Archive for the 'Astronomy' Category

Mar 13 2023

New Asteroid Probably Won’t Hit Earth

Published by under Astronomy

NASA recently discovered a 50 meter wide asteroid whose orbit will come close to Earth. They estimate a close approach in 2046, which will likely bring the asteroid within 1.1 million miles of the Earth, about four times the distance of the moon. However, there is always uncertainty in calculating orbits, and the farther into the future you try to project their path, the more uncertainty there is. At this point in time NASA estimates a one in 560 chance that the asteroid, dubbed 2023 DW, will hit the Earth in 2046.

Orbits are calculated through multiple observations of the object along its orbit. We have to see how it is moving, and the longer the observation the greater the precision. For recently discovered objects, like this asteroid, there is more uncertainty in the orbital calculations, which is why NASA cannot completely rule out an impact. Because it is a near-Earth object, however, they will continue to make observations, refining their calculated orbit, and reducing the uncertainty.

Interestingly, the current scale for designating the risk of an object hitting the Earth, the Palermo scale, is not based on a simple percentage probability, but on the probability relative to the background rate of impacts. A Palermo scale of 0 means that the chance of a particular object hitting the Earth is no different than the background rate of impacts. The scale is also logarithmic, so a Palermo rating of 1 means a chance of impact 10 times the background rate, 2 is 100 times. 2023 DW has a Palermo rating of -2.17.

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Feb 10 2023

The Speed of Gravity

Published by under Astronomy

I recently received an e-mail question from an SGU listener about the speed of gravity. They were questioning a statement they heard by Neil DeGrasse Tyson that if the sun were magically plucked from existence, the Earth would not feel the effects for 8 minutes and 20 seconds – the time it takes for light to travel from the sun to the Earth. This blew their mind, writing: “That statement doesn’t make sense to me. What DeGrasse is saying is that we don’t actually orbit the sun but a point in space where the sun was 8 minutes 20s ago.”

Actually, that’s exactly right. He did get it. We see the sun as it was 8 minutes 20 seconds ago. We also feel the sun as it was at that time – in every way. The speed of light is more than the maximal relative velocity that energy travels through the universe, it is the speed at which reality propagates throughout the universe. No effect can exceed the speed of light – not information, matter, energy, or force.

We can use the General Relativity conception of gravity, that matter curves space time and that matter and energy travel in a straight line through curved space. You have likely seen the typical graphical representation of this, with a heavy object like a planet or star distorting a grid of spacetime like a heavy ball resting on a stretched piece of fabric. This is actually just a conceptual aid, not an accurate depiction. It is missing one dimension – space is represented as a two-dimensional fabric stretching into a third dimension. You need to add a dimension to represent reality, which is three dimensions. Some experts say that three dimensional space is being curved in a fourth dimension, but others say you can work the math to describe the curvature of 3D space without invoking a 4th spacial dimension. I’m not sure what the current consensus is – I’ll have to look deeper when I have time (if anyone has a good reference, please share it in the comments).

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Feb 09 2023

Dwarf Planet Ring Mystery

Published by under Astronomy

Scientists love mysteries, because that is where new discoveries lay. It is nice to find evidence consistent with existing theories, providing further confirmation, but it’s exciting to find evidence that cannot be explained with existing theories. Astronomers may have found such a mystery in the dwarf planet Quaoar – it has a ring where one shouldn’t be.

When we think of planetary rings we of course think first of Saturn, which has by far the largest and most impressive ring system in the solar system. But all the gas giants have their own rings, including Jupiter, Uranus, and Neptune. None of the smaller rocky planets have detectable rings. This is likely not a coincidence and relates to how rings form and how long they will last. But smaller bodies can have rings. Saturn’s moon Rhea may have a faint ring of its own. There is even an asteroid, Chariklo, which has two faint rings.

