The Scruffy Astronomer

This blog was posted (slightly edited) as an article in Crux, the Magazine of the Astronomical Society of Victoria, vol.39 no.2 April 2021. Our neighbours the asteroids Asteroids are pretty much everywhere in our solar system. Typically, they have highly elongated orbits, meaning they can cross the orbits of the planets, as the planets have much less eccentric (that is, nearly circular) orbits. There are several classes of asteroid, determined by the amount if time they spend inside or outside Earth's orbit. Atira - spend their entire time inside the Earth's orbit Aten - cross Earth's orbit but spend the majority of time nearer to the Sun Apollo - cross Earth's orbit but spend the majority of time further out than the Sun Amor - spend their entire time outside Earth's orbit Most of the Atira and Amor classes are quite safe, although some of them can approach Earth's orbit closely. However, the Aten and Apollo types don't only approach, ...

Never heard of it 99942 Apophis is an asteroid whose orbit - somewhat worryingly - intersects the Earth's. It's defined as a hazardous object. Apophis orbits nine times for every eight Earth orbits, and because of where the intersection is located, the danger period is every eighth April. Wait, what? The intersection is on the ascending node, meaning Apophis approaches the Earth from "below" (assuming Earth's northern hemisphere is "up"). This means Apophis is visible from the Southern Hemisphere before the encounter, and it falls below the horizon, becoming visible from the Northern Hemisphere after the encounter. There's a super close (but safe) pass coming up in April 2029, meaning about now is the last encounter before then. So of course I want a photo In preparation for writing an article about the asteroid, I wanted to actually get a photo of it. Because it's not a very close pass, it wanders by rather than zooms, and so I had a good...

Padraic Koen posted this beautiful photo taken from the helipad at Arkaroola in South Australia. I often joke that my "office" is at the ASV's dark sky site in Heathcote, but Padraic's beats that by light years . It was at 3:59am on 6 December, and the camera, with its 11mm lens, was facing West-Northwest. Arkaroola is at the northern end of the Gammon Ranges, seriously isolated in the outback. The settlements of Copley and Leigh Creek are over 100km to the West-Southwest. These places produce pretty much zero light pollution, so the Arkaroola skies are about as dark as you'll get anywhere on the planet. There are a few things going on in this picture. First, the Moon was rising in the Northeast, out of frame to the right. This is shining gentle light onto the terrain, and the ten-second, ISO800 exposure picks out some features on the ground. This is pretty much my favourite part of the sky. At the top, Orion is dominating. Orion contains all sorts o...

Back in December 2018 I wrote about the encounter between the NASA's probe OSIRIS-REx and the asteroid Bennu . After a lengthy journey from Earth, the probe had settled into orbit and was about to begin studying the asteroid. Since then, we've learned a number of unexpected things. First, there's water there. Not a lot, but it looks like water is turning up all over the solar system. But there may have been a lot more water there in the past, with evidence that it may have actually flowed through Bennu's interior. Second, there's organic carbon there. Because carbon forms the backbone of all organic molecules such as sugars and alcohols, this might hold some clues to the origins of life. Third, and the most interesting thing (for me, at least), was that Bennu is a remnant from a larger asteroid that had been blasted to bits in a collision. This gave Bennu not only its odd diamond shape, but also its relatively fast spin. That would have been quite a sight. ...

This is the story of an asteroid, a challenge and a video. It describes why I decided to catch the dwarf planet Ceres, how I found it, how I photographed it, how I watched it make its way through the dark, and how it reminded me how little we are. Astronomy in the time of the Coronavirus The other night was the first night in weeks where it wasn't cloudy. Of course, there was a mad scramble when Melbourne-based astrophotographers were all running outside to take photos. Naturally, I was one of them. We couldn't run far though. The Melbourne Coronavirus lockdown prevented anyone from leaving their homes. The Moon was about three quarters full (waxing gibbous, if you're into that sort of thing), and not far from Jupiter and Saturn. Mars was up later. The Helix Nebula was around half way between Saturn. and Mars, and the Sculptor Galaxy followed. The asteroid formally known as... So I didn't go for the Helix or Sculptor. I decided to go for the dwarf planet Cer...

