Cassiopeia’s Illusion

Cassiopeia, the elegant constellation which hovers year-round in the skies of the Northern Hemisphere is typically recognized by its more simple asterism shaped like a “W” with a slight tilt on one side. (An asterism is a prominent pattern or group of stars, typically having a popular name but smaller than a constellation.)

(Image of Cassiopeia is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.)
Stars of Cassiopeia

The constellation represents the queen of Aethiopia*, the mother of Andromeda in Greek mythology. It’s interesting to note that the Andromeda constellation lies adjacent to Cassiopeia in the night sky. Cassiopeia as a constellation has been known for a long time, as it was listed as one of the 48 original constellations in the 2nd century by Greek astronomer, Ptolemy. Today that list has been extended to 88 official constellations by the International Astronomical Union (IAU).

(*Aethiopia were ancient lands in the area of the upper Nile, not to be confused with modern day Ethiopia.)

The asterism is made up of five stars that can be seen in the illustration below, which shows their distance from Earth and their apparent and absolute magnitudes.

Cassiopeia in 3-D (Click on the picture to see a larger image.)

The table below lists the stars that make up the asterism, arranged in order of their distance from Earth:

What makes Cassiopeia’s asterism remarkable is that four of the five stars appear to be very close in brightness with their apparent magnitudes varying about 1.5 times from the dimmest, Ruchbah (2.68), to the brightest, Navi (2.15). The fifth star, Segin, is notably dimmer than the rest (3.35) but still is fairly bright. (Remember, the more positive the number, the dimmer the star.) This uniformity in brightness gives the impression that the stars are all the same size and distance from Earth.

Being about the same brightness is, in itself, not all that noteworthy until you look at their absolute magnitudes, their distances from Earth and how they work together to create the constellation we see and give us Cassiopeia’s illusion.

To understand what’s happening one has to remember that light has a property that its intensity diminishes by one over the distance squared (1/d2). A candle two feet from you is ¼ the brightness it is one foot away. So one naturally expects to see the stars get dimmer the further away they are. But, that’s not what we see with Cassiopeia.

Starting with the closest star, Caph, 54 light-years from Earth, and moving further out we see that each successive star’s absolute magnitude is more negative (i.e. brighter) than the preceding one:

  • Ruchbah is twice as far as Caph, and it’s 3.7 times as bright – almost 4 times. “If” Caph and Ruchbah had the same absolute magnitude, and Ruchbah was at twice the distance of Caph, we would expect its apparent magnitude to be ¼ that of Caph’s, but that’s not what we see. Ruchbah is almost 4 times brighter. Its intrinsic brightness is such that it compensates for being twice as far away. So it appears to us to be about as bright as Caph.
  • Likewise, Schedar is 4.2 times further and 18 times brighter. If we take the square of the distance – (4.2 x 4.2 = 17.6) – almost 18. Schedar’s intrinsic brightness compensates for the distance, again making it appear to be as bright as Caph to us.
  • Navi is 10 times further but 115 times brighter – that’s pretty close to 10 x 10 = 100 – the square of the distance. Again Navi’s brightness compensates for the greater distance.
  • Segin doesn’t follow this pattern and is dimmer than the rest. If it had an absolute magnitude of -3.1 instead of -2.16, it would be about 50 times brighter than Caph and at its distance from Earth it would have about the same apparent magnitude.

So, through random chance of the stars’ distance and intrinsic brightness, the stars of Cassiopeia very closely compensate for the 1/d2 reduction in the intensity of light over distance. So we see them to be all about the same brightness from here on Earth.

(Note that intervening dust and gas along our line of sight can cause the star to appear dimmer and therefore perceived to be further away than it really is. This is one of the many sources of error that astronomers have to take into account when measuring the brightness and distance of stars.)

So how do these stars make up for their distance?

The other stars in the asterism are hotter and bigger than Caph, especially the more distant stars. Caph is a yellow subgiant, about as hot as our Sun but 28 times more luminous. Navi and Segin are very hot blue stars with luminosities of 161 and 57 times Caph’s luminosity, respectively. Schedar, although a cooler orange-red giant star, is 32 times more luminous than Caph. Even Ruchbah, a more typical main sequence star, is 2.3 times more luminous than Caph.

