Moon halo by Rob Sparks. Taken in Tuscon, Arizona with a Canon 6D, Rokinon 14mm f/2.8 lens.
Have you ever looked up on a clear night and noticed there’s a complete ring around the Moon? In fact, if you look closely, the ring can have a rainbow appearance, with bright spots on either side, or above and below. What’s going on with the Moon and the atmosphere to cause this effect?
This ring surrounding the Moon is caused by the refraction of Moonlight (which is really reflected sunlight, of course) through ice crystals suspended in the upper atmosphere between 5-10 km in altitude. It doesn’t have to be winter, since the cold temperatures at high altitudes are below freezing any time of the year. Generally they’re seen with cirrus clouds; the thin, wispy clouds at high altitude.
The ice crystals themselves have a very consistent hexagonal shape, which means that any light passing through them will always refract light – or bend – at the same angle.
Path of rays in a hexagonal prism” by donalbein – Own work. Licensed under CC BY-SA 2.5 via Commons.Moonlight passes through one facet of the ice crystal, and is then refracted back out at exactly the angle of 22-degrees.
Of course, the atmosphere is filled with an incomprehensible number of crystals, all refracting moonlight off in different directions. But at any moment, a huge number happen to be in just the right position to be refracting light towards your eyes. You just aren’t in a position to see all the other refracted light. In fact, everyone sees their own private halo, because you’re only seeing the crystals that happen to be aligning the light for your specific location. Someone a few meters beside you is seeing their own private version of the halo – just like a rainbow.
A halo rings the bright moon and planet Jupiter (left of moon) Credit: Bob King
The size of the ring is most commonly 22-degrees. This is about the same size as your open hand on your outstretched arm. The Moon itself, for comparison, is the size of your smallest nail when you hold out your hand.
The 22-degree size corresponds to the refraction angle of moonlight.
We see a rainbow because the different colors are refracted at slightly different angles. This is exactly what happens with a rainbow. The moonlight is broken up into its separate colors because they all refract at different angles, and so you see the colors split up like a rainbow.
Lunar halo with rainbow. Photo credit: Gustav Sanchez.Moon dogs (or “mock moons”) are seen as bright spots that can appear on either side of the Moon, when the Moon is closer to the horizon, and at its fullest. These are located on either side of the lunar ring, parallel to the horizon.
In certain conditions, especially in the Arctic, where the ice crystals can be close to the surface, you can get a moon pillar. The light from the Moon reflects off the ice crystals near the surface, creating a glow near the horizon. This is a Sun pillar (not a moon pillar), but it’s the same general idea. Photo credit: Mary Spicer.
Want to see more? Here’s a great lunar halo photo from NASA’s APOD. And here’s more info from Earth and Sky.
This road near Phoenix, Arizona leads to the heart of the Milky Way. Well, that’s assuming your car will handle the 26,000 light-year drive, and can fly through, uh, space. And you can endure the cold, radiation and space madness. Anyway, you get the metaphor.
Tyler Sichelski took this photo of the galactic core, the central bulge of the Milky Way. It’s a region of incredible density and activity, and at the very heart, hidden from our view is the Milky Way’s supermassive black hole, with 4 million times the mass of the Sun. Within a parsec’s distance of this black hole, there are thousands of old, main-sequence stars as well as some of the hottest, brightest stars around.
Path by Tyler Sichelski
Unfortunately, we can’t actually see the center of the galaxy because of the gas and dust that obscures our view. And in this photograph, you can actually see the dark dust lanes and regions. Many of the nebulae you’re familiar with are in this picture, like the Lagoon Nebula, the Omega Nebula and the Trifid Nebula. In fact, it’s hard to know where one nebula ends, and the next one starts.
Tyler used a Canon 6D camera with a 16-28mm f/2.8 lens. He took 10 separate exposures of the sky and then stacked them up in Photoshop.
Of course, you should check out more of Tyler’s photographs at the Universe Today Flickr photo pool (nearly 2,000 members and 33,000 photographs now). This is a place where astrophotographers share their photos of the night sky, and then we reshare them on our website and across our social media.
New research indicates that eccentric orbits may play a role in planet habitability. Credit: NASA Ames, SETI Institute, JPL-Caltech, T. Pyle)
In 1950, physicist Enrico Fermi raised a very important question about the Universe and the existence of extraterrestrial life. Given the size and age of the Universe, he stated, and the statistical probability of life emerging in other solar systems, why is it that humanity has not seen any indications of intelligent life in the cosmos? This query, known as the Fermi Paradox, continues to haunt us to this day.
