What’s up with the Sun? As we’ve said previous, what the Sun isn’t doing is the big news of 2018 in solar astronomy. Now, the Sun sent us another curveball this past weekend, with the strange tale of growing sunspot AR 2720.
Are you keeping a eye on Jupiter? The King of the Planets, Jove presents a swirling upper atmosphere full of action, a worthy object of telescopic study as it heads towards another fine opposition on May 9th, 2018.
Now, an interesting international study out of the School of Engineering in Bilbao, Spain, the Astronomical Society of France, the Meath Astronomical Group in Dublin Ireland, the Astronomical Society of Australia, and the Esteve Duran Observatory in Spain gives us a fascinating and encouraging possibly, and another reason to keep a sharp eye on old Jove: Jupiter may just get smacked with asteroids on a more regular basis than previously thought.
The study is especially interesting, as it primarily focused in on flashes chronicled by amateur imagers and observers in recent years. In particular, researchers focused on impact events witnessed on March 17th 2016 and May 26th, 2017, along with the comparison of exogenous (of cosmic origin) dust measured in the upper atmosphere. This allowed researchers to come up with an interesting estimate: Jupiter most likely gets hit by an asteroid 5-20 meters in diameter (for comparison, the Chelyabinsk bolide was an estimated 20 meters across) 10 to 65 times every year, though researchers extrapolate that a dedicated search might only nab an impact flash or scar once every 0.4 to 2.4 years or so.
Compare this impact rate with the Earth, which gets hit by a Chelyabinsk-sized 20-meter impactor about once every half century or so. Incidentally, we know this impact rate on Earth better than ever before, largely due to U.S. Department of Defense classified assets in space continually watching for nuclear tests and missile launches, which also pick up an occasional meteor “photobomb.”
One reason we may never have witnessed a meteor impact on Jupiter is, astronomers (both professional and amateur) never thought to look for them. The big wake-up call was the impact of Comet Shoemaker-Levy 9 in July 1994, an event witnessed by the newly refurbished Hubble Space Telescope as the resulting impact scars were easily visible in backyard telescopes for weeks afterward. Back in the day, speculation was rampant in the days leading up to the impact: would the collision be visible at all? Or would gigantic Jupiter simply gobble up the tiny comet fragments with nary a belch?
Australian amateur astronomer Anthony Wesley also caught an interesting impact (scar?) in 2009, and every few years or so, we get word of an elusive flash reported on the Jovian cloudtops, sometimes corroborated by a secondary independent observation or a resulting impact scar, and sometimes not.
Of course, there are factors which will lower said ideal versus the actual observed impact rate. There’s always a month or so a year, for example, when Jupiter is near solar conjunction on the far side of the Sun, and out of range for observation. Also, we only see half of the Jovian disk from our Earthly perspective at any given time, and we’re about to lose our only set of eyes in orbit around Jupiter – NASA’s Juno spacecraft – later this summer, unless there’s a last minute mission extension.
On the plus side, however, Jupiter is a fast rotator, spinning on its axis once every 9.9 hours. This also means that near opposition, you can also track Jupiter through one full rotation in a single evening.
Then there’s the planet’s location in the sky: Currently, Jupiter’s crossing the southern constellation of Libra, and opposition for Jove moves about one astronomical constellation eastward along the ecliptic a year. Jupiter will bottom out along the ecliptic in late 2019, and won’t pop back up north of the celestial equator until May 2022. And while it’s not impossible for northern observers to keep tabs on Jupiter when it’s down south, we certainly get more gaps in coverage around this time.
Should we hail Jove as a protective ‘cosmic goal-tender,’ or fear it as the bringer of death and destruction? There are theories that Jupiter may be both: for example, Jupiter altered the inbound path of Comet Hale-Bopp in 1997, shortening its orbital period from 4,200 to 2,533 years. The 2000 book Rare Earth even included the hypothesis of Jupiter as a cosmic debris sweeper as one of the factors for why life evolved on Earth… if this is true, it’s an imperfect one, as Earth does indeed still get hit as well.
All reasons to keep an eye on Jupiter in the 2018 opposition season.
-See something strange? The ALPO Jupiter observers section wants to know!
Beneath the Antarctic ice sheet, there lies a continent that is covered by rivers and lakes, the largest of which is the size of Lake Erie. Over the course of a regular year, the ice sheet melts and refreezes, causing the lakes and rivers to periodically fill and drain rapidly from the melt water. This process makes it easier for Antarctica’s frozen surface to slide around, and to rise and fall in some places by as much as 6 meters (20 feet).
According to a new study led by researchers from NASA’s Jet Propulsion Laboratory, there may be a mantle plume beneath the area known as Marie Byrd Land. The presence of this geothermal heat source could explain some of the melting that takes place beneath the sheet and why it is unstable today. It could also help explain how the sheet collapsed rapidly in the past during previous periods of climate change.
The study, titled “Influence of a West Antarctic mantle plume on ice sheet basal conditions“, recently appeared in the Journal of Geophysical Research: Solid Earth. The research team was led by Helene Seroussi of the Jet Propulsion Laboratory, with support from researchers from the Department of Earth and Planetary Sciences at Washington University and the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research in Germany.
The motion of Antarctica’s ice sheet over time has always been a source of interest to Earth scientists. By measuring the rate at which the ice sheet rises and falls, scientists are able to estimate where and how much water is melting at the base. It is because of these measurements that scientists first began to speculate about the presence of heat sources beneath Antarctica’s frozen surface.
The proposal that a mantle plume exists under Marie Byrd Land was first made 30 years ago by Wesley E. LeMasurier, a scientist from the University of Colorado Denver. According to the research he conducted, this constituted a possible explanation for regional volcanic activity and a topographic dome feature. But it was only more recently that seismic imaging surveys offered supporting evidence for this mantle plume.
