The Scruffy Astronomer

31 December 2018 How well do you know your neighbours? Alpha Centauri (Rigil Kentaurus, or just Rigel Kent) is not just a single star. It’s not even a double, it’s probably a triple. Alpha Centauri A and B appear as two stars very close to each other in a telescope. You have to have a scope with a long focal length to be able to split the two. When I was a kid, we used to judge how good people’s scopes were by looking at Alpha Centauri to see if the scope could split the binary pair. To do it, the scope needed a lot of light gathering ability, good optics, and a long focal length. That probably also suggests a lot about what I was like as a kid. The distance between these two stars is only about 11 times the distance between the Earth and the Sun. The pair dance with each other, taking about 80 years to complete a do-si-do. Any planets nearby would be well cooked. Their poor neighbour, Alpha Centauri C, is dull red, nearly invisible and also about 0.2 light ye

28 December 2018 It's intimidating, sure, but there are people to help, and it doesn't need to be expensive. Bill's written a blog post about how he got started, including some of his early photos. He discusses some of the choices that beginner astrophotographers face, as well as a couple of pitfalls to avoid, and (importantly) how to avoid spending lots of cash up front.

26 December 2018 Have you seen the Lunar X?   This is a light effect that happens on the Moon at the most once each month. However, due to the Sun's position as well as the Earth's spin, it's only seen from any particular part of the Earth a few times each year. Bill's latest blog shows his photos of it , how to see it, how to photograph it, and when it's going to be visible from Melbourne during 2019. You can also watch a video on the Optics Central's YouTube channel.

25 December 2018 Today is the 50th anniversary of this, one of the most famous photos of all time. Earthrise, taken by Bill Anders, one of the astronauts on Apollo 8 has come to represent how alone humanity is, as well as how dependent we are on a single planet. The photo was taken on the 24th of December 1968 with a Hasselblad 500EL/M camera with a roll of 70mm Kodak colour film. Merry Christmas to all our customers and friends! Photo: William Anders / NASA

24 December 2019 Rainbows happen when the white light from the Sun is refracted by raindrops in the air, a bit like the triangular prism on the front of the Dark Side of the Moon album. But what happens if the sun is very close to setting, and the dust and atmosphere has blocked out all the blue end of the spectrum, giving the red colour of a sunset? Well, this happens. The light that does hit the raindrops gets refracted, but there's no green or blue in the rainbow.   In telescopes and binoculars, this refraction is undesirable, and called chromatic aberration. Doublet and triplet refractor telescopes have specially designed lenses that counter this.

21 December 2018 Astronomers at the Minor Planet Center at Harvard University have discovered another minor planet way (and I mean WAAAY) out in the solar system. Perhaps not surprisingly, they've nicknamed it "Farout", but its official name is the rather unromantic 2018 VG18. It was discovered (and then confirmed) photographically. Two photos Were taken of the same area of the sky at different times and then compared. The photos are below, with Farout marked with the green arrows. Notice how it's moved a bit? Farout does move very slowly, taking about 1000 earth years to complete an orbit or the sun. Astronomers hope that by watching Farout and learning more detail about its path, they'll get closer to finding the mysterious Planet X, which they are pretty certain is out there somewhere. I took a similar pair of photos of Uranus a couple of months ago, including its two major moons, Oberon and Titania. It doesn't need a very big telescope, b

17 December 2018 For those of you who are up early and looking east, Venus is now moving away from the Sun and will be very bright over the next few weeks, rising before dawn. On 4 December it was very close to the nearly-new Moon, which looked very photogenic. But you haven't missed out! On 2 January 2019 it'll happen again, only Jupiter will be also joining the parade. Then on 23 January, Venus and Jupiter will be right next to each other in the morning sky, both just adjacent to Scorpio as it rises. On 1 February Venus will be even closer to the razor-thin moon - only two moon widths. That'll be a magnet for the photographers! This is the only photo I've ever taken of Venus. At the time all I could say was that it was about the right shape. To get a good look at it, you're going to need a pretty long focal length, say better than 1500mm. For this type of job, nothing is really better than the Cassegrain or its variant, the Maksutov. What's the