If, indeed, there are billions of star systems in our galaxy, and the conditions needed for life are not so rare, then where are all the aliens? According to a recent paper by researchers at Australian National University’s Research School of Earth Sciences., the answer may be simple: they’re all dead. In what the research teams calls the “Gaian Bottleneck”, the solution to this paradox may be that life is so fragile that most of it simply doesn’t make it.
The waning crescent Moon above Venus and Saturn (dimmer and below Venus) in the dawn twilight on January 6, 2016. The Moon re-visits the grouping in early February. Image credit and copyright: Alan Dyer.
A fine sight greets early risers this week into the month of February, as all five naked eye planets: Mercury, Venus, Mars, Saturn and Jupiter ring the sky from horizon to horizon.
Though not a true planetary alignment as extolled by many websites, this is a great chance to see all five classical planets above the horizon at once… or seven, if you count the waning gibbous Moon and the rising Sun, as the ancients did as part of their geocentric, Earth-entered universe. You can kinda see how they got there, as the very heavens themselves seemed to whorl about the cradle of earthly human affairs. Continue reading “And Mercury Makes Five: See All Naked Eye Planets in the Sky at Once”
Artist's concept of the hypothetical "Planet Nine." Could it have moons? Credit: NASA/JPL-Caltech/Robert Hurt
Artistic rendering shows the distant view from theoretical Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Credit: Caltech/R. Hurt (IPAC)
The astronomer known worldwide for vigorously promoting the demotion of Pluto from its decades long perch as the 9th Planet, has now found theoretical evidence for a new and very distant gas giant planet lurking way beyond Pluto out to the far reaches of our solar system.
Planets and other objects in our Solar System. Credit: NASA.
Here on Earth, we tend to take time for granted, never suspected that the increments with which we measure it are actually quite relative. The ways in which we measure our days and years, for example, are actually the result of our planet’s distance from the Sun, the time it takes to orbit, and the time it takes to rotate on its axis. The same is true for the other planets in our Solar System.
While we Earthlings count on a day being about 24 hours from sunup to sunup, the length of a single day on another planet is quite different. In some cases, they are very short, while in others, they can last longer than years – sometimes considerably! Let’s go over how time works on other planets and see just how long their days can be, shall we?
A Day On Mercury:
Mercury is the closest planet to our Sun, ranging from 46,001,200 km at perihelion (closest to the Sun) to 69,816,900 km at aphelion (farthest). Since it takes 58.646 Earth days for Mercury to rotate once on its axis – aka. its sidereal rotation period – this means that it takes just over 58 Earth days for Mercury to experience a single day.
However, this is not to say that Mercury experiences two sunrises in just over 58 days. Due to its proximity to the Sun and rapid speed with which it circles it, it takes the equivalent of 175.97 Earth days for the Sun to reappear in the same place in the sky. Hence, while the planet rotates once every 58 Earth days, it is roughly 176 days from one sunrise to the next on Mercury.
Images of Mercury’s northern polar region, provided by MESSENGER. Credit: NASA/JPL
What’s more, it only takes Mercury 87.969 Earth days to complete a single orbit of the Sun (aka. its orbital period). This means a year on Mercury is the equivalent of about 88 Earth days, which in turn means that a single Mercurian (or Hermian) year lasts just half as long as a Mercurian day.
What’s more, Mercury’s northern polar regions are constantly in the shade. This is due to it’s axis being tilted at a mere 0.034° (compared to Earth’s 23.4°), which means that it does not experience extreme seasonal variations where days and nights can last for months depending on the season. On the poles of Mercury, it is always dark and shady. So you could say the poles are in a constant state of twilight.
A Day On Venus:
Also known as “Earth’s Twin”, Venus is the second closest planet to our Sun – ranging from 107,477,000 km at perihelion to 108,939,000 km at aphelion. Unfortunately, Venus is also the slowest moving planet, a fact which is made evident by looking at its poles. Whereas every other planet in the Solar System has experienced flattening at their poles due to the speed of their spin, Venus has experienced no such flattening.
Venus has a rotational velocity of just 6.5 km/h (4.0 mph) – compared to Earth’s rational velocity of 1,670 km/h (1,040 mph) – which leads to a sidereal rotation period of 243.025 days. Technically, it is -243.025 days, since Venus’ rotation is retrograde. This means that Venus rotates in the direction opposite to its orbital path around the Sun.