However, direct measurements of the region beneath Marie Byrd Land is not currently possible. Hence why Seroussi and Erik Ivins of the JPL relied on the Ice Sheet System Model (ISSM) to confirm the existence of the plume. This model is essentially a numerical depiction of the physics of the ice sheet, which was developed by scientists at the JPL and the University of California, Irvine.
To ensure that the model was realistic, Seroussi and her team drew on observations of changes in altitude of the ice sheet made over the course of many years. These were conducted by NASA’s Ice, Clouds, and Land Elevation Satellite (ICESat) and their airborne Operation IceBridge campaign. These missions have been measuring the Antarctic ice sheet for years, which have led tot he creation of very accurate three-dimensional elevation maps.
Seroussi also enhanced the ISSM to include natural sources of heating and heat transport that result in freezing, melting, liquid water, friction, and other processes. This combined data placed powerful constrains on the allowable melt rates in Antarctica, and allowed the team to run dozens of simulations and test a wide range of possible locations for the mantle plume.
What they found was that the heat flux caused by the mantle plume would not exceed more than 150 milliwatts per square meter. By comparison, regions where there is no volcanic activity typically experience a feat flux of between 40 and 60 milliwatts, whereas geothermal hotspots – like the one under Yellowstone National Park – experience an average of about 200 milliwatts per square meter.
Where they conducted simulations that exceeded 150 millwatts per square meter, the melt rate was too high compared to the space-based data. Except in one location, which was an area inland of the Ross Sea, which is known to experience intense flows of water. This region required a heat flow of at least 150 to 180 milliwatts per square meter to align with its observed melt rates.
In this region, seismic imaging has also shown that heating might reach the ice sheet through a rift in the Earth’s mantle. This too is consistent with a mantle plume, which are thought to be narrow streams of hot magma rising through the Earth’s mantle and spreading out under the crust. This viscous magma then balloons under the crust and causes it to bulge upward.
Where ice lies over top of the plume, this process transfers heat into the ice sheet, triggering significant melting and runoff. In the end, Seroussi and her colleagues provide compelling evidence – based on a combination of surface and seismic data – for a surface plume beneath the ice sheet of West Antarctica. They also estimate that this mantle plume formed roughly 50 to 110 million years ago, long before the West Antarctic ice sheet came into existence.
Roughly 11,000 years ago, when the last ice age ended, the ice sheet experienced a period of rapid, sustained ice loss. As global weather patterns and rising sea levels began to change, warm water was pushed closer to the ice sheet. Seroussi and Irvins study suggests that the mantle plume could be facilitating this kind of rapid loss today, much as it did during the last onset of an inter-glacial period.
Understanding the sources of ice sheet loss under West Antarctica is important as far as estimating the rate at which ice may be lost there, which is essentially to predicting the effects of climate change. Given that Earth is once again going through global temperature changes – this time, due to human activity – it is essential to creating accurate climate models that will let us know how rapidly polar ice will melt and sea levels will rise.
It also informs our understanding of how our planet’s history and climate shifts are linked, and what effect these had on its geological evolution.
Sixty-six million years ago, an asteroid struck Earth in what is now the Yucatan Peninsula in southern Mexico. This event, known as the Chicxulub asteroid impact, measured 9 km in diameter and caused extreme global cooling and drought. This led to a mass extinction, which not only claimed the lives of the dinosaurs, but also wiped out about 75% of all land and sea animals on Earth.
However, had this asteroid impacted somewhere else on the planet, things could have turned out very differently. According to a new study produced by a team of Japanese researchers, the destruction caused by this asteroid was due in large part to where it impacted. Had the Chicxulub asteroid landed somewhere else on the planet, they argue, the fallout would not have been nearly as severe.
The study, which recently appeared in the journal Scientific Reports, is titled “Site of asteroid impact changed the history of life on Earth: the low probability of mass extinction“, and was conducted by and considered how geological conditions in the Yucatan region were intrinsic to mass extinction that happened 66 million years ago.
Dr. Kaiho and Dr. Oshima began by considering recent studies that have shown how the Chicxulub impact heated the hydrocarbon and sulfur content of rocks in the region. This is what led to the formation of stratospheric soot and sulfate aerosols which caused the extreme global cooling and drought that followed. As they state in their study, it was this (not the impact and the detritus it threw up alone) that ensured the mass extinction that followed:
“Blocking of sunlight by dust and sulfate aerosols ejected from the rocks at the site of the impact (impact target rocks) was proposed as a mechanism to explain how the physical processes of the impact drove the extinction; these effects are short-lived and therefore could not have driven the extinction. However, small fractions of stratospheric sulfate (SO4) aerosols were also produced, which may have contributed to the cooling of the Earth’s surface.“
Another issue they considered was the source of the soot aerosols, which previous research has indicated were quite prevalent in the stratosphere during the Cretaceous/Paleogene (K–Pg) boundary (ca. 65 million years ago). This soot is believed to coincide with the asteroid impact since microfossil and fossil pollen studies of this period also indicate the presence of iridium, which has been traced to the Chicxulub asteroid.
Previously, this soot was believed to be the result of wildfires that raged in the Yucatan as a result of the asteroid impact. However, Kaiho and Oshima determined that these fires could not have resulted in stratospheric soot; instead positing that they could only be produced by the burning and ejecting of hyrdocarbon material from rocks in the impact target area.
The presence of these hydrocarbons in the rocks indicate the presence of both oil and coal, but also plenty of carbonate minerals. Here too, the geology of the Yucatan was key, since the larger geological formation known as the Yucatan Platform is known to be composed of carbonate and soluble rocks – particularly limestone, dolomite and evaporites.