Rings are basically linear clouds of dust, ice, and other material that spreads out in an orbit around a planetary body. They form in one of two ways. For large planets like Saturn, if a moon’s orbit decays to the point where it gets within the Roche limit (the point at which tidal forces are so great they tear apart any large object), then the moon will break apart into debris that forms a ring. But anything that spreads dust around a planet can also feed a ring. For example, when meteorites hit the moons of Jupiter they throw up dust which can feed its faint ring system. Because the material that forms rings are close to their host planet they also tend to slowly rain down to the surface, so they have a limited lifetime. Saturn will eventually lose its beautiful rings. But new rings may also form. When Phobos gets too close to Mars one day it will break up and become a Martian ring system.

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Feb 02 2023

Possible Kilonova Progenitor System Identified

Published by under Astronomy

The universe is a big place, and with a variety of powerful telescopes astronomers can see it all (at least the visible universe). This means we can potentially see extremely rare events. One such rare event is a kilonova, a type of nova that results from two neutron stars or neutron star and a black hole merging together.  Even more rare – astronomers may have recently identified a system that will one day create a kilonova, in the Milky Way. They estimate that there may be only ten such systems in the entire galaxy.

To quickly review, the term “nova” means “new” in latin, because they were seen as new temporary stars that appear in the sky, last a few weeks and then disappear. A basic nova results from a white dwarf star with a close companion star. Over time the white dwarf may gravitationally pull hydrogen from the outer atmosphere of the companion star, until enough of it collects on its surface to kickstart runaway nuclear fusion, resulting in a significant brightening of the white dwarf. This is generally not explosive or destructive, and a single white dwarf can potentially go through many such novae.

There are a couple of types of supernova. The classic type of supernova results from the collapse of the core of a sun that had burned through its fuel. This rapid gravitational collapse results in an explosion of radiation, throwing off any remaining outer material and leaving behind a stellar remnant – neutron star or black hole.  The type 1a supernova results when a white dwarf draws enough material from a companion that it starts to have fusion in its core which rapidly burns through its fuel and collapses to form a supernova. A hypernova results from a very large star (30 or more solar masses) undergoing core collapse and leaving behind a black hole. (I’m skipping a lot of detail but this is basically how it breaks down.)

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Jan 20 2023

Dark Skies – A Vanishing Resource

Published by under Astronomy

When I was a child I loved looking up at the night sky and seeing thousands of stars. I especially loved seeing the disc of the Milky Way spreading across the sky. I can’t remember when this first dawned on me, but as an adult I can no longer do this. When I look up into the sky, even on a clear night, I can still see lots of stars, although not as many, and I can’t make out the Milky Way. It’s simply not visible.

The problem of light pollution was also brought home to me when I visited Australia. Seeing the southern sky was always an item on my bucket list – to see the Southern Cross, the Magellanic clouds, and Alpha Centauri. I have been in the southern hemisphere three times. The first two times I never got a look at the night sky. So on the third trip I made it a point to go somewhere where I would get a good view of the night sky. I had to drive over an hour from Christchurch to get that view. It was magical, and definitely worth the effort, but it really demonstrated for me the extent of light pollution.

A recent study published in Science found that:

Trends in the data showed that the average night sky got brighter by 9.6% per year from 2011 to 2022, which is equivalent to doubling the sky brightness every 8 years.

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Jan 12 2023

Earth-Like Planets

Published by under Astronomy

I’m still waiting. Since we developed the technology to detect exoplanets – planets orbiting other stars – I have been tracking those exoplanets that are the most Earth-like. That term, “Earth-like”, is used quite a bit in science news reporting about exoplanets, but very loosely, in my opinion. I’m still waiting for an exoplanet discovery that is fully Earth-like.

This happened again just recently with the discovery of a second planet in the TOI 700 system that is “Earth-sized” (that’s more accurate than saying “Earth-like”). Unfortunately, TOI 700 is a red dwarf, which means the two Earth-sized planets technically in their habitable zone are also likely tidally locked. Further, red dwarfs are unstable compared to orange or yellow stars and may strip the atmospheres from any planets close enough to be in the habitable zone.