The planet Venus, as imagined by the Magellan 10 mission. Credit: NASA/JPL
So if you were above Venus’ north pole and watched it circle around the Sun, you would see it is moving clockwise, whereas its rotation is counter-clockwise. Nevertheless, this still means that Venus takes over 243 Earth days to rotate once on its axis. However, much like Mercury, Venus’ orbital speed and slow rotation means that a single solar day – the time it takes the Sun to return to the same place in the sky – lasts about 117 days.
So while a single Venusian (or Cytherean) year works out to 224.701 Earth days, it experiences less than two full sunrises and sunsets in that time. In fact, a single Venusian/Cytherean year lasts as long as 1.92 Venusian/Cytherean days. Good thing Venus has other things in common With Earth, because it is sure isn’t its diurnal cycle!
A Day On Earth:
When we think of a day on Earth, we tend to think of it as a simple 24 hour interval. In truth, it takes the Earth exactly 23 hours 56 minutes and 4.1 seconds to rotate once on its axis. Meanwhile, on average, a solar day on Earth is 24 hours long, which means it takes that amount of time for the Sun to appear in the same place in the sky. Between these two values, we say a single day and night cycle lasts an even 24.
At the same time, there are variations in the length of a single day on the planet based on seasonal cycles. Due to Earth’s axial tilt, the amount of sunlight experienced in certain hemispheres will vary. The most extreme case of this occurs at the poles, where day and night can last for days or months depending on the season.
At the North and South Poles during the winter, a single night can last up to six months, which is known as a “polar night”. During the summer, the poles will experience what is called a “midnight sun”, where a day lasts a full 24 hours. So really, days are not as simple as we like to imagine. But compared to the other planets in the Solar System, time management is still easier here on Earth.
A Day On Mars:
In many respects, Mars can also be called “Earth’s Twin”. In addition to having polar ice caps, seasonal variations , and water (albeit frozen) on its surface, a day on Mars is pretty close to what a day on Earth is. Essentially, Mars takes 24 hours 37 minutes and 22 seconds to complete a single rotation on its axis. This means that a day on Mars is equivalent to 1.025957 days.
The seasonal cycles on Mars, which are due to it having an axial tilt similar to Earth’s (25.19° compared to Earth’s 23.4°), are more similar to those we experience on Earth than on any other planet. As a result, Martian days experience similar variations, with the Sun rising sooner and setting later in the summer and then experiencing the reverse in the winter.
However, seasonal variations last twice as long on Mars, thanks to Mars’ being at a greater distance from the Sun. This leads to the Martian year being about two Earth years long – 686.971 Earth days to be exact, which works out to 668.5991 Martian days (or Sols). As a result, longer days and longer nights can be expected last much longer on the Red Planet. Something for future colonists to consider!
Sunrise at Gale Crater on Mars. Gale is at center top with the mound in the middle, called Mt. Sharp (Aeolis Mons.)
A Day On Jupiter:
Given the fact that it is the largest planet in the Solar System, one would expect that a day on Jupiter would last a long time. But as it turns out, a Jovian day is officially only 9 hours, 55 minutes and 30 seconds long, which means a single day is just over a third the length of an Earth day. This is due to the gas giant having a very rapid rotational speed, which is 12.6 km/s (45,300 km/h, or 28148.115 mph) at the equator. This rapid rotational speed is also one of the reasons the planet has such violent storms.
Note the use of the word officially. Since Jupiter is not a solid body, its upper atmosphere undergoes a different rate of rotation compared to its equator. Basically, the rotation of Jupiter’s polar atmosphere is about 5 minutes longer than that of the equatorial atmosphere. Because of this, astronomers use three systems as frames of reference.
System I applies from the latitudes 10° N to 10° S, where its rotational period is the planet’s shortest, at 9 hours, 50 minutes, and 30 seconds. System II applies at all latitudes north and south of these; its period is 9 hours, 55 minutes, and 40.6 seconds. System III corresponds to the rotation of the planet’s magnetosphere, and it’s period is used by the IAU and IAG to define Jupiter’s official rotation (i.e. 9 hours 44 minutes and 30 seconds)
Jupiter and Io capturing the Sun. Image Credit: NASA/JPL
So if you could, theoretically, stand on the cloud tops of Jupiter (or possibly on a floating platform in geosynchronous orbit), you would witness the sun rising an setting in the space of less than 10 hours from any latitude. And in the space of a single Jovian year, the sun would rise and set a total of about 10,476 times.
