The Scruffy Astronomer

The imaginary point As we all know, the Earth rotates on its axis. This is why we see the sun rising and setting, as well as the stars moving through the night. But this gives astronomers a challenge. If you have an equatorial mount, it has to be parallel to the Earth's rotation. The more accurate the alignment, the better the mount will perform. Once aligned, you only have to move one axis has to follow a star accurately. The other one can stay still. If the mount is poorly aligned, you'll have to adjust the declination axis occasionally. Of course, this isn't a problem for visual observing. But for photography, a small polar error will ruin your photos. How can you get an accurate alignment? Geometry! I use a computer program called SharpCap to help with my polar aligning. This needs a computer and a camera on the scope. A PoleMaster does pretty much the same thing. SharpCap is very clever. It takes a photo of the polar area, you rotate the RA axis and it take...

We all remember the debate about whether Pluto was a planet. The IAU came up with some rules that defined what we call a planet or not. According to these rules, Pluto is a "dwarf planet", or possibly a Kuiper Belt Object (KBO) Object. My recollection of these rules was that one stated that for an object to be a planet, it must have cleared out its orbit, dragging them into its gravity well. Pluto failed this definition due to other KBOs such as Orcus and Albion. But Venus has a dust ring - not a ring around the planet like Saturn and Uranus have, but an agglomeration of dust all along its orbit - it looks like a donut around the Sun. We've known about this ring for a little while - it has been observed by a couple of other instruments in orbit, but it's now been photographed by the Parker Solar Probe. The photo puzzled me. " a planet clears out its orbit " Does it? How could Venus have a dust ring and not violate this definition? I went ba...

Moons are, we think, very common. After all, every single planet that humans have lived on has had at least one moon. Most of the planets in our solar system have at least one moon, and some large planets have lots. By extension, why shouldn't we expect that exoplanets would also have moons? But how do we find them? There are a few methods. I'll try to explain the "transit" method for exomoon detection here, although there are others. Scientists record the amount of light coming from a star. A dip in the luminosity may indicate the transit of an exoplanet. By extension, higher-resolution measurements may be able to detect the transit of an exoplanet with a moon, but it would depend on the arrangement of star, planet and moon to be just right. Have a look at the sequence in the graphic above, and my scribbled light trace over time. In the first panel, the planet and moon are approaching transit. Here the luminosity would still be 100% of normal. ...

I was talking about wide-field images with a customer last year. Mal showed me a photo he'd taken while back "up north". He'd used a now-elderly Canon M3 mirrorless with a Samyang 2.8mm fisheye. Mal told me that when he took this photo, he was in an area so dark that he hadn't noticed he was underneath a powerline until he previewed the photos on the back of the camera. You can see the lines go through the Small Magellanic Cloud. We both agreed that we enjoyed working in the dark. The bluish colour on the horizon is a car on a main road. That power pole provides a subject for the centre foreground. Without it, these photos get boring - just fields of stars. The shot was less than 30 seconds at f/2.8. He'd set the ISO very high. The camera has a clever noise reduction system, which takes three "light frames" and one "dark". Noise measured in the dark frame is subtracted from the lights, which are then stacked, further reducing ...

Back in December 2018, I wrote about the trinary star system of Alpha Centauri (see photo). The star you can't see, Alpha Centauri C, is a bit overlooked, even though it's the closest star to the Earth (apart from the Sun, of course). It's more commonly known as Proxima Centauri. A few years ago, scientists found evidence for a planet orbiting Proxima. They think it's about earth-sized, and in an orbit that would support liquid water. Planets are typically named after the star they orbit. The star itself is given the suffix "a", and so the first planet discovered has been named Proxima Centauri b. Of course, if Proxima is more properly called Alpha Centauri C, then shouldn't the planet really be called Alpha Centauri C a? All that aside, researchers now have evidence that there may be a second planet in orbit around Proxima. We'll call this Proxima Centauri c. There are a few ways of finding exoplanets. A lot are discovered using changes in luminance r...

  What, apart from a popular way of describing English people, is eccentricity? In astrophysics, it describes how flat orbits are. This includes orbits of planets, satellites, comets and even things that don't come back, such as Oumuamua. Most people will tell you that planets orbit around the Sun in a circle. It's close. The Greek astronomer Ptolemy certainly thought so. But, by about the 15th Century, astronomers (mainly led by the Arabic schools) had realised there was something not quite right with circular orbits. It fell to an observer and a mathematician to figure it out. Tycho Brahe - the Great Dane - was the observer. He built a series of machines, some of which were enormous. These made exquisitely precise measurements of the positions of the planets in relation to the stars. The maths genius was Johannes Kepler, who was Tycho's student. Kepler knew there was something screwy about Mars - it was never in quite the "right" position. But Tycho wouldn't...

But is it an existential threat? If you’re the anxious type, maybe you’re best not reading this… Image: NASA One of my favourite podcasters is John Green, who is known for his anxieties. He’s able to list and discuss the top 10 existential threats for humans. The other day he talked about one I hadn’t heard of before. A Gamma Ray Burst is (we think) the biggest bang in the universe. It takes the form of a focused blast of gamma rays, which are especially high energy particles. Humans only discovered GRBs when the US launched a satellite in the 1960s to monitor for Soviet nuclear tests. There are two types of GRB, neither one of which you’d like to be near, and both of which result in the creation of a black hole. The collapse of a huge star during a supernova can cause a “long” burst, of “up to a minute”. In this minute, the energy blasted into space is – get this – roughly the same as the energy our sun gives off in its entire lifetime . In January last year, NASA detected a ...

