The ringed planet Saturn can be seen in the north-east each evening after dusk. Tonight the gibbous Moon is below and to the right or east of the planet. We will not see the Moon cover or occult Saturn tonight; for that we need to wait until next month when there will be an occultation on the evening of Monday 4 August.
Saturn and the Moon. Chart Nick Lomb
This constellation, known as Crux to astronomers, is high in the southern sky. Five stars are visible to the unaided eye in Crux: four mark the arms of the cross and the fifth one is inside. Seeing Epsilon, the faintest star, is getting harder from brightly lit urban areas.
The Southern Cross. Photo Nick Lomb
The Christiansen’s (Left), Miller Goss (Centre), Hastings Pawsey (Right), making connections on the Birth Of Radio Astronomy Walk at Dover Heights. Photo T. Stevenson, 2014.
The ‘Birth of Radio Astronomy’ walk, held on Sunday 6 July 2014, was a great opportunity for participants to find out some of the behind-the-scenes details from Professor Miller Goss, radio astronomer and author of ‘Making Waves: the story of Ruby Payne Scott, Australian pioneer radio astronomer’ plus enjoy a morning in the sunshine at spectacular locations. Goss spent nine years in Australia and researched in radio astronomy with many of the people who were vital in developing this field, including Bruce Slee, Chris Christiansen, John Pawsey, John Bolton, Bernie Mills, Wayne Orchiston and Ron Ekers. Of particular interest to Goss is the contribution made by Ruby Payne-Scott, whose discoveries made at Dover Heights field station in the 1940s were particularly important. She was the first woman working in radio astronomy.
We started at Rodney Reserve, Dover Heights. This was the site of the first discovery of solar activity using a technique called ‘interferometry’, made on Australia Day, 1956, by Payne-Scott. Anyone can go there and see the monument and replica of one of the radio antennas by looking over the cliff-face. Payne-Scott was one of a team of radio engineers who were working under John Pawsey’s direction at the CSIR ( now called CSIRO). Hastings Pawsey, John’s son, joined us on the walk and he added to the story. His father is to be the subject of the next book which Miller Goss is co-authoring. Also on the walk was Tim Christiansen, son of Chris Christiansen an innovative and highly influential radio astronomer. Tim remembers visiting Sydney Observatory with his father and family for a night telescope viewing conducted when Harley Wood was the Director and NSW Government astronomer.
Miller Goss explains interferometry at the Radio Astronomy monument, Rodney Reserve. Photo T. Stevenson 2014
Sydney Observatory has a direct connection with early radio astronomy as it was Harley Wood, who helped identify Taurus as one of the first galaxies able to be imaged using radio technology.
Some of our group also sighted whales breaching out to sea. We then walked around to the South Head Signal Station and were given a very special guided tour by Marine Rescue NSW. This is the site of Australia’s first signalling point, dating back to 1790. We were able to go up into the Signal Station designed in 1838 by Mortimer Lewis,and added onto during the 1840s. Lewis was also the architect for the Fort Phillip Signal Station which is part of the Sydney Observatory site. It was very interesting to see the Marine Rescue volunteers in action and be able to look west to the city and clearly see Sydney Observatory and Fort Phillip Signal Station.
South Head Signal Station, designed by Mortimer Lewis, constructed 1837-1840s. Photo T. Stevenson 2014
South Head Battery, which dates back to the 1890s, was also an interesting stop on our walk. Mary Knaggs from the NSW Government Architects office has written a Conservation Management Plan for this important site well worth a read for its insight into the heritage of this area.
Our final stop was at the anchor of HMS Dunbar, wrecked just below the cliffs near The Gap in 1857. This tragic tale had a major impact on the colony and was an impetus for the colonial government to improve its lighthouses and signalling devices. Furthermore soon after the disaster NSW Government Astronomer, William Scott, ensconced at the almost-completed Sydney Observatory, hurried along with organising the astronomical and timekeeping instruments so the time ball could be regularly and accurately dropped. This was to provide a signal by which ships could accurately set the time on their chronometers and therefore navigate through treacherous coastlines more accurately.
Sydney City Skywatcher walking tour in front of the anchor from the ill-fated HMS Dunbar. Photo T.Stevenson 2014
This walk was organised by the Sydney City Skywatchers, an astronomy group who meet the first Monday of the month, 6:30pm, at Sydney Observatory. Professor Miller Goss is the guest speaker on 7 July 2014.