I've mentioned the dwarf planet Ceres in my posts before, but only in passing. it's a little hard to introduce Ceres, due to changing nomenclature. It used to be considered the largest asteroid, but it's now called a dwarf planet. It's certainly the largest object found in the asteroid belt between Mars and Jupiter. It's also the only defined dwarf planet this side of Neptune. We've known about Ceres since the start of the 19th Century. Astronomers had been looking for planets between Mars and Jupiter, and discovered a number. They called this group "asteroids", meaning things that are "almost, but not quite, entirely unlike stars". But the thing that's most interesting about Ceres is those white dots. Hubble got a few photos of odd bright patches on Ceres back in 2004. Aliens? Yeah, naah. The Dawn mission, when a probe orbited Ceres, found that these were patches of sodium carbonate. These had probably formed when salty water bubbled up ...

Ceres - but what is it? I've mentioned the dwarf planet Ceres in my posts before, but only in passing. it's a little hard to introduce Ceres, due to confusion over nomenclature. It used to be considered the largest asteroid, but with all the debate over asteroids and dwarf planets, I really have no idea what I'm meant to call it. It's certainly the largest object found in the so-called "asteroid belt", but also the only defined "dwarf planet" found this side of Neptune. Apart from that, well, frankly you can call it what you want in this post-modern world. Discovery We've known about Ceres since the start of the 19th Century. Astronomers had been looking for planets in the zone between Mars and Jupiter. Kepler had noticed this gap was large enough to contain a planet, but didn't seen to have one. Following a search, astronomers discovered a number of objects. They called this group "asteroids", meaning things that are ...

What's this mess? I took this disaster of a photo while looking (in vain) for a passing asteroid. A few days ago, it was a clear night in Melbourne. I took the opportunity to go out into the back yard and do some photography - as you do. What I was after was the Statue of Liberty nebula. ( I eventually posted it alongside a more concrete Statue of Liberty .) However, I'd heard about a close pass of an asteroid that was coming up, and thought I might be able to get a photo. The asteroid's name was (52768) 1998 OR2. Clearly a family name. From what I can gather, it's an egg shape, roughly 2km by 5km. That's big, and if it collided with the Earth it'd cause a heap of problems, but it wasn't coming closer than 16 times the distance of the Moon. It's also not a giant: the Chicxulub asteroid was up to 80km across. But it's large enough to be spotted with an 8-inch telescope. Mine is only a little more than half that, but I thought I'd have a stab in th...

How many moons does the Earth have? I've been watching QI for years. It's got to be one of the favourite shows for the "well, actually" crowd. One of the themes in the show is that Stephen (lately Sandi) asks a plain question, and one of the panel gives the answer that everyone thinks is right. This is a trap. One? Wrong! A while back, Stephen Fry talked about Cruithne, and claimed it was a moon of the Earth's. I wrote about this about a year back in one of my Facebook posts. So two? Wrong! The question has come up a number of times on the show, always with different answers. It's turned into a standing joke. But - for the last few months, Earth has had another companion, and it's absolutely tiny. It doesn't have a name, apart from 2020 CD3, and appears to be a captured asteroid, of between two and four metres in size. Because it hasn't been under observation for long, we really don't know when it showed up, but the orbital models indicate at l...

Yes, you CAN find a meteorite! On the 4th of January this year, an Italian dog walker found a chunk of rock that had fallen from the sky three days earlier. How did he do this? He was looking for it after having been told it had landed in the area. January 1st, 18h 26min UT fireball trajectory calculated from the 8 PRISMA/FRIPON video detections. Credit: PRISMA/FRIPON This is the first meteorite that’s been found - in Italy at least - after a targeted search. Up until now, all meteorites have been found purely by accident. Across Italy and surrounding countries, there is an extensive (and growing) network of all-sky cameras, a bit like the ASV’s camera at their dark sky site (asv.org.au/lmro_skycam). These cameras are co-ordinated by the Italian National Institute of Astrophysics, and are placed to detect meteors. Together, the system is known as PRISMA (Prima Rete Italiana per la Sorveglianza sistematica di Meteore e dell’Atmosfera). When a meteor enters the atmosphere, it get...

Researchers at Caltech have announced the discovery of an unusual (or maybe just hard-to-discover) asteroid. Known as “2019 LF6”, this one-kilometre lump is one of only 20 known Atira-class asteroids. This type of asteroid orbits entirely within Earth’s orbit.  In fact, it only just gets beyond Venus, so there’s no way it could threaten us with a collision. The only way that could ever happen is if a Bond villain strapped booster rockets to it… Even though it’s totally safe, that didn’t stop some clickbait sites from hyping it (such as “NASA astronomers spot monster asteroid near Earth that ‘eluded several decades of careful searches’”). What’s noteworthy about this asteroid is that it has a super short “year” – it goes around the sun in only 151 days. All I know about orbital dynamics is from my mis-spent years playing with Kerbal Space Program, but this suggests that the orbit is highly elliptical. The asteroid must be going at walking pace when it’s at aphelion. It also come...