Before I review the best candidates – what makes an exoplanet “Earth-like”. The two criteria that seemed to be used by most reporting is that they are small rocky planets in their generously defined habitable zone. Often the term is applied to so-called “super-Earths” which are more massive than Earth but less massive than ice giants – basically anywhere between Earth and Neptune. It seems astronomers agree on an upper limit of mass of 10 Earth masses, but disagree on the lower limit (anywhere from >1 to 5). They should just pick a number. I think something like 2 Earth masses is reasonable, but perhaps it’s better to use surface gravity. We can use the formula a=GM/R^2 to determine surface gravity. So, for example (if I did the math right) a planet with 2 times Earth’s mass and 1.2 times the radius would have a surface gravity of 1.38 G. What about the lower limit? I would suggest somewhat larger than Mars – we could make an arbitrary cutoff of 0.5 G surface gravity.

The habitable zone is the distance from the parent star where it is possible to have liquid water on the surface. But there are lots of other variables here as well, mainly relating to the atmosphere. Venus, for example, is technically in our sun’s habitable zone, as is Mars, but neither are habitable. If Mars had more atmosphere and Venus less, however, they could have a survivable environment.

I think exoplanets around red dwarfs at this point need to not count as “Earth-like” even if size and temperature are in the range. They would have to be very close to their parent star, which means they are likely tidally locked (in itself not a deal-killer) and likely don’t have much of an atmosphere. There may be exceptions to this, and there are lots of red dwarfs so we may ultimately find some special planets around red dwarfs with life, but for now it is so unlikely they should simply not be on the list. Orange and yellow suns are the best candidates. Larger and brighter than yellow and the lifespan of the star becomes too short, but still may be a candidate with the right conditions for people to settle. Moons of gas giants are another possibility, but the variables get more complicated.

So to be truly Earth-like we would want a planet with a surface gravity somewhere between 0.5 and 1.3 that of Earth, that is small and rocky, and that orbits an orange to yellow star in the habitable zone. But there are other things that can go wrong with any candidate world. We also need to consider what question, exactly, we are asking. Are we interested in worlds we could one day settle? That would mean they also need to be very close, within 20 light years or so. Are we looking for a world that is already harboring life, and how much time would we want for that life to have had to evolve? This is important if we are looking for technological civilizations.

Here is a list of the ten most Earth-like exoplanets discovered so far. None really meet my criteria. Most orbit red dwarfs.  Some are super-Earths.

It’s too early to be discouraged, however. Some of our planet-finding techniques favor larger planets, or ones very close to their host stars. It is therefore harder and takes longer to discover small rocky worlds at Earth like distance from their stars. Astronomers estimate there are 300 million to 40 billion Earth-like planets in the Milky way. That is still a huge variance, but taking an average figure, that’s a lot. That number will be refined as we search more stellar systems for their planets. There are about 100 billion stars in the Milky way, but many of them are in multi-star systems. Astronomers estimate that 1 in 5 systems have at least one “Earth-like” planet, but again, I wonder what definition they are using. Most of these are likely red dwarfs (because most stars are red dwarfs).

Hopefully they will nail down these numbers with higher confidence in the near future. It would also be nice to complete a survey of all the closest stars to our system. Meanwhile I will keep tracking new discoveries.


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Dec 06 2022

Mars More Volcanically Active Than We Thought

Published by under Astronomy

Mars is perhaps the best candidate world in our solar system for a settlement off Earth. Venus is too inhospitable. The Moon is a lot closer, but the extremely low gravity (.166 g) is a problem for long-term habitation. Mars gravity is 0.38 g, still low by Earth standards but better than the Moon. But there are some other differences between Earth and Mars. Mars has only a very thin atmosphere, less than 1% that of Earth’s. That’s just enough to cause annoying sand storms, but not enough to avoid the need for pressure suits. Mars lost its atmosphere because it was stripped away by the solar wind – because Mars also does not have a global magnetic field to protect itself. The thin atmosphere and lack of magnetic field also exposes the surface to lots of radiation.