A Day On Saturn:
Saturn’s situation is very similar to that of Jupiter’s. Despite its massive size, the planet has an estimated rotational velocity of 9.87 km/s (35,500 km/h, or 22058.677 mph). As such Saturn takes about 10 hours and 33 minutes to complete a single sidereal rotation, making a single day on Saturn less than half of what it is here on Earth. Here too, this rapid movement of the atmosphere leads to some super storms, not to mention the hexagonal pattern around the planet’s north pole and a vortex storm around its south pole.
And, also like Jupiter, Saturn takes its time orbiting the Sun. With an orbital period that is the equivalent of 10,759.22 Earth days (or 29.4571 Earth years), a single Saturnian (or Cronian) year lasts roughly 24,491 Saturnian days. However, like Jupiter, Saturn’s atmosphere rotates at different speed depending on latitude, which requires that astronomers use three systems with different frames of reference.
System I encompasses the Equatorial Zone, the South Equatorial Belt and the North Equatorial Belt, and has a period of 10 hours and 14 minutes. System II covers all other Saturnian latitudes, excluding the north and south poles, and have been assigned a rotation period of 10 hr 38 min 25.4 sec. System III uses radio emissions to measure Saturn’s internal rotation rate, which yielded a rotation period of 10 hr 39 min 22.4 sec.
This portrait looking down on Saturn and its rings was created from images obtained by NASA’s Cassini spacecraft on Oct. 10, 2013. Credit: NASA/JPL-Caltech/Space Science Institute/G. Ugarkovic
Using these various systems, scientists have obtained different data from Saturn over the years. For instance, data obtained during the 1980’s by the Voyager 1 and 2 missions indicated that a day on Saturn was 10 hours 39 minutes and 24 seconds long. In 2004, data provided by the Cassini-Huygens space probe measured the planet’s gravitational field, which yielded an estimate of 10 hours, 45 minutes, and 45 seconds (± 36 sec).
In 2007, this was revised by researches at the Department of Earth, Planetary, and Space Sciences, UCLA, which resulted in the current estimate of 10 hours and 33 minutes. Much like with Jupiter, the problem of obtaining accurate measurements arises from the fact that, as a gas giant, parts of Saturn rotate faster than others.
A Day On Uranus:
When we come to Uranus, the question of how long a day is becomes a bit complicated. One the one hand, the planet has a sidereal rotation period of 17 hours 14 minutes and 24 seconds, which is the equivalent of 0.71833 Earth days. So you could say a day on Uranus lasts almost as long as a day on Earth. It would be true, were it not for the extreme axial tilt this gas/ice giant has going on.
With an axial tilt of 97.77°, Uranus essentially orbits the Sun on its side. This means that either its north or south pole is pointed almost directly at the Sun at different times in its orbital period. When one pole is going through “summer” on Uranus, it will experience 42 years of continuous sunlight. When that same pole is pointed away from the Sun (i.e. a Uranian “winter”), it will experience 42 years of continuous darkness.
Uranus as seen by NASA’s Voyager 2. Credit: NASA/JPL
Hence, you might say that a single day – from one sunrise to the next – lasts a full 84 years on Uranus! In other words, a single Uranian day is the same amount of time as a single Uranian year (84.0205 Earth years).
In addition, as with the other gas/ice giants, Uranus rotates faster at certain latitudes. Ergo, while the planet’s rotation is 17 hours and 14.5 minutes at the equator, at about 60° south, visible features of the atmosphere move much faster, making a full rotation in as little as 14 hours.
A Day On Neptune:
Last, but not least, we have Neptune. Here too, measuring a single day is somewhat complicated. For instance, Neptune’s sidereal rotation period is roughly 16 hours, 6 minutes and 36 seconds (the equivalent of 0.6713 Earth days). But due to it being a gas/ice giant, the poles of the planet rotate faster than the equator.
Whereas the planet’s magnetic field has a rotational speed of 16.1 hours, the wide equatorial zone rotates with a period of about 18 hour. Meanwhile, the polar regions rotate the fastest, at a period of 12 hours. This differential rotation is the most pronounced of any planet in the Solar System, and it results in strong latitudinal wind shear.
Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL
In addition, the planet’s axial tilt of 28.32° results in seasonal variations that are similar to those on Earth and Mars. The long orbital period of Neptune means that the seasons last for forty Earth years. But because its axial tilt is comparable to Earth’s, the variation in the length of its day over the course of its long year is not any more extreme.
As you can see from this little rundown of the different planets in our Solar System, what constitutes a day depends entirely on your frame of reference. In addition to it varying depending on the planet in question, you also have to take into account seasonal cycles and where on the planet the measurements are being taken from.
As Einstein summarized, time is relative to the observer. Based on your inertial reference frame, its passage will differ. And when you are standing on a planet other than Earth, your concept of day and night, which is set to Earth time (and a specific time zone) is likely to get pretty confused!
The waxing gibbous Moon closes in on Aldebaran (lower left). Image credit and copyright: Sarah & Simon Fisher
They braved the cold, cursed the clouds, wrestled with frozen telescope focusers and more, as dedicated astros worked to catch the first occultation of the bright star Aldebaran for 2016 by the waxing gibbous Moon.
Diagram of J.J. Thomson's "Plum Pudding Model" of the atom. Credit: boundless.com
Ever since it was first proposed by Democritus in the 5th century BCE, the atomic model has gone through several refinements over the past few thousand years. From its humble beginnings as an inert, indivisible solid that interacts mechanically with other atoms, ongoing research and improved methods have led scientists to conclude that atoms are actually composed of even smaller particles that interact with each other electromagnetically.
This was the basis of the atomic theory devised by English physicist J.J. Thompson in the late 19th an early 20th centuries. As part of the revolution that was taking place at the time, Thompson proposed a model of the atom that consisted of more than one fundamental unit. Based on its appearance, which consisted of a “sea of uniform positive charge” with electrons distributed throughout, Thompson’s model came to be nicknamed the “Plum Pudding Model”.
Though defunct by modern standards, the Plum Pudding Model represents an important step in the development of atomic theory. Not only did it incorporate new discoveries, such as the existence of the electron, it also introduced the notion of the atom as a non-inert, divisible mass. Henceforth, scientists would understand that atoms were themselves composed of smaller units of matter and that all atoms interacted with each other through many different forces.
Atomic Theory to the 19th century:
The earliest known examples of atomic theory come from ancient Greece and India, where philosophers such as Democritus postulated that all matter was composed of tiny, indivisible and indestructible units. The term “atom” was coined in ancient Greece and gave rise to the school of thought known as “atomism”. However, this theory was more of a philosophical concept than a scientific one.
Various atoms and molecules as depicted in John Dalton’s A New System of Chemical Philosophy (1808). Credit: Public Domain
It was not until the 19th century that the theory of atoms became articulated as a scientific matter, with the first evidence-based experiments being conducted. For example, in the early 1800s, English scientist John Dalton used the concept of the atom to explain why chemical elements reacted in certain observable and predictable ways.
Dalton began with the question of why elements reacted in ratios of small whole numbers and concluded that these reactions occurred in whole-number multiples of discrete units – i.e. atoms. Through a series of experiments involving gases, Dalton went on to develop what is known as Dalton’s Atomic Theory. This theory expanded on the laws of conversation of mass and definite proportions – formulated by the end of the 18th century – and remains one of the cornerstones of modern physics and chemistry.
The theory comes down to five premises: elements, in their purest state, consist of particles called atoms; atoms of a specific element are all the same, down to the very last atom; atoms of different elements can be told apart by their atomic weights; atoms of elements unite to form chemical compounds; atoms can neither be created or destroyed in chemical reaction, only the grouping ever changes.
By the late 19th century, scientists also began to theorize that the atom was made up of more than one fundamental unit. However, most scientists ventured that this unit would be the size of the smallest known atom – hydrogen. By the end of the 19th century, the situation would change drastically.
Lateral view of a sort of a Crookes tube with a standing cross. Credit: Wikimedia Commons/D-Kuru
Thompson’s Experiments:
Sir Joseph John Thomson (aka. J.J. Thompson) was an English physicist and the Cavendish Professor of Physics at the University of Cambridge from 1884 onwards. During the 1880s and 1890s, his work largely revolved around developing mathematical models for chemical processes, the transformation of energy in mathematical and theoretical terms, and electromagnetism.
However, by the late 1890s, he began conducting experiments using a cathode ray tube known as the Crookes’ Tube. This consists of a sealed glass container with two electrodes that are separated by a vacuum. When voltage is applied across the electrodes, cathode rays are generated (which take the form of a glowing patch of gas that stretches to the far end of the tube).