To test just how important the local geology was to the mass extinction that followed, Kaiho and Oshima conducted a computer simulation that took into account where the asteroid struck and how much aerosols and soot would be produced by an impact. Ultimately, they found that the resulting ejecta would have been sufficient to trigger global cooling and drought; and hence, an Extinction Level Event (ELE).
This sulfur and carbon-rich geology, however, is not something the Yucatan Peninsula shares with most regions on the planet. As they state in their study:
“Here we show that the probability of significant global cooling, mass extinction, and the subsequent appearance of mammals was quite low after an asteroid impact on the Earth’s surface. This significant event could have occurred if the asteroid hit the hydrocarbon-rich areas occupying approximately 13% of the Earth’s surface. The site of asteroid impact, therefore, changed the history of life on Earth.”
Basically, Kaiho and Oshima determined that 87% of Earth would not have been able to produce enough sulfate aerosols and soot to trigger a mass extinction. So if the Chicxulub asteroid struck just about anywhere else on the planet, the dinosaurs and most of the world’s animals would have likely survived, and the resulting macroevolution of mammals probably would not have taken place.
In short, modern hominids may very well owe their existence to the fact that the Chicxulub asteroid landed where it did. Granted, the majority of life in the Cretaceous/Paleogene (K–Pg) was wiped out as a result, but ancient mammals and their progeny appear to have lucked out. The study is therefore immensely significant in terms of our understanding of how asteroid impacts affect climatological and biological evolution.
It is also significant when it comes to anticipating future impacts and how they might affect our planet. Whereas a large impact in a sulfur and carbon-rich geological region could lead to another mass extinction, an impact anywhere else could very well be containable. Still, this should not prevent us from developing appropriate countermeasures to ensure that large impacts don’t happen at all!
Further Reading: Science Reports
Up early Sunday morning? Or perhaps, as we often do, you’re “pulling an all-nighter,” out observing until the break of dawn. Well, the clockwork celestial mechanics of the Universe has a treat in store on the morning of October 15th, as the waning crescent Moon occults (passes in front of) the bright star Regulus (Alpha Leonis, the “Little King” or “Heart of the Lion”) for the contiguous United States, Mexico and southern Canada.
You might call this one the “Great American Occultation,” as it takes a similar track to a certain total solar eclipse and another occultation of the bright star Aldebaran earlier this year. The Moon is a 20% illuminated waning crescent during Sunday’s occultation, about the best phase for such an event, as you’ll also get a nice contrasting Earthshine or Ashen light on dark nighttime limb of the Moon. That’s sunlight from the waxing gibbous Earth, illuminating the (cue Pink Floyd) Dark Side of the Moon.
Early morning occultations always see the target star or planet ingress (passing behind) the oncoming bright limb of the waning Moon, then egress (reappearing) from behind its dark limb. During waxing evening occultations, the reverse is true, as the dark limb of the Moon leads the way. The Moon will be 53 degrees west of the Sun during the event, and folks in the western U.S. will see the occultation lower to the eastern horizon under dark skies, while observers from Florida to the Great Lakes will see the event transpire under twilight skies and observers in the U.S. northeast will see the occultation finish up after sunrise. Shining at magnitude +1.4, you’ll be able to see the disappearance and reappearance of Regulus with the unaided eye, though events on the dark limb are always more dramatic. And you may just be able to spy Regulus in the daytime post sunrise near the Moon after the occultation, using binoculars or a telescope.
Observers along a line running from Oregon through Lake of the Woods, above the Great Lakes and north of New Brunswick are also in for a treat as you just might be able to catch a rare grazing occultation of Regulus, (see the video below) as the star’s light shines down through those lunar valleys and gets blocked by mountain peaks along the limb of the Moon. Such an event can be quite dramatic to watch, as the star light winks in and out during the very last second of its 79 light year journey.
A look at the occultation circumstances for selected locations tells the story. The International Occultation Timing Association has a full list for locales across North America.
|Ingress||Egress||Moon Alt start/end|
|Boise, Idaho||9:48 UT||10:03 UT||3 deg / 6 deg|
|Tuscon, Arizona||(before Moonrise)||10:14 UT||NA / 10 deg|
|Mexico City, Mexico||9:19 UT||10:06 UT||6 deg / 17 deg|
|Tampa, Florida||9:24 UT||10:32 UT||23 deg / 39 deg|
|St. Louis, Missouri||9:29 UT||10:26 UT||18 deg / 29 deg|
|Boston, Massachusetts||9:50 UT||10:44 UT||36 deg / 45 deg|
|Toronto, Canada||9:47 UT||10:32 UT||29 / 37 deg|
The Moon is in the midst of a cycle of occultations of Regulus running from December 18th, 2016 to the final one for the cycle on April 24th, 2018. This is number 12 in a series of 19 events, and the best pre-dawn occultation of Regulus for the United States in the current cycle.
The Moon can occult four bright +1st magnitude stars during the current epoch: Regulus, Antares, Spica and Aldebaran. And though Regulus lies closest to the ecliptic plane, it actually gets occulted the least of any 1st magnitude star in the 21st century, with only 220 events. The Moon actually also occulted the bright star Pollux up until almost two millennia ago, and will resume doing so again in the future.
Occultations are easy to observe, and one of the few times (including eclipses) were you can see the motion of the Moon, in real time. The Moon moves its own diameter (30′ or half a degree) per hour, and the reemergence of the bright star will be an abrupt “lights back on” for Regulus. Does it seem to linger a bit between the horns of the crescent Moon? This often reported optical illusion is called the Coleridge Effect, from a line from Samuel Coleridge’s (not Iron Maiden’s) Rime of the Ancient Mariner:
While clome above the Eastern bar
The horned Moon, with one bright star
Almost atween the tips.