So, how bright a star appears to be in the night sky is determined not only by its distance and the dust and gas that might lay between it and the observer, but it also its intrinsic brightness. This is a property of the star which depends on how big and how hot it is. So Mother Nature’s distribution of stars in the cosmos can conspire to present us with the illusion, at least for Cassiopeia, that all these stars are the same size and distance from us.

Till next time,

RC Davison


Navi information:

Stellar Systems in Orion

As we head into summer, Orion has departed the northern nighttime skies and will reappear in the chill evenings of autumn. Looking at this distinctive constellation, we are dazzled by the bright stars that define its form: Betelgeuse, the red supergiant of Orion’s left shoulder; Rigel, the blue supergiant that marks his right leg; Saiph, the blue giant for his left leg; Bellatrix, another blue giant that marks his right shoulder and the blue giant and supergiant belt stars, Alnitak, Alnilam and Mintaka.

Orion“, plate 29 in Urania’s Mirror, a set of celestial cards accompanied by
A familiar treatise on astronomy …by Jehoshaphat Aspin. London. (Sidney Hall, Public domain, via Wikimedia Commons)

As impressive as these stars are, there is more to three of them than meets the human eye. What we see as single stars with the naked eye are in reality multiple star systems containing from three to as many as six stars doing a celestial dance together that is governed by the laws of physics.

In the illustration below we can see that Rigel, Mintaka and Alnitak, plus an additional star system, Sigma Orionis, which lies in a cluster of stars just below the left-most belt-star, Alnitak, are multiple star systems. The Orion Nebula itself is a literal star factory containing over 3000 stars with more than 700 of them in various stages of development. There are over 150 stars in this region that have protoplanetary disks – dusty regions around the stars where planets may be forming.

Stellar systems of Orion. Click on image for larger view.

Note that in the illustration the stellar orbits are not to scale, and the orientation of the orbits do not reflect the actual orientation relative to Earth, but the size of the stars displayed are to scale with the Sun’s size shown for reference. One can easily see that the Sun is dwarfed by even the smallest of these stars, which in turn are minuscule relative to the supergiant, Rigel, which is 79 times the size of our star and has 21 times the mass.

The Alnitak and Rigel systems contain pairs of stars that orbit too close together to be resolved (seen as separate stars) using the current state-of-the-art optical telescopes we have available today. These binary systems were discovered by looking at the spectrum of the stars’ light and how it shifts over time. Check out this great article on how spectral binary stars are identified.

Rigel has the most complex system in Orion with four stars. The spectra pair, Ba/Bb, orbit each other every 9.9 days and they orbit about a common center with Rigel C every 63 years. This trinary system obits about Rigel with a period of 24,000 years.

The Mintaka system has five stars in two systems: a binary consisting of Mintaka C/B, which may or may not be gravitationally part of the trinary system made up of the pair, Aa1/Aa2, with a period of 5.7 days, and Mintaka Ab, which orbits around the pair with a period of 350 years.

Alnitak’s spectra binary system, Aa/Ab, has a longer period of 7.3 years. Aa, a supergiant, is 20 times the size of our sun and has 33 times the mass. The smaller partner, Ab is 7 times the size of the sun. This pair is in orbit with a third star, B, and has an orbital period of just over 1500 years. Some references mention the possibility of another star in the group, but as of yet it has not been proven to be gravitationally bound to the system.

A less prominent star, Sigma Orionis, found within the Orion constellation contains a close binary pair Aa/Ab, which is made up of stars very similar in size and mass. (About 5 times the size of the sun.) They orbit each other every 143 days and the pair orbits another star, also similarly sized, with an orbital period of 160 years. These stars cast light on the famous Horsehead nebula of Orion.

σ Orionis (lower right) and the Horsehead nebula. The brighter stars are Alnitak and Alnilam. (Credit: ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin)

The Orion Nebula is a vast stellar nursery filled with gas and dust which constantly feeds the growing stars. Some of these stars or protostars are cultivating disks of dust and gas that will eventually coalesce into planets. The two images below show Orion in visible light on the left and in infrared light on the right. The longer wavelengths of the infrared light pass through the dusty veil of the nebula giving us a clearer picture of what’s going on inside. Over the millennia to come, there may be many more stellar systems evolving and becoming visible as the nebular dissipates.