Through experimentation, Thomson observed that these rays could be deflected by electric and magnetic fields. He concluded that rather than being composed of light, they were made up of negatively charged particles he called “corpuscles”. Upon measuring the mass-to-charge ration of these particles, he discovered that they were 1ooo times smaller and 1800 times lighter than hydrogen.
This effectively disproved the notion that the hydrogen atom was the smallest unit of matter, and Thompson went further to suggest that atoms were divisible. To explain the overall charge of the atom, which consisted of both positive and negative charges, Thompson proposed a model whereby the negatively charged corpuscles were distributed in a uniform sea of positive charge.
A depiction of the atomic structure of the helium atom. Credit: Creative Commons
These corpuscles would later be named “electrons”, based on the theoretical particle predicted by Anglo-Irish physicist George Johnstone Stoney in 1874. And from this, the Plum Pudding Model was born, so named because it closely resembled the English desert that consists of plum cake and raisins. The concept was introduced to the world in the March 1904 edition of the UK’sPhilosophical Magazine, to wide acclaim.
Problems With the Plum Pudding Model:
Unfortunately, subsequent experiments revealed a number of scientific problems with the model. For starters, there was the problem of demonstrating that the atom possessed a uniform positive background charge, which came to be known as the “Thomson Problem”. Five years later, the model would be disproved by Hans Geiger and Ernest Marsden, who conducted a series of experiments using alpha particles and gold foil.
In what would come to be known as the “gold foil experiment“, they measured the scattering pattern of the alpha particles with a fluorescent screen. If Thomson’s model were correct, the alpha particles would pass through the atomic structure of the foil unimpeded. However, they noted instead that while most shot straight through, some of them were scattered in various directions, with some going back in the direction of the source.
Geiger and Marsden concluded that the particles had encountered an electrostatic force far greater than that allowed for by Thomson’s model. Since alpha particles are just helium nuclei (which are positively charged) this implied that the positive charge in the atom was not widely dispersed, but concentrated in a tiny volume. In addition, the fact that those particles that were not deflected passed through unimpeded meant that these positive spaces were separated by vast gulfs of empty space.
The anticipated results of the Gieger-Marsden experiment (left), and the actual results (right). Credit: Wikimedia Commons/Kurzon
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By 1911, physicist Ernest Rutherford interpreted the Geiger-Marsden experiments and rejected Thomson’s model of the atom. Instead, he proposed a model where the atom consisted of mostly empty space, with all its positive charge concentrated in its center in a very tiny volume, that was surrounded by a cloud of electrons. This came to be known as the Rutherford Model of the atom.
Subsequent experiments by Antonius Van den Broek and Neils Bohr refined the model further. While Van den Broek suggested that the atomic number of an element is very similar to its nuclear charge, the latter proposed a Solar-System-like model of the atom, where a nucleus contains the atomic number of positive charge and is surrounded by an equal number of electrons in orbital shells (aka. the Bohr Model).
Though it would come to be discredited in just five years time, Thomson’s “Plum Pudding Model” would prove to be a crucial step in the development of the Standard Model of particle physics. His work in determining that atom’s were divisible, as well as the existence of electromagnetic forces within the atom, would also prove to be major influence on the field of quantum physics.
Now you see it... the December 23rd 2015 occultation of Aldebaran. Image credit and copyright: Roger Hutchinson
“That’s no moon…”
But in this case, it is (sorry Ben), and that Moon is headed to temporarily obliterate (occult) the view of the bright star Aldebaran as seen from the Earth on the evening of January 19th and into the morning of the 20th.
Here are the specifics. Not to be confused with Princess Leia’s homeworld of Alderaan of Star Wars science fiction fame, the occultation of the bright star Aldebaran in the astronomical constellation Taurus occurs on the night of Tuesday, January 19th and finds the waxing gibbous the Moon 82% illuminated and four days from the first Full Moon of the year on January 24th. This is also the first of 13 occultations of Aldebaran for the year 2016, one for even lunation. Evening occultations are particularly favorable, as the star in question always disappears along the leading edge dark limb of the Moon, to reappear along its daytime limb. Once the Moon is waning, the reverse is true, as the bright limb then leads towards New phase.
We’ve caught occultations of bright stars very near Full, and can attest that it is indeed possible to follow a +1st magnitude star all the way to the lunar limb.