Happen to see Regulus “a clome ‘atween the tips?” We also like to refer to this as the ‘Protor and Gamble effect’ due to the company’s traditional star-filled logo.
Occultations also adorn the flags of many Middle Eastern countries. The star and crescent of Islam traces back to antiquity, but was said to have been adapted for the Turkish flag after Sultan Alp Arslan witnessed a close pairing shortly after the Battle of Manzikert on August 26th, 1071 AD. Though Venus is usually stated as the legendary “star,” Regulus was in fact, just a few degrees away from the Moon on the very same morning… perhaps adding some credence to a major legend vexing vexillology?
Of course, we may never truly know just what Sultan Arsulan saw. A more recent occultation tale was featured in the November 2017 issue of Sky and Telescope, positing the an occultation of Aldebaran by the Moon on March 7th, 1974 was the source of William Wilkins’ alleged “Volcano on the Moon…” the timing is certainly right, though one wonders how a skilled observer like Wilkins could be fooled by a prominent star (wistful thinking, maybe?)
Recording an occultation is as easy as aiming a video camera at the Moon through a telescope and letting it run. Start early, and make sure you’ve got the contrast between the bright limb of the Moon and the star adjusted, so both appear in the frame. We like to have WWV radio running in the background for an accurate time hack on the video.
Regulus also has a suspected (though never seen) white dwarf companion. Such a star should shine at +12th magnitude or so… and just might make a very brief appearance on the dark limb of the Moon during egress. One total unknown is its position angle, which is a big wild card, but you just never know… its worth examining that video afterwards, especially if you’re shooting at a high frame rate.
…and speaking of occultations, we’re in the midst of combing through near double occultations of bright stars and planets out to 3000 A.D… hey, it’s what we do for fun. Anyhow, we’re tweeting these out as @Astroguyz as we find ’em, one per day. As a teaser, I give you this grazing occultation of Venus and Regulus over Siberia coming right up in 2025:
If nothing else, the cosmic grin of a planet, star and crescent Moon does hint at the Universe’s strange sense of humor.
Is there life out there in the Universe? That is a question that has plagued humanity long before we knew just how vast the Universe was – i.e. before the advent of modern astronomy. Within the 20th century – thanks to the development of modern telescopes, radio astronomy, and space observatories – multiple efforts have been made in the hopes of finding extra-terrestrial intelligence (ETI).
And yet, humanity is still only aware of one intelligent civilization in the Universe – our own. And until we actually discover an alien civilization, the best we can do is conjecture about the likelihood of their existence. That’s where the famous Drake Equation – named after astronomer Dr. Frank Drake – comes into play. Developed in the 1960s, this equation estimates the number of possible civilizations out there based on a number of factors.
During the 1950s, the concept of using radio astronomy to search for signals that were extra-terrestrial in origin was becoming widely-accepted within the scientific community. The idea of listening for extra-terrestrial radio communications had been suggested as far back as the late 19th century (by Nikolai Tesla), but these efforts were concerned with looking for signs of life on Mars.
Then, in September of 1959, Giuseppe Cocconi and Philip Morrison (who were both physics professors at Cornell University at the time) published an article in the journal Nature with the title “Searching for Interstellar Communications.” In it, they argued that radio telescopes had become sensitive enough that they could pick up transmissions being broadcast from other star systems.
Specifically, they argued that these messages might be transmitted at a wavelength of 21 cm (1420.4 MHz), the same wavelength of radio emissions by neutral hydrogen. As the most common element in the universe, they argued that extra-terrestrial civilizations would see this as a logical frequency at which to make radio broadcasts that could be picked up by other civilizations.
Seven months later, Frank Drake made the first systematic SETI survey at the National Radio Astronomy Observatory in Green Bank, West Virginia. Known as Project Ozma, this survey relied on the observatory’s 25-meter dish to monitor Epsilon Eridani and Tau Ceti – two nearby Sun-like stars – at frequencies close to 21 cm for six hours a day, between April and July of 1960.
Though unsuccessful, the survey piqued the interest of the scientific and SETI communities. It was followed shortly thereafter by a meeting at the Green Bank facility in 1961, where the subjects of SETI and searching for radio signals of extra-terrestrial origin were discussed. In preparation for this meeting, Drake prepared the equation that would come to bear his name. As he said of the equation’s creation:
“As I planned the meeting, I realized a few day[s] ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it’s going to be to detect extraterrestrial life. And looking at them it became pretty evident that if you multiplied all these together, you got a number, N, which is the number of detectable civilizations in our galaxy. This was aimed at the radio search, and not to search for primordial or primitive life forms.”
The meeting, which included such luminaries as Carl Sagan, was commemorated with a commemorative plaque that is still in the hall of the Green Bank Observatory today.
The formula for the Drake Equation is as follows:
N = R* x fp x ne x fl x fi x fc x L
Whereas N is the number of civilizations in our galaxy that we might able to communicate with, R* is the average rate of star formation in our galaxy, fp is the fraction of those stars which have planets, ne is the number of planets that can actually support life, fl is the number of planets that will develop life, fi is the number of planets that will develop intelligent life, fc is the number civilizations that would develop transmission technologies, and L is the length of time that these civilizations would have to transmit their signals into space.
Limits and Criticism:
Naturally, the Drake Equation has been subject to some criticism over the years, largely because a lot of the values it contains are assumed. Granted, some of the values it takes into account are easy enough to calculate, like the rate of star formation in the Milky Way. There are an estimated 200 – 400 billion stars within our Milky Way, and modern estimates say that there between 1.65 ± 0.19 and 3 new star form every year.