Paul is one of my oldest friends. I was at school with him back in the 1970s. Paul is the lean-in type who has never done anything in a half measure, and is now an accomplished wildlife photographer. Like me, Paul has an interest in astronomy, and has always been fascinated with the idea of photographing the Horsehead Nebula. In order to do this, he got himself a telescope. Showing that lean-in personality again, it's a Celestron 1100 EdgeHD Scmidt-Cassegrain, mounted on a CGEM-II equatorial mount. This is a big scope, and big scopes have complications, as we found. The camera he used is a Nikon D810a, which is specifically for astrophotography, having the built-in IR filter modified to allow longer wavelengths to the sensor. This is important for the Horsehead as it's in a region rich in hydrogen, which emits light at this wavelength. Last week, I went with Paul and his wife Ruth (also a photographer) to the ASV's dark sky site. This was the scope's first...

You’ve probably heard in the mainstream media that there’s a star in Orion that’s gone dim over the last couple of months and might "go supernova". Maybe, but don’t hold your breath. Betelgeuse is a red giant star in the constellation of Orion, one of the shoulders of the Hunter. Of course, in the Southern Hemisphere, we see it "upside down", so Betelgeuse is the lowest bright star in the constellation. Just now, from Southern Australia, Orion is rising in the East after sunset. A red giant is a huge star. If it were transferred to where our sun is, the Earth would be inside the star itself. So would Mars and – nearly – Jupiter. Only large stars can result in supernovas, but this one is plenty big enough. It’s also true that it’s gone suddenly and significantly dimmer over the past few months. Betelgeuse was until recently one of the top 10 brightest stars in the sky. Now it’d struggle to make the top 20 list. However, it's also variable, changing brig...

11 December 2019  There’s a comet around, although it’s a bit hard to see. I’m often a bit skeptical when it comes to comets. You hear that there’s one coming, and that astronomers hope it’ll be bright, but so often, particularly in the city, you see a dull fuzzy blob that may just as well be a smear on your lens. So, I’m always trying to manage expectations down, not up. Comet 2I/Borisov approached the solar system from the North, crossing the equator a few months back. Its closest pass to the Earth is on the 28th of December. As to brightness, it's been dim so far, but there’s the possibility of an outbreak of gas as the comet warms close to the Sun. Experts guess it might get as bright as magnitude 15. That’s not bright. You’ll need a big aperture - something like a 10-inch Dobsonian (www.opticscentral.com.au/saxon-10-inch-dobsonian-telescope.html) to see that. The interesting thing about Borisov is that it’s an interstellar comet. In fact, Borisov is only the se...

18 October 2019 The other day I read on the ABC website that our Milky Way galaxy is likely to be “eaten” by Andromeda . If there’s one thing I can’t stand, it’s clickbait. No, we’re not all about to die. First, it’s not expected to happen for another 4.5 billion years. So I wouldn’t be too fussed about it if I were you. Second, galaxies might look pretty substantial, but honestly, they’re not. Probably the most crowded place I can think of in the current universe would be a globular cluster, such as Omega Centauri (this is my shot). To give you an idea of how crowded these places are, Alpha Centauri, the closest star to the Earth, is about four light years away. The stars in a cluster like this are about one light year apart on average. Of course, in the densest part, they’re much closer - down to one light day apart. Life as we know it (Jim) in there just wouldn’t be possible. Star collisions here are a genuine possibility. Not only that, any planet would be torn away from ...

This was originally five separate Facebook posts. It's been republished by the Astronomical Society of Victoria and in a couple of other places as well. Although I think it was originally a pile of notes that got saved after my university course in History and Philosophy of Science from the mid 1980s. 1: Introduction 4 October 2019 What happens when objective observation comes up against hubris? Hubris wins. At first. I'm going to spin out a yarn. It's quite a good one, about how humans figured out how the planets move through the sky. It also shows a lot about how humans began asking the big questions: of "what?" and more importantly "why?" That humans ask themselves these questions about pretty much everything is, I think, the thing that sets us apart. That these questions are unanswerable doesn't matter - it's a goal that drives our understanding, not only of astronomy, but in fields as diverse as psychology and economics. But it...

Detection of aliens is fine, but is it a good idea to communicate? We've got a new way of detecting what may be alien communications - light pulses. Humans have been listening to radio frequencies for about 100 years now. This really isn't a great length of time when you're talking about interstellar communications. The Milky Way galaxy is about 100,000 light years across, so those first signals broadcast by Marconi have travelled only about 0.1 percent of the width of our own galaxy! Of course, listening is a different matter. Alien civilizations, if they're out there, may have been broadcasting for thousands, or hundreds of thousands of years, so we could detect them from much further away, even from the far side of the galaxy. But have we been wrong to look only at radio transmissions? Breakthrough Listen, a group founded in 2015 to search for signs of alien life, has begun watching for short flashes of light - something they call "pulsed optical beaco...

30 January 2019 A planet-sized game of pool? It reminds me of Red Dwarf episode, but that's how Earth got a lot of its elements. I was talking with a customer the other day about water on Earth. We both found it mind-boggling that most of our water came from space in the form of harmless comet collisions. The majority of comets are cricket-ball sized "dirty snowballs". When they hit our atmosphere they turn to steam, and fall as rain. But what about the other stuff? Over 4 billion years back, our newly-formed Sun was creating a giant disc of dust and garbage gathered from previous supernovas in the area. Astronomers call this a proto-planetary disc. They've seen it happening around other new stars as well well - this photo is from a system called HL Tauri. In this disc, elements were gathering in bands at different distances from the centre. It's really an astronomical-sized centrifuge. As planets formed in the disc, they started off with just the elemen...