The occultation footprint for tomorrow night’s event. Image credit: Occult 4.2
The occultation footprint runs across the nighttime northern hemisphere from the early morning hours in western Europe and the United Kingdom across the northern Atlantic, across the contiguous ‘lower 48’ states of of U.S. to Canada and northern Mexico. It actually juuuust misses us here down in sunny Florida, one of the few states that will miss out on the event. This is the best placed occultation of Aldebaran for 2016 for most North American viewers, falling during early evening prime time hours high in the post twilight sky.
Here’s the timing for the ingress (beginning) and egress (end) for the occultation for selected cities; the International Occultation Timing Association (IOTA) has an extensive table of times for cities within the occultation path. (all quoted using Universal Time(UT), plus altitude (alt) in degrees (deg) :
London
Ingress: 3:25 UT/alt: 6 deg
Egress: 3:57 UT/alt: 2 deg
Atlanta
Ingress: 2:22 UT/73 deg
Egress: 3:06 UT/70 deg
Boston
Ingress: 2:35 UT/60 deg
Egress: 3:47 UT/50 deg
The occultation as seen from Boston Mass. Image credit: Starry Night Edu.
Los Angeles
Ingress: 1:05 UT/40 deg
Egress: 2:13 UT/54 deg
Montreal
Ingress: 2:28 UT/59 deg
Egress: 3:42 UT/51 deg
Halifax
Ingress: 2:46 UT/53 deg
Egress: 3:57 UT/43 deg
Note that precise times for the event change slightly due to the position of the observer within various time zones, as well as the parallax shift of the Moon as seen from the Earth.
Occultations always give us a chance to analyze the target star for any possible close in binary companions, as the star winks out in a tell tale step-wise fashion. Aldebaran has no known close companion star, though spurious claims have been made for planets orbiting the star over the years. 65 light years distant, Aldebaran is in the direction of the Hyades star cluster in the distant galactic background, though it is physically unrelated to the group, which is 153 light years from the Earth. This also means that several bright stars in the Hyades get occulted by the Moon as well on Tuesday night, as the Moon makes its way to Aldebaran and its date with astronomical destiny.
The lunar limb profile along the graze line. Image credit: Brad Timerson/IOTA
An occultation of a bright star by the Moon also allows selenographers to map out the profile of the jagged lunar limb, as light from the distant star is alternately shines through the valleys and is occluded mountain peaks along the edge of the relatively nearby Moon. This effect can be especially dramatic for observers positioned along the graze line, which on Tuesday night runs from southern Georgia through southern Texas into northern Mexico, across to Baja California.
The southern graze line for tomorrow night’s event. Image credit: IOTA/Google Maps
Recording the occultation is as simple as aiming a video camera coupled to a telescope at the Moon at the appointed time, and running video. Start early, and you may want to overexpose the waxing gibbous Moon a bit to bring out Aldebaran. We managed to nab the 2008 occultation of Antares by the nearly Full Moon using a simple JVC video camera and an 8” Schmidt-Cassegrain telescope.
The event will be easily visible using binoculars, and should even be noticeable to the unaided eye.
That’s it for this week in ‘things passing in front of each other…’ In astronomy, lots can be learn just from analyzing light, or in this case, the absence of it. What good are occultations? Well, they might just save your not-so-secret rebel base from immediate annihilation:
the gas giant world Yavin occults the moon housing the rebel base in Star Wars Episode IV. Image credit: Lucasfilm ltd.
And watch that Moon, as there will be another good occultation of Aldebaran shifted just slightly westward next lunation on February 16th, 2016.
What would Earth look like if it had a ring system like Saturn's. Credit: Kevin Gill/Flickr
Saturn’s Rings are amazing to behold. Since they were first observed by Galileo in 1610, they have been the subject of endless scientific interest and popular fascination. Composed of billions of particles of dust and ice, these rings span a distance of about 282,000 km (175,000 miles) – which is three quarters of the distance between the Earth and its Moon – and hold roughly 30 quintillion kilograms (that’s 3.0. x 1018 kg) worth of matter.
All of the Solar System’s gas giants, from Jupiter to Neptune, have their own ring system – albeit less visible and picturesque ones. Sadly, none of the terrestrial planets (i.e. Mercury, Venus, Earth and Mars) have such a system. But just what would it look like if Earth did? Putting aside the physical requirements that it would take for a ring system to exist, what would it be like to look up from Earth and see beautiful rings reaching overhead?