Assuming that our galaxy represents the average, and given that that there are as many as 2 trillion galaxies in the observable Universe (current estimates based on Hubble data), that means that there are as many as 1.5 to 6 trillion new stars being added to the Universe with every passing year! However, some of the other values are subject to a great deal of guess work.
For example, estimates on how many stars will have a system of planets has changed over time. Currently, it is estimated that the Milky Way contains 100 billion planets, which works out to about 50% of its stars having a planet of their own. Furthermore, those stars that have multiple planets will likely have one or two that lies within their habitable zone (aka. “Goldilocks Zone”) – where liquid water can exist on their surfaces.
Now let’s assume that 100% of planets located within a habitable zone will be able develop life in some form, that at least 1% of those life-supporting planets will be able to give rise to intelligent species, that 1% of these will be able to communicate, and that they will able to do so for a period of about 10,000 years. If we run those numbers through the Drake Equation, we end up with a value of 10.
In other words, there are possibly 10 civilizations in the Milky Way at any time capable of sending out signals that we could detect. But of course, the values used for four parameters there – fl, fi, fc and L – were entirely assumed. Without any real data to go by, there’s no real way to know how many alien civilizations could really be out there. There could just be 1 in the entire Universe (us), or millions in every galaxy!
The Fermi Paradox:
Beyond the issue of assumed values, the most pointed criticism of the Drake Equation tend to emphasize the argument put forth by physicist Enrico Fermi, known as the Fermi Paradox. This argument arose in 1950 as a result of conversation between Fermi and some colleagues while he was working at the Los Alamos National Laboratory. When the subject of UFOs and ETI came up, Fermi famously asked, “Where is everybody?”
This simple question summarized the conflict that existed between arguments that emphasized scale and the high probability of life emerging in the Universe with the complete lack of evidence that any such life exists. While Fermi was not the first scientists to ask the question, his name came to be associated with it due to his many writings on the subject.
In short, the Fermi Paradox states that, given the sheer number of stars in the Universe (many of which are billions of years older than our own), the high-probability that even a small fraction would have planets capable of giving rise to intelligent species, the likelihood that some of them would develop interstellar travel, and the time it would take to travel from one side of our galaxy to other (even allowing for sub-luminous speeds), humanity should have found some evidence of intelligent civilizations by now.
Naturally, this has given rise to many hypotheses as to how advanced civilizations could exist within our Universe but remain undetected. They include the possibility that intelligent life is extremely rare, that humanity is an early arrival to the Universe, that they do not exist (aka. the Hart-Tipler Conjecture), that they are in a state of slumber, or that we are simply looking in the wrong places.
The “Great Filter” Hypothesis:
But perhaps the best known explanation for why no signs of intelligence life have been found yet is the “Great Filter” hypothesis. This states that since that no extraterrestrial civilizations have been so far, despite the vast number of stars, then some step in the process – between life emerging and becomes technologically advanced – must be acting as a filter to reduce the final value.
According to this view, either it is very hard for intelligent life to arise, the lifetime of such civilizations is short, or the time they have to reveal their existence is short. Here too, various explanations have been offered to explain what the form the filter could take, which include Extinction Level Events (ELEs), the inability of life to create a stable environment in time, environmental destruction. and/or technology running amok (some of which we fear might happen to us!)
Alas, the Drake Equation has endured for decades for the very same reason that if often comes under fire. Until such time that humanity can find evidence of intelligent life in the Universe, or has ruled out the possibility based on countless surveys that actually inspect other star systems up close, we won’t be able to answer the question, “Where is everybody?”
As with many other cosmological mysteries, we’ll be forced to guess about what we don’t know based on what we do (or think we do). As astronomers study stars and planets with newer instruments, they might eventually be able to work out just how accurate the Drake Equation really is. And if our recent cosmological and exoplanet-hunting efforts have shown us anything, it is that we are just beginning to scratch the surface of the Universe at large!
In the coming years and decades, our efforts to learn more about extra-solar planets will expand to include research of their atmospheres – which will rely on next-generation instruments like the James Webb Space Telescope and the European Extremely-Large Telescope array. These will go a long way towards refining our estimates on how common potentially habitable worlds are.
In the meantime, all we can do is look, listen, wait and see…
We have written many articles about the Drake Equation for Universe Today. Here’s Inside the Drake Equation: A Chat with Frank Drake, The Odds of Intelligent Life in the Universe, A New Drake Equation? Other Life Not Likely to be Intelligent, A New Drake Equation for Potential of Life, Bayesian Analysis Rains on Exoplanet Life Parade, and Where are all the Aliens? The Fermi Paradox?
There are some great resources out there on the Internet. Check out this Drake Equation calculator.
We have recorded an entire episode of Astronomy Cast about the Drake Equation. Check it out here, Episode 23 – Counting Aliens with the Drake Equation.
If you’ve got really good eyesight and can find a place where the light pollution is non-existent, you might be able to see Uranus without a telescope. It’s only possible with the right conditions, and if you know exactly where to look. And for thousands of years, scholars and astronomers were doing just that. But given that it was just a tiny pinprick of light, they believed Uranus was a star.
It was not until the late 18th century that the first recorded observation that recognized Uranus as being a planet took place. This occurred on March 13th, 1781, when British astronomer Sir William Herschel observed the planet using a telescope of his own creation. From this point onwards, Uranus would be recognized as the seventh planet and the third gas giant of the Solar System.
Observations pre-18th Century:
The first recorded instance of Uranus being spotted in the night sky is believed to date back to Classical Antiquity. During the 2nd century BCE, Hipparchos – the Greek astronomer, mathematician and founder of trigonometry – apparently recorded the planet as a star in his star catalogue (completed in 129 BCE).