27 May 2019 Yikes! Did NASA just dust New York? No, they didn’t. Don’t worry. It was all an exercise. But it makes a fun read! Recently NASA and JPL hosted a conference on planetary defence – against near-Earth objects, that is, not aliens. Part of the five-day conference was a simulation of the discovery of an object on a collision course with Earth. Each day, more information was presented, and experts were asked what the best course of action would be, including options to deflect or “disrupt” the asteroid. They also discussed what would be at risk, and how to manage and mitigate damage. The hypothetical narrative that the experts were subjected to was this: In March 2019, the asteroid is discovered, and is estimated to have an impact probability of 1 in 100. At this point, most of the effort is focused on determining the fine orbit, and the size and mass of the asteroid. By July 2019, additional information has increased the probability of impact to 1 in 10. This is whe...

5 April 2019 Last time, I talked about Cruithne, and what a weird thing it was. From the Earth, it looks as though it orbits the Earth in a horseshoe shape, going one way around, stopping, then going back the other way. It’s explainable if you look from a different perspective, because the Earth and Cruithne both orbit the Sun in the same period of time. It’s just that it looks like some bizarre orbit from the Earth. I also said that if you've got access to a large telescope you'd be able to see Cruithne - just. When I said "just", I really mean it. This is a magnitude 17-18 object, so it's incredibly dim. My low-magnification rig has imaged down to magnitude 14, when I got a photo of Uranus' moons Titania and Oberon. This was a 10 second exposure, so I'm thinking it's worth a try. Those of you with larger-aperture rigs should be able to do this. Of course, the alternative is to join the Astronomical Society of Victoria and use their equipment. A 44 in...

3 April 2019 One of the things that I’ve seen on QI a couple of times now is “how many satellites does the Earth have”? It’s a trick question. “Satellites” has a couple of different definitions. But the thing I did find interesting was when they started talking about something called 3753 Cruithne.  Pronounced Crew-EEN-ya, it’s a chunk of rock about 5 kilometres across, that orbits – well, it’s not really clear what it orbits. If you’re on Earth, it looks like it’s orbiting Earth. But from other perspectives, it looks it’s orbiting the Sun. But it gets weirder than that. If you’re on the Earth, it looks as though Cruithne goes around the Earth in a horseshoe-shaped orbit. Yes, that’s right, it seems to orbit us, approach, but then slow down and fall behind. But before the Earth catches Cruithne again, it speeds up and pulls away. I mean, what the…? It’s not that Cruithne follows the Earth around the Sun. If you looked down on the Solar System from way above the sun, you would see ...

11 March 2019 You may remember that the New Horizons spacecraft flew past a strange-shaped Kuiper Belt object in early January. This rock was eventually named “Ultima Thule”. Ultima Thule is a seriously long way away from the Earth, being about 45 times further out from the Sun - it's past Neptune. What’s it doing out there? Well, the short answer is not a lot. Its orbit is boringly round. Other Kuiper Belt objects have a tendency to cross orbits and "encounter" each other now and again. When this happens, one tends to speed up and the other tends to slow down. This affects the eccentricity (or roundness) of both orbits, which can mean one of them gets knocked out of the Kuiper Belt entirely, coming way closer to the Sun. (I don’t want to worry you, but this means “closer to the Earth” as well). Ultima Thule is not ever likely to be this exciting. Phew. But back to its strange shape. From a long time before the New Horizons flyby, NASA thought that the object wa...

4 February 2019 People in the Astronomical Society of Victoria will have heard of the Leon Mow Dark Sky Site (the LMDSS). You may have been there. But I was surprised at how little I know about Leon Mow. Leon Mow AO had a keen interest in astronomy. As part of his extensive philanthropic activities, he donated the facility to the ASV in 1990. Since then, the site has been upgraded, with a kitchen, bathroom, a club room, a dome with a telescope for use by qualified members, and most recently a number of very comfortable sleeping quarters. All these are freely available to ASV members. I use them often, and apart from walking past the plaque, I normally didn't give Mr Mow a second thought. The Leon Mow Radio Observatory is in the same location, and is fast becoming an impressive sight, with a number of aerials and (soon) a large parabolic dish antenna on a large tower. What I didn't know about Mr Mow was that his philanthropic activities extended well beyond astronomy. ...

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...