Mars’ smaller size also means that it cooled faster than the Earth. While there are ancient volcanoes on Mars, the surface crust looks solid, without plate tectonics. This has led astronomers to believe that Mars is a quiet planet, with heat at the core, but a solid crust and mantle and no geological activity. That also means there are no recent volcanic eruptions that might replenish its depleted atmosphere. However – that view is changing.

There is one region of Mars, Elysium Planitia, which may be geologically active. In fact, there is now good evidence of a giant mantle plume under the surface. A mantle plume occurs when hot magma from the core rises up through the mantle and pushes up against the overlying crust. There are more than 18 such mantle plumes on Earth. One is right below the Hawaiian islands – as the Pacific plate moves over this plume it creates a chain of volcanoes and resulting volcanic islands. What is the evidence for a mantle plume beneath Elysium Planitia?

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Dec 05 2022

Square Kilometer Array

Published by under Astronomy

Construction begins this week on what will be the largest radio telescope in the world – the Square Kilometer Array (SKA). This project began more than 30 years ago, in 1991, as an idea, with an international working group forming in 1993. It took three decades to flesh out the concept, create a detailed design, secure the land rights, and secure government funding. The first antennas will go online by 2024 with more added through 2028 (which will complete the first phase – about 10% of the total planned project). This will result in a radio telescope array with a total area of one square kilometer.

There are actually two components to the total array. One is being built in Australia, the SKA-Low, for low frequency. These will use antennas that look like two-meter tall metal Christmas trees. There will be 500 arrays of 256 antennas for a total of 131,000 antennas. This will be the low frequency array, able to detect radio waves between 50 megahertz and 350 megahertz. There will also be SKA-Mid in South Africa, which will be an array of 197 dishes sensitive between 350 megahertz and 15.4 gigahertz. The whole thing will be connected together, with the bulk of the computing power located in the UK.

Why do astronomers connect radio receivers together? This has to do with interferometry – the ability to combine two signals so that they can simulate a single receiver with a diameter equal to the distance between the two receivers.  It’s not the same as having one giant dish, however. An array increases the resolution of the received image, but the sensitivity is still a function of the total receiving area (not the distance). The Very Large Array (VLA) in New Mexico has radio dishes on rails, so that they can be moved into different configuration. By moving the dishes apart you can achieve greater resolution, but by moving them closer together you get greater precision – so there is a trade-off from moving receivers farther apart. There is no substitute for total collecting area, which is why the SKA will have so many individual receivers.

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Oct 21 2022

More Precise Measure of Hubble Constant Solidifies Mystery

Published by under Astronomy

Cosmologists have recently published the updated results of an extensive analysis of the overall structure of the cosmos, with interesting results. It both solidifies our current understanding of the universe, but also reinforces a conflict that scientists have not been able to solve.

The story begins with Type IA supernova. A supernova is when a star explodes because of runaway fusion in its core. Different stars of different masses and compositions will explode with different energies and therefore intrinsic brightness. But a Type IA is caused by a white dwarf star in a binary system which is leaching matter off its companion. The white dwarf slowly gains mass until it reaching the Chandrasehkar limit, the point at which its gravity overcomes the outward pressure of heat and energy, the star then collapses and goes supernova. This means that all Type IA supernova are the exact same mass when they explode, which further means that they should have the same intrinsic brightness. In reality there is some variability in peak brightness based on other variables like composition, but astronomers have learned to make adjustments so as to arrive at a precise measure of intrinsic brightness.

Knowing the intrinsic brightness of an astronomical object is hugely useful. It means we can calculate based on its apparent brightness exactly how far away it is. Such objects are known as standard candles, and the Type IA supernova are perhaps the most useful we have. Type IAs are also really bright, outshining entire galaxies, which further means we can see them really far away, about 10 billion light years. There is also a lot of them happening around the universe. Looking far away is also looking back in time, so Type IAs not only allow us to measure the cosmos, but also to measure it throughout its history (back to 10 billion years).