Orion Nebula in optical light (Wikimedia Commons:
Orion Nebula in Infrared light. (ESO/H. Drass et al.)

The cosmos contains so many wonders and we, with our limited senses, have barely scratched the surface to see and understand what is out there!

Till next time,

RC Davison







Chandra article on Mintaka:

Sigma Orionis:

Orion Nebula

Orion In 3D Revisited

With the red giant, Betelgeuse, popping up in the media, I thought it would be a good time to take another look at Orion and the stars that make up this iconic constellation.  Consider this an update to my earlier post “The Multidimensional Constellation, Orion” way back in 2014 – when Orion was behaving himself. (Check the post for more detail on the constellation and its stars.)  In the fall of 2019 Betelgeuse began to dim dramatically, leading many to wonder if it was the time for Betelgeuse to exit stage right in a blazing supernova.

Orion Constellation and Nebulae. Rogelio Bernal Andreo / CC BY-SA (

So Betelgeuse didn’t fade away to oblivion nor did it flash into a supernova, but after losing two-thirds of its brightness it began to recover its luster in February of 2020. Studies just released indicate that the supergiant may have ejected a large mass of hot gas in our general direction that coalesced into dust grains as it cooled and began to block the light from the star. Is this a precursor to the star going supernova? We don’t know. The star will eventually meet that fate, but it could be tomorrow or in the next 100,000 years. Stay tuned!

While reviewing the seven major stars that make up Orion I came across a revised estimate for the stars’ distances from Earth and updated the illustration of Orion in 3-D to reflect this new data. The new data adjusts the distance to most of the stars, mostly closer, but Alnilam, the central star in Orion’s belt, shifted from 1359 light years (ly) to 1976 ly.









Original Distance (ly)








Revised Distance (ly)








Orion’s stars in 3D with new distances based on new Hipparcos reduction. (Click on image for larger version.)

The fact that Alnilam may be 617 ly further away and that its brightness did not change, means that this star is a lot bigger and a lot brighter than previously thought. Alnilam went from being about 375,000 times as bright as our Sun to 832,000 times brighter at this new distance! Also, because of this extra distance the star’s diameter must be larger, changing from 24 times the radius of the Sun to 42 times.

It’s difficult for us to grasp these numbers but there is a way to compare the brightness of these stars and that is to use their ‘absolute magnitude’ as opposed to their apparent magnitude. The apparent magnitude of a star is the brightness of the star as we see it normally in the night sky. Absolute magnitude is the magnitude, or brightness if you will, of the star if it were at a fixed distance from the Earth. The distance that is used is 10 parsecs, where a parsec is 3.26 ly, so the star would be placed at 32.6 ly from Earth and its magnitude recalculated at this new distance.

The apparent magnitude of our Sun is -26.7 (Note, the more negative the number for magnitude, the brighter the object.) if it were moved to 10 parsecs its absolute magnitude would be, +4.83. At +4.83 the Sun would be difficult to see at night with the naked eye, especially with the light pollution we have in cities and towns.  Note that Venus is typically between -2 and -4 when it is visible in the evening, substantially brighter than our Sun would be at 10 parsecs.

Below is table that shows the apparent and absolute magnitude for the stars of Orion.









Apparent Mag








Absolute Mag








One can see that Alnilam is the brightest star in the constellation, surpassing Rigel. So how bright is this?

If Orion’s stars were all at 10 parsecs from Earth, most of the stars would be visible during the day! The illustration below shows an approximation of what one might see. The average magnitude of the brightness of the midday sky is about -4, so all of these stars, except Bellatrix, would be brighter than the sky. Saiph and Mintaka would just barely be visible in the sky, but Rigel and especially Alnilam would stand out prominently. At 10 parsecs, Orion would be amazingly bright constellation at night; out-shining everything but the full moon!

The constellation of Orion would be visible during the day if all of its stars were moved to a distance of 10 parsecs. (Click on image for larger version.)