8 December 2018 Did you know that most meteor showers happen at the same time each year? The Geminid meteor shower is due to peak next weekend. Dust left behind by an ancient asteroid called 3200 Phaethon hangs around in a smallish spot in the Earth's orbit. Because we travel through this part of the orbit at the same time each year, we move through the cloud and pick up bits of dust. Are you planning to look out for meteors? It's best to look after midnight, and look towards the constellation Gemini, which will be low in the north east. Keep a special lookout for meteors that travel upwards! Photo: NASA

Just how did OSIRIS-REx get to Bennu anyway? OSIRIS-REx is the name of one of NASA's interplanetary probes. It's just edging towards a skyscraper-sized asteroid called Bennu right now. Apart from the composition of the asteroid, its "potentially Earth hazardous" orbit makes it of some, er, shall we say, "interest"? Bennu's orbit is not terribly much bigger than Earth's, but it is way more egg-shaped. For some of its time, Bennu is closer to the Sun than the Earth, but for the rest of the time it's further out. This means the orbits come very close about once every six years or so. Who else out there has played Kerbal Space Program? I have to say, this is by far my favourite computer game - if it can be called a game. Suffice to say that everything I know about orbital dynamics I learned from Kerbal. To get from one orbit to another, NASA engineers had to do a very complicated dance with OSIRIS-REx. It had to take off, pull away from Earth, m

24 November 2018 Tawny Frogmouths are nesting at the moment. Tawnies (which are part of the Nightjar family) are probably more common than you might think, because they're so good at camouflage that in the right tree, they look just like a stick, especially as they tend to sit absolutely still with their beaks in the air. Their call is pretty strange for a bird. It's a droning "woo-woo-woo" sound. Here is recording of one that Nick Talbot has uploaded to the Xeno-Canto website. http://www.xeno-canto.org/352950 The adult that lives down our street has developed a nifty feeding technique. She perches on a telephone pole one down the street from a street light, and then flies past the streetlight through the cloud of moths that the light attracts, then perches on the next pole down. She'll fly up and down the street all night, snaffling moths all the while.

23 November 2018 There's a comet coming! 46P/Wirtanen will be here in December (although it's already visible if you're clever). It'll sweep past Earth quite close, passing closest on the 16th of December, and at that time it'll be very photogenic in the late evening, coming right between the Pleiades and the star Aldebaran. This photo is my shot of Halley from 1986. I blogged about it at http://www.opticscentral.com.au/blog/comet-wirtanen-is-coming-back-again/

21 November 2019 NASA’s InSight lander is approaching Mars, and is scheduled to land on 26 November. This is no small feat, as if it doesn’t slow down from its current 5.5 kilometres per second (that’s about 20,000 kph!), the lander will end up a dirty smear in Mars’ deserts. It’ll use three different ways to slow down: a heat shield while it blasts through the upper atmosphere, a huge parachute, and finally a “sky crane”, which is a bank of 12 retro engines to land gently on the surface. Hopefully. Once these challenges are over, the science will begin on Elysium Planitia. Keep up with all this in real time on NASA’s live broadcast, and for more information, check out NASA’s mission page.

19 November 2018 Eastern Koels are back in Melbourne! For the last couple of years at about this time, Koels have begun to make their presence felt. Other Australians, particularly down the eastern seaboard, have been swearing at this bird for years. A Koel calls loudly overnight, making it both recognisable and unloved. They’re also unpopular with other birds, as it’s a type of cuckoo, and will lay eggs in other birds’ nests. Somewhat sadly, the other birds aren’t sufficiently intelligent to tell the difference between their own eggs and the Koel eggs, so once they’re laid, the host birds end up raising the Koel chicks. https://www.birdsinbackyards.net/species/Eudynamys-orientalis Photo credit: Geoffrey Dabb