It was observations of Type IA supernova that allowed astronomers to first determine that the universe is not only expanding, it’s accelerating. Since then astronomers have been gathering data on Type IAs in a project called Pantheon. The catalogued more than 1,000 Type IAs providing the most precise measure of the rate of the universe’s expansion, called the Hubble Constant. Now they have published what they are calling Pantheon+, with an expanded database of over 1,500 Type IA supernova. They have also been able to tweak their methods to make more precise measurements, account for more factors, and essentially give a much more detailed account of the Hubble Constant at different times throughout the history of the universe.

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Oct 17 2022

Electric Universe Is Crank Pseudoscience

Science is fun, interesting, and empowering, but it is also hard, especially at advanced levels. Even at a basic level, science forces you to think clearly, precisely, logically, and objectively. It therefore challenges our preconceptions, our biases, our hopes and desires and replaces these things with indifferent reality. Science becomes progressively tricky the more advanced it becomes, requiring an increasing fund of knowledge and mastery over subtle concepts and technical skills in order to be able to take the next step. At the cutting edge of science, nothing short of years of dedicated study is necessary to engage meaningfully with the enterprise of advancing human scientific knowledge. You also have to be able to engage productively with a community of scientists, all picking apart each other’s work.

It’s for these reasons that there is a lot of bad science out there. There are also those who prioritize things other than the pursuit of scientific knowledge, such as money, fame, or advancing an ideology. Many people mean well, but simply get the science wrong. Even successful scientists can make egregious errors, stubbornly stick to false ideas, or let their own ideology get in the way. So what is the average science enthusiast to do? Unless you have a fairly high level of scientific expertise in general and also in a specific field, you cannot hope to engage with the cutting edge of that field. To some extent, you have to trust the experts, but what if the experts disagree, or some of them are just wrong?

There is no easy answer to this, but there are skills and methods other than actual expertise in a specific field that can help a layperson have a pretty good idea which experts to listen to. This requires some scientific literacy, especially about how proper science operates. It also requires a certain amount of critical thinking skills – knowing something about logic, self-deception, and the nature of evidence. Further, we can learn to recognize the different types of pseudoscience and pseudoscientific behaviors, which can act as reliable red-flags to help spot fake science. Recently promoters of the Electric Universe have appeared in the comments to this blog, and this is a good opportunity to review these red flags.

The idea of the electric universe (EU) is that electromagnetism actually does most of the large-scale heavy lifting when it comes to the structure of the cosmos, displacing gravity as the main long-distance force. There are different flavors of EU, with some doing away with gravity completely, and others allowing for some gravity (to help explain phenomena EU can’t) but still relegate it to a minor role. One major example is that EU proponents believe stars are fueled by electromagnetism, and not by gravity-induced fusion. Here are two great videos that give a concise summary of the history of EU belief and why it is complete and utter nonsense. But I will review the major problems with EU and use them as examples of crank pseudoscience.

Crank pseudoscience is a flavor of pseudoscience that operates at a technically sophisticated level, but is missing some of the key elements of actual science that doom proponents to absurdity. But it also contains many of the generic features of pseudoscience. Let’s review, starting with features more typical of crank pseudoscience.

Does not engage meaningfully with the scientific community.

Science is a collaborative effort, especially at the advanced cutting edge level. This is because it is so difficult at this level, you need the self-corrective process of peer-review, rejection of error, criticism of wrong ideas, challenges for evidence and by alternative theories, etc. Without this self-corrective process, fringe groups or individuals tend to drift off from reality into a fantasy land of their own creation, although gilded with the superficial trappings of science. EU proponent Montgomery Childs exemplifies this in an interview (in the second video above) when he tries lamely to justify not bothering to publish any of his findings in scientific journals. Actual experts in plasma physics and cosmology therefore just ignore his fringe work – unless they have data to look at, they don’t have much of a choice. This is a core feature of crank pseudoscience – cranks tend to toil alone or in small fringe echochambers and not engage with proper experts.


Work outside their actual area of expertise (if they have one).