There is one thing to keep in mind with these numbers, and that is that they are estimates with inherent errors due to the difficulties in determining the exact distance of the stars from Earth.  That uncertainty affects all other calculated values, so you may see the distance, diameter, mass and magnitude values for these stars and others vary from source to source depending on how the data was used.  It doesn’t mean they are wrong; just that we don’t have the technology to absolutely determine their distance.  With each new terrestrial telescope we built, and each new telescope we put into space we refine our measurements and advance our knowledge of the celestial objects that make up the cosmos.

Orion will be rising in the evening in the Northern Hemisphere towards the end of October, so it will be a good time to take a look at this wonderful constellation in person, and keep an eye on Betelgeuse. If you are inclined to do a bit more that just observe with the naked eye and would like to photograph Orion in all its splendor, check out this informative guide to astrophotography.

Till next time,

RC Davison


The HGY Database:

Validation of the New Hipparcos Reduction:

Alnilam, The Brightest Gem in Orion’s Belt:

Bridge to a Galaxy Far

Two new images are available in the gallery:

Bridge to a Galaxy Far:

Globular clusters orbit around the center of a galaxy, (Our Milky Way Galaxy has about 150 of them.) and in this image the inhabitants of a planet in one cluster have the pleasure of seeing their parent galaxy rise in all it’s glory every night. As they watch the galaxy rise, there’s more than one set of eyes in the galaxy admiring the globular cluster rising in their night sky.

Bridge to a Galaxy Far


A follow-up to “Bridge to a Galaxy Far”: Morning comes with the rising of the parent gas giant and sister moon as the nearby galaxy that dominated the night sky sets.

Bridge to a Galaxy Far – Morning


Till next time,

RC Davison


Globular Clusters – Abode for Life?

The cosmos holds many wondrous things to capture our attention, but to me, the site of a globular cluster is just mesmerizing. These bejeweled orbs can contain tens of thousands to millions of stars in a sphere that can be about 100 light-years (ly) across. (Compare this with our Milky Way spiral galaxy that is approximately 100,000 ly across and contains on the order of 300 billion stars.) There are close to 150 globular clusters orbiting our galaxy, which is not unique; other galaxies have thousands or more in orbit about them.

The globular cluster Omega Centauri, visible from the Southern Hemisphere

Image credit: Joaquin Polleri & Ezequiel Etcheverry (Observatorio Panameño en San Pedro de Atacama)

Globular clusters are made up of very old stars, on the order of 10-13 billion years old. Note that the current estimate for the age of the Universe is about 13.8 billion years old, so these stars are ancient, especially when you compare them to our Sun, which is around 4.5 billion years old. The stars that comprise a cluster are typically smaller, cooler dwarf stars designated as M-class that burn their fuel very slowly giving them their longer lifetime. The larger, hotter stars burned themselves out long ago in brilliant supernovae, peppering the cluster with heavier elements necessary for rocky planet formation. Because these stars are so old, planets that may form in their habitable zones have a greater chance of developing life. But, being in a globular cluster brings its own hazards, which would be a detriment to the evolution of advanced life.  Check out the article by astronomers William Harris and Jeremy Webb, “Life Inside a Globular Cluster“, which discusses some of the potential hazards of living in a globular cluster. (The link will download a pdf of the article.)

The very nature of the cluster, with its large number of stars so close together presents the opportunity for neighboring stars to disrupt the formation of planets or even steal planets from each other. Planets may also be ejected from a stable system by the gravitational influence of a passing star and follow their own path through the cluster. This is not to say that there would not be planets in stable orbits around stars in the cluster, although to date, no planets have been located in a globular cluster. The cluster itself makes it very difficult for us to detect planets orbiting its stars. Take a look at a previous post “Stars in Motion” which has a video showing the somewhat chaotic motion of stars in a globular cluster. It’s not the well ordered system one might intuitively expect from a gigantic ball of stars.

To get a perspective on how dense a cluster is, consider that our nearest star, Proxima Centauri, which is 4.2 ly from us. If you were to map out a sphere at the center of a globular cluster with a radius of 4.2 ly it would contain on the order of 10,000 stars instead of two! These stars would be less than a light-year apart.