This catalog was later incorporated into Ptolemy’s Almagest, which became the definitive source for Islamic astronomers and for scholars in Medieval Europe for over one-thousand years. During the 17th and 18th centuries, multiple recorded sightings were made by astronomers who also catalogued it as being a star.
This included English astronomer John Flamsteed, who in 1690 observed the star on six occasions and catalogued it as a star in the Taurus constellation (34 Tauri). During the mid-18th century, French astronomer Pierre Lemonnier made twelve recorded sightings, and also recorded it as being a star. It was not until March 13th, 1781, when William Herschel observed it from his garden house in Bath, that Uranus’ true nature began to be revealed.
On the evening in question – March 13th, 1781 – William Herschel was surveying the sky with his telescope, looking for binary stars. His first report on the object was recorded on April 26th, 1781. Initially, he described it as being a “Nebulous star or perhaps a comet”, but later settled on it being a comet since it appeared to have changed its position in the sky.
When he presented his discovery to the Royal Society, he maintained this theory, but also likened it to a planet. As was recorded in the Journal of the Royal Society and Royal Astronomical Society on the occasion of his presentation:
“The power I had on when I first saw the comet was 227. From experience I know that the diameters of the fixed stars are not proportionally magnified with higher powers, as planets are; therefore I now put the powers at 460 and 932, and found that the diameter of the comet increased in proportion to the power, as it ought to be, on the supposition of its not being a fixed star, while the diameters of the stars to which I compared it were not increased in the same ratio. Moreover, the comet being magnified much beyond what its light would admit of, appeared hazy and ill-defined with these great powers, while the stars preserved that lustre and distinctness which from many thousand observations I knew they would retain. The sequel has shown that my surmises were well-founded, this proving to be the Comet we have lately observed.”
While Herschel would continue to maintain that what he observed was a comet, his “discovery” stimulated debate in the astronomical community about what Uranus was. In time, astronomers like Johann Elert Bode would conclude that it was a planet, based on its nearly-circular orbit. By 1783, Herschel himself acknowledged that it was a planet to the Royal Society.
As he lived in England, Herschel originally wanted to name Uranus after his patron, King George III. Specifically, he wanted to call it Georgium Sidus (Latin for “George’s Star”), or the Georgian Planet. Although this was a popular name in Britain, the international astronomy community didn’t think much of it, and wanted to follow the historical precedent of naming the planets after ancient Greek and Roman gods.
Consistent with this, Bode proposed the name Uranus in a 1782 treatise. The Latin form of Ouranos, Uranus was the grandfather of Zeus (Jupiter in the Roman pantheon), the father of Cronos (Saturn), and the king of the Titans in Greek mythology. As it was discovered beyond the orbits of Jupiter and Saturn, the name seemed highly appropriate.
In the following century, Neptune would be discovered, the last of the eight official planets that are currently recognized by the IAU. And by the 20th century, astronomers would discovery Pluto and other minor planets within the Kuiper Belt. The process of discovery has been ongoing, and will likely continue for some time to come.
We have written many articles about planetary discovery here at Universe Today. Here’s Who Discovered Mercury?, Who Discovered Venus?, Who Discovered Earth?, Who Discovered Mars?, Who Discovered Jupiter?, Who Discovered Saturn?, Who Discovered Neptune?, and Who Discovered Pluto?
We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.
Been missing the evening planets? Currently, Saturn and Venus rule the dawn, and Mars is sinking into the dusk as it recedes towards the far side of the Sun. The situation has been changing for one planet however, as Jupiter reaches opposition this week.
Jupiter in 2017
Currently in the constellation Virgo near the September equinoctial point where the celestial equator meets the ecliptic in 2017, Jupiter rules the evening skies. Orbiting the Sun once every 11.9 years, Jupiter moves roughly one zodiacal constellation eastward per year, as oppositions for Jupiter occur about once every 399 days.
As the name implies, “opposition” is simply the point at which a planet seems to rise “opposite” to the setting Sun.
At opposition 2017 on Friday, April 7th, Jupiter shines at magnitude -2.5 and is 666.5 million kilometers distant. Jupiter just passed aphelion on February 16th, 2017 at 5.46 AU 846 million kilometers from the Sun, making this and recent oppositions slightly less favorable. An April opposition for Jupiter also means it’ll now start to occur in the southern hemisphere for this and the next several years. Jupiter crosses the celestial equator northward again in 2022.
Can you see Ganymede with the naked eye? Shining at magnitude +4.6, the moon lies just on the edge of naked eye visibility from a dark sky site… the problem is, the moon never strays more than 5′ from the dazzling limb of Jupiter. Here’s a fun and easy experiment: attempt to spot Ganymede through this month’s opposition season, using nothing more than a pair of MK-1 eyeballs. Then at the end of the month, check an ephemeris for greatest elongations of the moon. Any matches?
With binoculars, the first thing you’ll notice is the four bright Galilean moons of Io, Europa, Ganymede and Callisto. At about 10x magnification or so, Jupiter will begin to resolve as a disk. With binoculars, you get a very similar view of Jupiter as Galileo had with his primitive spy glass.
At the telescope eyepiece at low power you can see the main cloud bands of Jove, the northern and southern equatorial belts. Shadow transits and eclipses of the Jovian moons are also fun to watch, and frequent for the innermost two moons Io and Europa. Orbiting Jupiter once every seven days, transits of Ganymede are less frequent, and outermost Callisto is the only moon that can “miss” Jupiter on occasion, as it does this year until transits resume in 2020.
Jupiter’s one of the best planets for imaging: unlike Venus or bashful Mars, things are actually happening on the cloudtops of Jove. You can see smaller storms come and go as the Great Red Spot make its circuit once every 10 hours. Follow Jupiter from sunset through sunrise, and it will rotate just about all the way around once. Strange to think, we’ve been using modified webcams to image Jupiter for over a decade and a half now.
