Sutherland Astronomical Society will hold two open nights at Green Point Observatory to mark the 50th anniversary of the moon landing.
The public will be able to use the observatory's large telescopes to see the crater where Apollo 11 landed on July 20, 1969, before Neil Armstrong set foot on the moon six hours later on July 21.
The observatory's open nights will take place three weeks later on Friday and Saturday, August 9-10, when there will be a great view of the moon.
"July 21 is near last quarter moon, which means it won't be rising until late at night," the society's president Craig Goulden said.
"We have timed the open nights to be near first quarter moon because the line between night and day, called the terminator, affords the most stunning views of craters and mountains.
"This is because this line is where the sun is rising on the moon, so similarly to earth sunrise, the sun is casting long shadows across the terrain.
"We will be able to see the Apollo landing sites that are on the day side of the moon and, most importantly, the landing site for Apollo 11.
"Of course, no telescope on earth is large enough to see the lunar lander itself because it is so small and so far away, about 400,000km.
"All the Apollo sites have, however, been photographed by satellites orbiting the moon."
Mr Goulden said visitors to the observatory would also be able to see Jupiter, Saturn, star clusters and nebulae, where stars are born.
"We will have a great view of Jupiter and Saturn," he said.
"On the Friday night, the moon will be approaching Jupiter, and on the Saturday night the moon will have passed Jupiter on its eastward march and will be approaching Saturn.
"The moon, Jupiter and Saturn will be joined by the bright star Antares, the heart of Scorpius the scorpion, in what astronomers call a 'conjunction', where objects in the sky appear to be close together."
Operating in the observatory dome will be the huge, 41 centimetre Selby Newtonian telescope, which is 2.5 metres long.
It was built over 50 years ago by club members, upgraded over the years and is now fully computer controlled.
The roll-off roof observatory also houses a 35 centimetre Schmitt Cassegrain telescope, which is normally used for astrophotography and spectroscopy, but will be available for visual observing on the open nights.
On the field adjacent to the observatory, society members will make about a dozen of their own telescopes available.
"They will afford excellent views of a range of astronomical objects, but the queues will be shorter than for the observatory telescopes, Mr Goulden said.
"The field is the best place to have conversations with the telescope operators, who love talking about astronomy and telescopes, and can answer any questions you may have.
"We will be presenting astronomy lectures on various topics, and there will be a barbecue with hot and cold food and drinks. Books, posters and gifts will also be on sale.
"We recommend you bring your curiosity, questions and warm beanie.
"Standing out on the field is always colder than you might think, so it's best to come prepared."
The observatory, on the corner of Green Point Road and Caravan Head Road in Oyster Bay, will open on Friday and Saturday, August 9 and 10, from 6pm to 10pm.
Admittance is $12 for adults, $5 for children and $25 for families, paid by cash at the gate. Bookings are not required.
Visit: sasi.net.au