A paper was recently published, “Globular Clusters as Cradles of Live and Advanced Civilizations” by Dr. R. DiStefano et al, which discusses the possibilities of planets forming around stars in a globular cluster and surviving long enough for life to form and flourish. But, this is conditional on the planets forming around stars that are located in a “sweet spot” in the cluster; that is, far enough apart that they don’t interfere with each other. Planets that form in the habitable zones of these cooler stars would be less prone to having their orbits disrupted by a passing star because these zones are close to these less massive, cooler stars.

Ringed gas giant with habitable moon on the periphery of a globular cluster. (Click for a larger image.)

A benefit of the stars being in such close proximity is that it makes the possibility of traveling to or communicating with another civilization so much more practical and if advanced life formed, probable.  Also, the high concentration of stars means that planets that have been ejected and not captured by another star may still receive enough light continue to nurture life, especially if the planets retain or generate enough heat to keep water liquid, even if under a layer of ice.

All of this makes me wonder what it would be like to view the cosmos from inside a cluster or just outside of a cluster. The image below represents a possible view of a planet inside the cluster, some distance from the center. The ambient light from all the stars would make nighttime about as bright as dusk/dawn on our planet. Consequently, the beings populating this planet might have a great understanding of the stars around them, but their view of the universe outside of the cluster would be greatly hampered by this collection of stars.

View from inside a globular cluster. (Click for a larger image.)

Check out the very interesting short story by Issac Asimov, “Nightfall”, which is about a civilization that evolved in a globular cluster on a planet with the six suns. They experience constant daylight except once every two thousand and forty-nine years when five of the stars align on one side of the planet and the sixth is eclipsed by a moon unveiling nighttime and all the wonders of the night sky, which they are very unprepared for.

Whether globular clusters are abodes for life or not will not be answered soon. It’s just one more challenge for astronomers to unravel as they sharpen their skills in exploring our amazing cosmos.

Till next time,

RC Davison

A Comet, a Moon and a Planet – a Tale of Two Tails


Comet Catalina by Greg Hogan

Sometimes a picture captures just the right moment in space and time and shows us more than the obvious when we take a closer look. The great picture above, taken by Greg Hogan shows the comet Catalina visiting the morning sky with the crescent Moon and blazingly bright planet Venus. Focusing in on the wispy comet just left of center at the bottom of the image, one will notice that it looks more like a clock captured at five minutes before four. This image shows very nicely the two distinct tails that a comet can form as it dives into the inner solar system to swing around the Sun and back out again. The two tails accompanying a comet are distinctly different: one being a dust tail and the other an ion tail.

The coma or cloud around the head or nucleus of a comet, along with its tails start to form out around the orbit of Mars as the comet warms with the increasing amount of energy it’s receiving from the Sun. The comet is composed of ice (frozen gases, and water), dust, dirt and rock and is sometimes referred to as a “dirty snowball”. As it moves closer to the Sun it continues to heat up, and the ices begin to sublime or convert directly to a gas without going through a liquid phase. This release of gas carries dust particles with it, which destabilizes the comet’s surface allowing larger particles to be released, all of which contributes to the coma and tails. Intense jets of gas, can push even more material away from the comet. It is this debris trail that becomes the source for an annual meteor shower if and when the Earth crosses the path of the comet, such as the Perseids we see in the middle of August every year, which is from Comet Swift-Tuttle.

The dust tail reflects the sunlight and appears white in color similar to the coma. The dust is launched from the comet’s surface and slowly moves away from its host. These particles will begin orbiting the Sun on their own trajectory as they escape the gravitational influence of the comet. They are also pushed away from the comet by the radiation pressure from the Sun. This radiation pressure is due to the transfer of momentum from a light particle (photon) to the dust particle when they collide. This is exactly how a solar sail works. The dust tail will flow behind the comet and as the comet rounds the Sun the tail can become curved as the particles of dust are pushed by the light, as can be seen in the image below of comet McNaught.