The major moons of Jupiter cast shadows nearly straight back as seen from our vantage point near opposition. After opposition, the shadows of the moons and the planet itself begin to slide to one side and will continue to do so as the planet heads towards quadrature 90 degrees east of the Sun. In 2017, quadrature for Jupiter occurs on July 5th as the planet sits due south for northern hemisphere observers at sunset. Distances to Jupiter vary through opposition, quadrature and solar conjunction, and Danish astronomer Ole Rømer used discrepancies in predictions versus actual observed phenomena of Jupiter’s moons to make the first good estimation of the speed of light in 1676.
Double shadow transits are also interesting to watch, and a season of double events involving Io and Europa begins next month on May 12th.
Jupiter will rule the dusk skies until solar conjunction on October 26th, 2017.
It’s also interesting to note that while the Northern Equatorial Belt has been permanent over the last few centuries of telescopic observation, the Southern Equatorial Belt seems to pull a disappearing act roughly every decade or so. This last occurred in 2010, and we might just be due again over the next few years. The Great Red Spot has also looked a little more pale and salmon over the last few years, and may vanish altogether this century.
Finally, the Full Moon typically sits near a given planet near opposition, as occurs next week on the evening of April 10/11th.
The next occultation of Jupiter by the Moon occurs on October 31st, 2019.
Don’t miss a chance to observe the king of the planets in 2017.
– Here’s a handy JoveMoons for Android and Iphone for planning your next Jovian observing session.
-Be sure to check out our complete guide to oppositions, elongations, occultations and more with our 101 Astronomical Events for 2017, a free e-book from Universe Today.
-Send those images of Jupiter in to Universe Today’s Flickr forum.
Have you seen it yet? An old friend greeted us on an early morning run yesterday as we could easily spy brilliant Venus in the dawn, just three days after inferior conjunction this past Saturday on March 25th.
This was an especially wide pass, as the planet crossed just over eight degrees (that’s 16 Full Moon diameters!) north of the Sun. We once managed to see Venus with the unaided eye on the very day of inferior conjunction back in 1998 from the high northern latitudes of the Chena Flood Channel just outside of Fairbanks, Alaska.
The planet was a slender 59.4” wide, 1% illuminated crescent during this past weekend’s passage, and the wide pass spurred many advanced imagers to hunt for the slim crescent in the daytime sky. Of course, such a feat is challenging near the dazzling daytime Sun. Safely blocking the Sun out of view and being able to precisely point your equipment is key in this endeavor. A deep blue, high contrast sky helps, as well. Still, many Universe Today readers rose to the challenge of chronicling the horns of the slender crescent Venus as they rotated ’round the limb and the nearby world moved once again from being a dusk to dawn object.
The orbit of Venus is tilted 3.4 degrees with respect to the Earth, otherwise, we’d get a transit of the planet like we did on June 5-6th, 2012 once about every 584 days, instead of having to wait again until next century on December 10th, 2117.
The joint NASA/European Space Agency’s SOlar Heliospheric Observatory (SOHO) mission also spied the planet this past weekend as it just grazed the 15 degree wide field of view of its Sun-observing LASCO C3 camera:
Venus kicks off April as a 58” wide, 3% illuminated crescent and ends the month at 37” wide, fattening up to 28% illumination. On closest approach, the planet presents the largest apparent planetary disk possible as seen from the Earth. Can you see the horns? They’re readily readily apparent even in a low power pair of hunting binoculars. The coming week is a great time to try and see a crescent Venus… with the naked eye. Such an observation is notoriously difficult, and right on the edge of possibility for those with keen eyesight.
One problem for seasoned observers is that we know beforehand that (spoiler alert) that the Horns of Venus, like the Moon, always point away from the direction of the Sun.
True Story: a five year old girl at a public star party once asked me “why does that ‘star’ look like a tiny Moon” (!) This was prior to looking at the planet through a telescope. Children generally have sharper eyes than adults, as the lenses of our corneas wear down and yellow from ultraviolet light exposure over the years.
Still, there are tantalizing historical records that suggest that ancient cultures such as the Babylonians knew something of the true crescent nature of Venus in pre-telescopic times as well.
Another fun challenge in the coming months is attempting to see Venus in the daytime. This is surprisingly easy, once you know exactly where to look for it. A nearby crescent Moon is handy, as occurs on April 23rd, May 22nd, and June 20th.
Strangely enough, the Moon is actually darker than dazzling Venus in terms of surface albedo. The ghostly daytime Moon is just larger and easier to spot. Many historical ‘UFO’ sightings such as a ‘dazzling light seen near the daytime Moon’ by the startled residents of Saint-Denis, France on the morning on January 13th, 1589 were, in fact, said brilliant planet.
Venus can appear startlingly bright to even a seasoned observer. We’ve seen the planet rise as a shimmering ember against a deep dark twilight sky from high northern latitudes. Air traffic controllers have tried in vain to ‘hail’ Venus on more than one occasion, and India once nearly traded shots with China along its northern border in 2012, mistaking a bright conjunction of Jupiter and Venus for spy drones.
The third brightest object in the sky behind the Sun and the Moon, Venus is even bright enough to cast a shadow as seen from a dark sky site, something that can be more readily recorded photographically.
Watch our nearest planetary neighbor long enough, and it will nearly repeat the same pattern for a given apparition. This is known as the eight year cycle of Venus, and stems from the fact that 13 Venusian orbits (8x 224.8 days) very nearly equals eight Earth years.