Often we see scientists or engineering getting into crank science when they venture beyond their specific area of expertise. Sometimes this is just hubris – in fact we joke about the Nobel Prize effect, where some Nobel Prize winners go on to support pseudoscience later in their career. There is also an aging-scientist effect where researchers toward the end of their career start looking at their legacy, or lack of one, and want to make a big splash somewhere. Some choose a small fringe pond where their credentials make them a big fish, and start promoting nonsense. The problem, of course, if that being an expert in one area does not equip you to contradict actual experts in a separate field. Electrical engineers are not cosmologists or physicists. It is therefore helpful to see what the most appropriate experts say about a theory, not just anyone with letters after their name. Actual experts reject the EU as completely nonsense (with good reason), and its proponents are all in unrelated fields.


Make grandiose claims while minimizing actual scientific knowledge.

The EU claims to overhaul much of science, which is itself a red flag. It is hard to prove that established science is all wrong, and it’s getting harder as science advances and the foundational concepts of science are increasingly supported by evidence and derivative theories. What cranks often do is grossly exaggerate what is currently unknown in a scientific field, or the meaning of anomalies, and they downplay what is known with confidence. This often become simply lying, making boldly false claims about the state of the science. EU proponents, for example, ignore or deny the evidence for the Big Bang, black holes, stellar fusion, and gravity. The claim that they have overturned pretty much all of astrophysics, stellar astronomy, General Relativity, and more – all on the flimsiest of pretexts. In other words, they reject theories supported by a mountain of evidence, and replace them with theories that have (at best) an ant hill.


They don’t actually explain 0r predict anything.

Another core feature of science is that it makes testable predictions. What this means is that there has to be some way to determine if one theory is more correct than another, because they make different predictions about what we will observe in the universe or the result of experiments. Scientific theories also should have explanatory power (it can explain what we see) – but this is actually necessary but insufficient feature of science. Astrology has explanatory power – if you are willing to just make up BS explanations for stuff. It’s easy, and pattern-seeking humans are good at, finding explanations of stuff. The problem with EU is that it really does neither – predict or explain. In fact, shifting from current cosmological theories to EU would be a massive step backwards. EU cannot explain a ton of established phenomena that are well explained by current theories, such as the evidence for black holes or dark matter, the lifecycle of stars, the existence of neutrinos from stellar fusion, and many more. There are also fundamental problems with EU, such as the known behavior of electromagnetism and charged particles. What EU proponents do, rather, is simply hunt for patterns, and then make very superficial connections between some aspect of EU theory and some astronomical phenomenon.

This is what triggered some of the comments – the regular rings of dust found around WR140, caused by the periodicity of the wind-binary star system. EU proponents said – look, concentric rings. We see those in the plasma dohickey thing. They then count that as a “prediction” when it was actually just retrofitting, and not very well. They falsely call the rings “perfect” when it is the very imperfections in the rings that can be accounted for by the astronomical explanation.


Portray the scientific community as a conspiracy of the small-minded.

If you have a nonsensical fringe theory and don’t publish your findings (except in fringe journals created for that purpose), it’s likely that the broader scientific community with ignore or reject your claims. They should – you have not earned their assent by demonstrating your claims with objective and publicly available evidence. When that happens, cranks universally claim they are the victim of a conspiracy. They don’t self-correct, address legitimate criticisms, recognize the shortcomings of their theories, do better experiments or, in short, engage in legitimate science. They cry foul. They say something to the effect that “mainstream” science is all a conspiracy, and scientist are simply too dumb or too scared to recognize their towering genius. This is the point that self-comparisons to Galileo or Einstein are typically brought out.

EU proponents do this in spades. There is a large, vibrant, world-wide community of astrophysicists, all at different parts of their career, in different countries and institutions, just trying to figure out how the universe works and hopefully make a name for themselves doing so. Yet a few fringe scientists, without the proper expertise, allege they have proven all of them hopelessly wrong, because they are all biased or don’t know what they are doing. And they are stubbornly not convinced by silly superficial evidence its proponents won’t bother to publish. Imagine!

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