Comet McNaught’s dust tail – Image by Robert H. McNaught

The gas particles that are released by the comet will form the ion tail It is typically bluish/greenish in color and occurs because these gas particles liberated from the comet become “ionized” or charged by the high energy ultraviolet light emitted by the Sun. Once the atoms and molecules of gas become charged they will now be influenced by the magnetic field associated with the solar wind that comes from the Sun. The solar wind is a collection of high energy particles that the Sun radiates and entrained with this stream of particles is a magnetic field pointing away from the Sun. So the ion tail will point directly away from the Sun while the dust tail indicates the path the comet has taken. The ion tail can exhibit knots and twists due to the magnetic field as can be seen below.


Comet Catalina’s twisted ion tail. Image courtesy of CometwatchUK

The  amazing image below shows comet Encke being buffeted by a coronal mass ejection (CME) from the Sun. The comet’s tail detaches as the mass of solar particles sweeps by and then quickly reforms. This is believed to be caused by the magnetic field retained in the CME interacting with the ion tail’s field. The video is from NASA’s STEREO solar mission.

Comet Encke’s interaction with a CME

If you look in Greg’s picture at the Moon you will see that it is illuminated on lower right hand side by the Sun, which is out of frame in the lower right. Now look closely at comet Catalina and at the “minute hand” of the clock – the ion tail; it’s pointing directly away from the Sun, while the “hour hand” – the dust tail is pointing more towards the Sun indicating that the comet is moving away from the Sun and heading back out of the solar system.  Catalina passed closest to the Sun on November 15, 2015 and will be closest to Earth on January 12, 2016.

Comet Catalina will make only a one-time appearance, as it has gained enough energy on its dive through the inner solar system that it will be jettisoned into interstellar space, never to return. On its journey it will pass through two large reservoirs of comets and other leftover debris from the early solar system that orbit our star, the Kuiper Belt and the Oort Cloud.

Comets originating in the Kuiper Belt, about 30 – 55 times the distance the Earth is from the Sun are known as short period comets, and have periods less than 200 years. Halley’s comet is a well known short period comet, having a period of about 76 years. Note that the Kuiper belt starts at the orbit of the planet Neptune. (Yes, Pluto is a Kuiper Belt object!) (The average Earth-Sun distance is 93 million miles or 150 million km and has been established as a standard unit of distance in astronomy known as an Astronomical Unit or “AU”.)

Long period comets originate from a much more distant region of the solar system, the Oort Cloud. This cloud of frozen debris extends from 5,000 AU to 100,000 AU. Way out there! These comets can have periods as long as 30 million years to complete an orbit around the Sun. Comet Catalina most likely originated from here.

Catch a glimpse of comet Catalina if you can in January, as it will be on the edge of naked-eye visibility, so under the right conditions you won’t need binoculars or a telescope, but they will make for much better viewing. Comets are relics of the early solar system and the more we can study them, the more we learn about how our place in space has formed.


Jets on comet 67P from OSIRIS Imager on Rosetta – Image courtesy of the European Space Agency

Check out the European Space Agency’s site for amazing pictures and details on comet 67P (Churyumov-Gerasimenko) that their probe Rosetta has been flying in formation with for the last year.

Till next time,

RC Davison



A Day With No Night – “Starry Night” Wallpaper

Most wallpapers evolve from an idea, or something I’ve seen during my daily journey through life.  Starry Night actually started out as a desert scene and ended up with water and a whole lot of suns in the sky.

Wallpaper - Starry Night

Starry Night

The vast majority of stars in the Universe are made up of red dwarf stars or class M stars.  They are smaller and cooler than our Sun and because of the fact that they are dimmer and cooler, they consume their hydrogen fuel at a much lower rate.  This means that these stars are very long lived – on the order of 10 trillion years, as compared to our Sun, which will be around for about 10 billion years.

Red dwarfs typically exist as solitary stars, but stars that are brighter than the red dwarfs tend to be found more commonly in binary configurations.  A binary star system has two stars that orbit around a common center of mass.  Stars can also exist in three, four or more configurations, but as you add more stars to the mix, the more unstable the system becomes.  Planets can form in such multi-stellar systems and several have been uncovered by the Kepler mission.

Starry Night is a multi-stellar system.  The most interesting thing that occurred to me was that the inhabitants on a planet in such a system may never have a night sky with which to peer into the depths of the Universe!  Imagine how much they would never know about the Universe.  And, even more interesting is to consider their response when they manage to rise above their atmosphere and glimpse the cosmos for the first time.

