Doug Daniels with the telescope at the bottom of his garden
The Hampstead Scientific Society is celebrating the 100th anniversary of its observatory, one of the few in London that regularly opens to the public.
The society's president, Doug Daniels, 70, has been a keen amateur astronomer since he was 13.
To whet the appetite for the BBC's Stargazing LIVE event, Mr Daniels talks about making your own telescopes, how the skies have changed and why the Icelandic volcano was such good news for astronomers in London.
How did you get into astronomy?
I was at grammar school in east London and on one particular day in March 1953, a terrific thunderstorm broke and we were told not to go to the sports ground but to the library instead.
I reached up into the bookshelf and removed a book called 'Observing the Heavens' by Peter Hood and it showed you how to make a simple telescope.
I was immediately enthralled. I found an old spectacle lens, a cardboard tube and a microscope eyepiece. I took it outside on the first clear night and looked at the moon.
I was amazed that I could see the craters on the moon. Then I saw a bright star and noticed that it was a tiny little disc and to the side of it were four little dots. I realised I was looking at Jupiter and its four major satellites.
From then on I was hooked and went on to build bigger and bigger telescopes.
What advice do you have for young people who want to learn more about astronomy?
Professor Brian Cox and Dara O Briain are bringing the wonders of the stars to BBC2 between 3-5 January 2011.
Stargazing LIVE will reveal images from the most powerful telescopes on Earth, and beyond, during three nights of extraordinary astronomical events.
It's less cost-effective now because there are so many telescopes available. When I first started the only sort of telescopes you could get were antique Victorian objects made of brass - beautiful pieces of instrumentation but they cost a fortune.
I would say if you are getting into astronomy now, the best way to start is a good pair of binoculars and a simple star map. Learn the constellations because, let's face it, you can buy a telescope with a built in computer and once you've set it up will automatically point in the direction that you've dialled in.
That's not the way to do it. You have to look at the sky and learn the sky.
However, there is nothing quite so satisfying as taking a piece of glass, grinding it to a perfect figure, mounting it on a tube, pointing it at the sky and looking it at these objects with an instrument you've made yourself.
Do people still have that sense of wonder about the skies?
I think so. It can lead to a certain disappointment when they look through a telescope for the first time and they'll expect to see volcanoes on Mars and that sort of thing.
Anyone who has ever looked through a telescope for the first time and looked at Saturn with its wonderful series of rings cannot fail to look at that without gasping in admiration and saying how wonderful and how artificial it looks.
It is the one thing that lives up to the pictures in books.
Most of the other things you see in magazines and books are taken with long-exposure photography and you can't see them with the naked eye.
How has it changed since you first started?
Light pollution is the main problem. I've seen a steady decline over 45 years.
The government need to lead by example and one way they could do this is to re-design street lighting and stop illuminating public buildings at night.
There is also massive pollution from aircraft contrails. Aircraft pump thousands of tonnes of carbon dioxide directly into the upper atmosphere and they can actually affect local weather conditions.
When the volcano in Iceland erupted we had a series of clear nights when aircraft were on the ground and we noticed a distinct improvement in the atmospheric quality.
London is at a disadvantage because you can no longer see the glories of the night sky. Every year I get people coming to me after they've been on holiday to somewhere like Crete. They have experienced for the first time a perfectly clear night sky and they've been awestruck by what they've seen.
What is the Hampstead Scientific Society?
I joined the HSS in 1965. The society started in 1898 and is a general scientific society; we hold regular monthly lectures on all branches of science and technology but it has always had a very strong astronomical section based on the Hampstead Observatory based at Lower Terrace.
The Hampstead Observatory has been open to the public since 1910
The Observatory as it stands today was established in 1910 so we are celebrating our centenary year. It has always been our brief to allow access to this instrument to the public.
We've also got a Met station up there that was formed at the same time as the observatory and we have just received an award for being the only Met station in the country that has supplied continuous daily observations from one site for 100 years and we are very proud of that fact.
Do you have a favourite astronomical experience?
I can tell you of the most profound experiences that I've had.
When I was at school we went on a school trip to France and we did the crossing from Southampton to St Malo at night and in the middle of the channel, which fortunately at that time was absolutely flat, I went up on deck and looked at the sky and I still feel goose bumps now when I think of that experience because it was absolutely jet black.
The Milky Way was like a pale river of light arching across the sky and there were so many stars visible that you found it difficult to pick out the familiar constellations.
You realised that ancient mariners must have seen this on a regular basis and you could actually appreciate that you were on a planet, in a universe of absolute majestic beauty and it took your breath away.