Follow Venus through the dawn in 2017, and it will eventually form a right triangle with the Earth and the Sun on June 3rd, reaching what is known as greatest elongation. This can vary from 47.2 to 45.4 degrees from the Sun, and this year reaches 45.9 degrees elongation in June. The planet then reaches half phase known as dichotomy around this date, though observed versus theoretical dichotomy can vary by three days. The cause of this phenomenon is thought to be the refraction of light in Venus’ dense atmosphere, coupled with observer bias due to the brilliance of Venus itself. When do you see it?
Also, keep an eye out for the ghostly glow on the night-side of Venus, known as Ashen Light. Long thought to be another trick of the eye, there’s good evidence to suggest that this long reported effect actually has a physical basis, though Venus has no large reflecting moon nearby… how could this be? The leading candidate is now thought to be air-glow radiating from the cooling nighttime side of the planet.
Cloud enshrouded Venus held on to its secrets, right up until the Space Age less than a century ago… some observers theorized that the nighttime glow on Venus was due to aurorae, volcanoes or even light pollution from Venusian cities (!). This also fueled spurious sightings of the alleged Venusian moon Neith right up through the 19th century.
Venus should also put in a showing 34 degrees west of the Sun shining at magnitude -4 during the August 21st, 2017 total solar eclipse. Follow that planet, as it makes a complex meet up with Mars, Mercury, and the Moon in late September of this year.
More to come!
-Read about planets, occultations, comets and more for the year in our 101 Astronomical Events for 2017, out as a free e-book from Universe Today.
In the southern hemisphere this weekend in the ‘Land of Oz?’ Are you missing out on the passage of Comet 45/P Honda-Mrkos-Pajdušáková, and the penumbral lunar eclipse? Fear not, there’s an astronomical event designed just for you, as the Moon occults (passes in front of) the bright star Regulus on the evening of Saturday, January 11th.
The entire event is custom made for the continent of Australia and New Zealand, occurring under dark skies. Now for the bad news: the waning gibbous Moon will be less than 14 hours past Full during the event, meaning that the ingress (disappearance) of Regulus will occur along its bright leading limb and egress (reappearance) will occur on the dark limb. We prefer occultations during waxing phase, as the star winks out on the dark limb and seems to slowly fade back in on the bright limb.
The International Occultation Timing Association has a complete list of precise ingress/egress times for cities located across the continent. An especially interesting region to catch the event lies along the northern graze line across the sparsely populated Cape York peninsula, just north of Cairns.
The Moon occults Aldebaran and then Regulus six days later during every lunation in 2017. This is occultation number three in a cycle of 19 running from December 18, 2016 to April 24, 2018. The Moon occults Regulus 214 times in the 21st century, and Regulus is currently the closest bright star to the ecliptic plane, just 27′ away.
We’ve also got a very special event just under 14 hours prior, as a penumbral lunar eclipse occurs, visible on all continents… except Australia. Mid-eclipse occurs at 00:45 Universal Time (UT, Saturday morning on February 11th), or 7:45 PM Eastern Standard Time (EST) on the evening of Friday, February 10th, when observers may note a dusky shading on the northern limb of the Moon as the Moon just misses passing through the dark edge of the Earth’s inner umbral shadow. Regulus will sit less than seven degrees off of the lunar limb at mid-eclipse Friday night.
How often does an eclipsed Moon occult a bright star? Well, stick around until over four centuries from now on February 22nd, 2445, and observers based around the Indian Ocean region can watch just such an event, as the eclipsed Moon also occults Regulus. Let’s see, I should have my consciousness downloaded into my second android body by then…
We’ll be streaming the Friday night eclipse live from Astroguyz HQ here in Spring Hill, Florida starting at 7:30 PM EST/00:30 UT, wifi-willing. Astronomer Gianluca Masi of the Virtual Telescope Project will also carry the eclipse live starting at 22:15 UT on the night of Friday, February 10th.
This eclipse also marks the start of eclipse season one of two, which climaxes with an annular eclipse crossing southern Africa and South America on February 26th. The second and final eclipse season of 2017 starts with a partial lunar eclipse on August 7th, which sets us up for the Great American Eclipse crossing the United States from coast to coast on August 21st, 2017.
A lunar occultation of Regulus also provides a shot at a unique scientific opportunity. Spectroscopic measurements suggest that the primary main sequence star possesses a small white dwarf companion, a partner which has never been directly observed. This unseen white dwarf may – depending on the unknown orientation of its orbit – make a brief appearance during ingress or egress for a fleeting split second, when the dark limb of the Moon has covered dazzling Regulus. High speed video might just nab a double step occlusion, as the white dwarf companion is probably about 10,000 times fainter than Regulus at magnitude +11 at the very brightest. Regulus is located 79 light years distant.
Our best results for capturing an occultation of a star or planet by the Moon have always been with a video camera aimed straight through our 8” Schmidt-Cassegrain telescope. The trick is always to keep the star visible in the frame near the brilliant Full Moon. Cropping the Moon out of the field as much as possible can help somewhat. Set up early, to work the bugs out of focusing, alignment, etc. We also run WWV radio in the background for an audible time hack on the video.
The best occultation of Regulus by the Moon for North America in 2017 occurs on October 15th, when the Moon is at waning crescent phase. Unfortunately, the occultation of Regulus by asteroid 163 Erigone back in 2014 was clouded out, though the planet Venus occults the star on October 1st, 2044. Let’s see, by then I’ll be…
Comets and eclipses and occultations, oh my. It’s a busy weekend for observational astronomy, for sure. Consider it an early Valentine’s Day weekend gift from the Universe.
Webcasting the eclipse or the occultation this weekend? Let us know, and send those images of either event to Universe Today’s Flickr forum.
Read about eclipses, occultations and more tales of astronomy in our yearly guide 101 Astronomical Events For 2017, free from Universe Today.