Enjoy Starry Night and visit the ORBITAL MANEUVERS web site for additional wallpapers and more.

Till next time,

RC Davison

B612 Foundation: Searching for the Asteroid Threat


The B612 Foundation is an organization founded by Apollo astronaut Rusty Schweickart and Shuttle astronaut Ed Lu to identify asteroids that may be a threat to our planet Earth and develop the technology to prevent an impact. Pronounced: B – 6 – 12, the foundation is named after the planet in the story, THE LITTLE PRINCE, by Antoine de Saint-Exupery.

In ORBITAL MANEUVERS, the asteroid that impacts Earth was a rogue, passing through our solar system and escaping detection by the underfunded systems which were in place to find such objects. Part of the reason for writing the book was to bring to people’s attention the reality that we are not seeing everything that is out there and the consequences of that can be devastating to all life on this planet.

Meteor over Chelyabinsk, Russia. Credit: Nasha Gazeta newspaper

We had a close call on February 15, 2013. While we were watching asteroid 2012 DA14, a 150 foot (45 meter) hunk of rock fly by the Earth, a smaller asteroid (about 60 feet or 20 meters) blazed through the skies over Chelyabinsk, Russia. Fortunately it only injured about 1200 people and caused about $33 million in damages—it could have been a lot worse! What if it exploded at a lower altitude or impacted in a city…or was bigger?

The B612 Foundation looked at data that the military collected from 2000 to 2013 while monitoring for nuclear explosions and found 26 events that ranged in magnitude from 1 to 600 kilotons of TNT. These were not nuclear events but asteroids detonating in the atmosphere around the globe. The atomic bomb that destroyed Hiroshima at the end of World War II was 15 kilotons…the event over Chelyabinsk was about 600 kilotons. The most significant data gathered from this study is that asteroids large enough to destroy a city enter Earth’s atmosphere at a rate 3 to 10 times higher than were previously thought. The impact from a city-killer asteroid potentially can happen every 100 years. It could happen in 99 years; it could happen in the next minute.

This should be unsettling to anyone reading this. And, even more unsettling is the fact that we have technologies that we can use to prevent these impacts—as long as we have enough advanced warning—but this is not being aggressively pursued by the major governments on this planet. There are organizations like B612 with their Sentinel Mission to find and track asteroids and the Planetary Society’s Laser Bees, which will deflect threatening asteroids.

Check out the video and the B612 Foundation and the Planetary Society’s website for more information. If the major governments of the world aren’t interested in addressing this problem seriously, we can at least provide grassroots support to those groups that are taking on this responsibility.

Till next time,

RC Davison

An Amazing Model of Our Universe!


Astronomers, astrophysicists and cosmologists have a very difficult and frustrating life. They can’t touch the star, exoplanet, galaxy, nebula or other celestial object they are studying, nor can they send a probe as a surrogate to take a sample or direct measurement (aside from the few lucky planetary scientists who’ve had missions within our solar system). The topics of their interests lie at distances most people can’t even comprehend. They are restricted to study their subjects with light—infrared, visible, ultraviolet, x-rays, gamma rays and radio waves—that the objects emit or reflect light from another source.

Galactic cluster

Early formation of a galactic cluster along webs of dark matter – Credit: “Illustris Collaboration” / “Illustris Simulation”.

So how do they study these distant objects? They take pictures in light that ranges across the spectrum, and they gather the spectra of these objects. The spectra consist of the light emitted and/or reflected from the objects, broken down it into its constituent parts which indicates what elements are absorbing or emitting the light energy.

Absorption line spectra

Absorption line spectra

They then apply statistical analysis to the reams of data they’ve collected to try to understand and unlock the secrets of the cosmos. These scientists also create clever experiments and conduct observational surveys of the cosmos to provide them with data they can use to further develop their theories. And, they create models. They build computer models to test their theories and see if their models replicate or even come close to matching what they can see in the heavens above. These models are used to predict everything from stellar evolution, planetary atmospheres and black holes to galactic structures and clusters to name a few. There are those that aspire to reach even further. They want to model the evolution of the Universe from the dawn of the big bang to the present day.

