuse pupils - not just in astronomy but in its related subjects as well. A recent survey by the UK Young Scientists and Engineers Fair found that two-thirds of parents hold back from encouraging their offspring to think about science as a career because they lack knowledge of the subject.
Astronomy is the glue that can bring all these subjects together and make them relevant, argues David Bowdley. "It brings all the seemingly isolated topics together under one storyline," he says. "The universe is one big science experiment going on around us."
And thanks to a growing astronomy movement in schools, more and more people are taking part.
The Royal Astronomical Society is launching the Patrick Moore Medal to recognise outstanding teachers of astronomy. See www.ras.org.uk
BRING SPACE AGE INTO SCHOOL