The red planet Mars is high in the north each evening after dusk. Tonight the gibbous Moon is to the right or east of the planet. To add extra interest to the sight we also have the bright star Spica above the Moon, while the ringed planet Saturn is to the right or east of the tight group of three.
Mars, Saturn and the Moon. Chart Nick Lomb
This morning at 10:13 am AEST the Earth was at aphelion, the furthest point in its annual journey around the Sun. At this point the distance to the Sun is 152,097,350 km, which is about 5 million km more than the distance at the closest point in January.
The path of the Earth around the Sun. Drawing Nick Lomb
Arcturus, the brightest star in the constellation of Boötes the Herdsman is prominent in the northern sky in the early evenings. It is easily recognised as it is bright and has a reddish colour. The name comes from the Greek and means the Bear-watcher or Bear-guard.
Arcturus finding chart for 3 July 2014. Chart Nick Lomb
If there was no Moon there would be no tides. Our day would be much shorter as the tides act as a brake on the Earth’s rotation. Life would be much less romantic and where would the astronauts have landed in 1969?
The gibbous Moon on 3 April 2012. Photo Nick Lomb
An artist’s concept of some of the multi-planet systems discovered by the Kepler spacecraft. Courtesy NASA
The possibility of life elsewhere in the Universe is a fascinating and much discussed subject. Here and in a subsequent post I would just like to mention a few relevant thoughts. Let us confine ourselves only to our own galaxy the Milky Way. This is because, as Douglas Adams told us, ‘space is really big’ and other galaxies are too far away and too inaccessible for us to have any hope of determining anything about whether any of them have life or not.
There are over 100 million stars in our galaxy. Thanks to extremely accurate velocity measurements using large ground-based telescopes and to the Kepler spacecraft we now know of 1500 planets confirmed to be circling around other stars. Surely, there is life on some of these planets and on some of the millions of other planets that we have not yet found!
There are issues to consider. First, what do we mean by life? Most likely planets with simple one-cell organisms are far more prevalent than those with multi-celled animals or with intelligent life able and willing to talk to us.
The only example we have of life is the one on Earth and that has developed on a rocky planet with lots of water circling around a fairly average sort of star, the Sun, which has a surface temperature of about 5500°C. It is therefore reasonable to search for life on planets of about the same size circling around similar stars.
We do not know how life arose on Earth, but it can be taken as a given that however and wherever on the planet it began a good supply of organic molecules was essential. Fortunately, space seems to be full of such molecules. Radio telescopes have detected more than 80 types of organic molecules in interstellar clouds, which will eventually form new stars, including ethyl alcohol and the amino acid glycine.
Of the 100 million plus stars in our galaxy about 10% are Sun-like stars (G and K spectral type) giving, say, 10 million stars. According to a recent article published in the Proceedings of the National Academy of Sciences USA about 1 in 5 of these stars have Earth-size planets circling in the habitable zone, that is the zone in which the temperature is right for liquid water to exist on a planet’s surface. So we have 2 million possibilities.
These kinds of considerations are incorporated in the famous Drake equation. Devised by Dr Frank Drake, the equation tries to establish the number of civilisations that we could communicate with in our galaxy. It is a very simple equation with seven terms multiplied together; the only problem with it being that some of the terms are unknown and not really knowable.
Besides factors that estimate the number of possible planets, as we have done above, there is a factor for the fraction of planets where there is intelligence or life that is interested in communicating. And the most important factor is the lifetime of any civilisation that develops. We know from history that many civilisations such as that of the ancient Egyptians, ancient Greeks and the Romans did not last and we know that humans on Earth face existential threats both on the planet itself such as global warming and from outside such as asteroid impacts. Thus there may have been civilisations on distant planets that no longer exist in our own time.
If there is a reasonable likelihood of intelligent civilisations in our galaxy we need to ask why we have not heard from them and why they have not visited the Earth. We will do so next time when we discuss the Fermi Paradox.
A pair of binoculars shows a fuzzy ball of stars above the Southern Cross and the pointer stars in the evenings. This is Omega Centauri, a globular cluster containing several million old stars. It is the most massive of the 160 or so globular clusters circling the centre of our galaxy.
A Hubble Space Telescope image of the central core of Omega Centauri. Courtesy NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
In the early morning on this day in 1908 there was a colossal explosion in a remote area of Siberia near the Tunguska River. A small asteroid about 60 metres across is believed responsible. Though the effects of the impact were noticed as far away as London, scientists did not explore the area until 1927.
Trees knocked down by the Tunguska explosion. Courtesy Leonid Kulik and Wikimedia Commons