A team lead by Mark Vogelsberger (MIT/Harvard-Smithsonian Center for Astrophysics) have done just that. They have developed a sophisticated model of a piece of the Universe (a cube about 326 million light-years (ly) on a side) that incorporates dark matter, as well as normal visible matter. The model, called Illustris, shows the evolution of the Universe from about 12 million years after the big bang to present day, and it maps out the cosmic webs of dark matter, along which normal visible matter collects. The amazing thing about this model is that they can zoom into it and display structures as small as galaxies like our Milky Way galaxy, which look like they could have been photographed by the Hubble telescope! These simulated galaxies exhibit similar chemistries to the galaxies we study today.

Galaxies created in Illustris

Collection of galaxies created in Illustris – Credit: “Illustris Collaboration” / “Illustris Simulation”

The team worked for over five years to develop this model, which incorporates over 12 billion 3D pixels to describe the sample of the Universe. If one were to try to run this simulation on a desktop computer, it would take over 2000 years to finish the calculations. Fortunately, the supercomputers used generated the simulation in 3 months of computer time. The end result contained over 41,000 galaxies embedded in the cosmic web of dark matter and visible matter.

Below is an amazing comparison of the Hubble eXtreme Deep Field image on the left and on the right side, an equivalent image produced by Illustris.

Hubble image vs Illustris image

Hubble Extreme Deep Field on the left and Illustris’ simulation on the right! Credit: “Illustris Collaboration” / “Illustris Simulation”

Take a look at the fascinating videos of this project: Nature – “A Virtual Universe” (narrated and about 4 minutes long) and a longer, unnarrated video “To Compute the Laws of Nature”. Also, check out the Illustris, website for more detailed information and additional images and videos.

Till next time,

RC Davison


(Note: If you visit the “arXiv” links for any of the references you should be able to view an earlier version of the published papers.)

A Game of Cosmic Hide and Seek


Playing hide and seek with my children when they were really little was always fun, especially in the beginning when they didn’t realize that I could see them when they covered themselves with a blanket or pillow. In a way, it’s similar with this image of the supernova remnant, DEM L241 located in the Large Magellanic Cloud, a small dwarf galaxy that orbits the Milky Way galaxy. The nebula is the result of a supernova which occurred in a binary star system. The star that is highlighted in the images below is the large companion star that survived the explosion of its partner, which now exists as a black hole or neutron star and is hidden from our view—almost.

Composite image of DEM L241

Composite image of the supernova remnant DEM L241 Image Credit: X-ray: NASA/CXC/SAO/F.Seward et al; Optical: NOAO/CTIO/MCELS, DSS

The above image shows a cloud of dust and gas with a dramatic swath of purple cutting across it. This is a composite image showing the view in the optical (visual) part of the spectrum and the same region in X-rays taken by the Chandra X-ray telescope. (See images below.) The large star of the pair is visible in the optical image and when we look at only the X-rays emitted from the region there is a bright dot in the same spot as the star – the black hole or neutron star hiding from us in the visible part of the spectrum. When these images are superimposed the black hole and the star align.

Optical Image of DEB L241

Optical image of DEM L241 Image credit: Optical: NOAO/CTIO/MCELS, DSS

X-ray image of DEM L241

X-ray image of the supernova remnant DEM L241 Image credit:NASA/CXC/SAO/F.Seward et al

What is remarkable is that this companion star survived the explosion of its partner. The super-dense companion gives itself away in X-rays because it is pulling in surrounding material, possibly from the nearby star, which gets heated to tens of millions of degrees by friction and radiates light in X-rays as a result. The progenitor star for the X-ray source was probably a super giant with a mass at least 25 times the mass of our Sun. The surviving super giant star and the black hole / neutron star orbit each other with a period on the order of tens of days, so they are fairly close together. More in-depth observations of the pair will help determine if the hidden companion is a black hole or a neutron star.

The surviving companion, being a super giant star, will eventually follow the same path as its partner and explode in a supernova, leaving behind a black hole or neutron star.  This newly transformed celestial body will dance a pas de deux with its old partner for billions of years as the light from the supernova eventually fades to black.

For more information check out the Chandra X-ray telescope’s website.

Till next time,

RC Davison