How the Parkes dish helped the world watch the first moonwalk

The whole world was watching

On Monday 21 July 1969, at 12:56 in the afternoon Australian Eastern Standard Time, astronaut Neil Armstrong stepped onto the Moon. About 600 million people, roughly one in every five people alive at the time, watched it on live television.

Armstrong and Buzz Aldrin had landed their lunar module, called Eagle, on a flat plain called the Sea of Tranquillity at 6:17 that morning. A small black-and-white TV camera on the lunar module sent pictures back to Earth as radio signals.

After travelling hundreds of thousands of kilometres through space, those signals were very faint. Catching them needed giant dish antennas. Three were listening at the same time: NASA's Goldstone station in California, the Honeysuckle Creek tracking station near Canberra, and the Parkes radio telescope in New South Wales.

A giant dish in country NSW

The Parkes radio telescope, now also known by its Wiradjuri name Murriyang, stands just outside the town of Parkes in central-west New South Wales, about 380 kilometres from Sydney. Its dish is 64 metres across, and it was officially opened on 31 October 1961.

A radio telescope does not collect light like a camera. It gathers faint radio waves from space and focuses them onto sensitive receivers. The bigger the dish, the more signal it can collect. Parkes only ever listens: it receives signals from space but never sends them.

In late 1968, NASA asked for Parkes to help with Apollo 11. Its huge dish could pull in a stronger signal than smaller antennas, so the astronauts would not need to spend precious time on the Moon setting up an extra antenna of their own. The observatory's director, John Bolton, agreed to a contract that was just one line long.

A change of plan

The original plan had the astronauts resting for several hours after landing before their moonwalk. By then the Moon would have been high in the sky over Parkes, so Parkes was expected to be the main station for the TV pictures.

But the astronauts decided to go outside early instead. That was a problem, because the Parkes dish cannot tip all the way down to the horizon. It can only point at things at least about 30 degrees above the horizon, so the Moon had to climb that high before the main receiver could see it.

Luckily for Parkes, getting ready took much longer than expected. Putting on backpacks, boots and gloves, and letting the air out of the cabin, took hours. By the time the hatch opened, the Moon was just rising into the telescope's view.

A wild and windy day

The weather at Parkes that day was miserable, with grey skies, rain and strong winds. The dish was tipped over as far as it could go, waiting for the Moon, when two sharp gusts of more than 110 kilometres an hour slammed into it. The control tower shuddered and swayed. Today, the telescope is parked pointing straight up whenever the wind is faster than 35 kilometres an hour.

The team kept calm. As the winds eased, John Bolton used a second, less sensitive receiver that could see a little lower than the main one. It picked up the TV signal just as Aldrin switched the camera on. For the whole moonwalk, the telescope worked well outside its normal safety limits.

The man steering the dish, Neil 'Fox' Mason, had to keep it pointed exactly at the Moon by watching a signal meter. He was not allowed to turn around to look at the TV pictures, in case the wind picked up again. He saw the moonwalk for the first time on the replay at home that night.

Pictures for the world

In the first few minutes of the broadcast, NASA switched between pictures from Goldstone and Honeysuckle Creek, looking for the clearest one. Armstrong's famous first step reached the world through Honeysuckle Creek's pictures.

About nine minutes in, the Moon rose into the main beam of the Parkes dish. The Parkes pictures were so much clearer that NASA switched to them and stayed with Parkes for the rest of the two-and-a-half-hour broadcast. The signals went by special links to Sydney, then on to Australian TV stations and, by satellite, to Houston for the rest of the world. Because of that long trip, Australians saw the moonwalk about 0.3 seconds before everyone else.

More than 50 years later, Murriyang is still exploring the universe. It has been upgraded so many times that it is now about 10,000 times more sensitive than when it was built, and it has discovered almost half of the more than 2,000 known pulsars. Its Apollo 11 story even inspired a film, The Dish.

📚 Words to know

Radio telescope

A telescope with a large dish that collects radio waves from space instead of light.

Receiver

Equipment that picks up radio signals so they can be turned into sound, pictures or data.

Lunar module

The small spacecraft that carried two astronauts from lunar orbit down to the Moon's surface and back up again.

Moonwalk

Time astronauts spend outside their spacecraft on the Moon's surface. NASA calls it an EVA, short for extra-vehicular activity.

Pulsar

A small, super-dense, fast-spinning dead star, about the size of a city, that sends out beams of radio waves.

🧪 Try this: build a dish that catches sound

1. Ask a friend to stand on the other side of a room and tap a pencil gently on a table, over and over.
2. Listen normally. Then cup one hand behind your ear. Does the tapping sound louder? Your hand catches extra sound and steers it into your ear, like a tiny dish.
3. Now hold a large plastic bowl just behind your ear, with its hollow side facing your friend. Tilt it slowly until the tapping sounds loudest. Pointing a dish accurately is what Fox Mason had to do for hours.
4. Try a small bowl and then a big one. Which works better? A bigger dish collects more, which is why the 64-metre Parkes dish gave the clearest pictures of the moonwalk.