The Story of the Apollo Guidance Computer, Part 3

During the development of the Apollo Guidance Computer (AGC) by the MIT Instrumentation Laboratory (see Part 1 and Part 2 for the complete backstory), an inauspicious event occurred sometime during 1965-1966, while the Gemini missions were going on.

The Gemini program helped NASA get ready for the Apollo Moon landings missions by testing out rendezvous and other critical techniques and technologies. Ten crews flew missions in Earth orbit on the two-person Gemini spacecraft.

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The Story of the Apollo Guidance Computer, Part 2

In the late 1950’s, before NASA had any intentions of going to the Moon – or needing a computer to get there — the MIT Instrumentation Laboratory had designed and built a small prototype probe they hoped would one day fly to Mars (read the background in part 1 of this story here).  This little probe used a small, rudimentary general-purpose computer for navigation, based on the inertial systems for ballistic missiles, submarines, and aircraft the Lab had designed and built for the military since World War II.

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The Story of the Apollo Guidance Computer, Part 1

Dick Battin stood on his driveway in the New England frosty pre-dawn back in October 1957, straining his eyes to see Sputnik fly overhead. It was amazing. Watching that little point of light scoot silently across the sky made Battin’s heart pound. A human-made hunk of metal was actually orbiting Earth!

Walking back to his house, Battin’s mind raced. Oh, how he wished he’d never left the MIT Instrumentation Laboratory a year and a half ago. He’d regretted it since the day he decided to move on to what he thought were greener pastures. But now, his regret became a steadfast resolve to somehow get back to the Lab again, because he knew – he was absolutely certain without a doubt – that Doc Draper would be getting his hand in this new venture of space exploration. And Battin wanted in, too.

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Researchers May Have Found the Missing Piece of Evidence that Explains the Origins of Life

Structure of DNA

The question of how life first emerged here on Earth is a mystery that continues to elude scientists. Despite everything that scientists have learned from the fossil record and geological history, it is still not known how organic life emerged from inorganic elements (a process known as abiogenesis) billions of years ago.

One of the more daunting aspects of the mystery has to do with peptides and enzymes, which fall into something of a “chicken and egg” situation. Addressing this, a team of researchers from the University College London (UCL) recently conducted a study that effectively demonstrated that peptides could have formed in conditions analogus to primordial Earth.

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The First-Ever Film of a Total Solar Eclipse – in 1900 – was Just Discovered and Restored

The first film of a total solar eclipse has been restored by specialists at the British Film Institute (BFI) and made available for viewing. The film was taken in North Caroline in 1900 by Nevil Maskelyne. Maskelyne was a British man who was a magician turned film-maker. He took the film as part of a Royal Astronomical Society (RAS) expedition.

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Are We Witnessing the Start of Solar Cycle 25?

Solar sunspot

Solar sunspot
A precursor to the start of Solar Cycle 25? The Sun in hydrogen alpha from August 25th, 2018, showing enigmatic sunspot AR 2720. Image credit and copyright: Damien Weatherly.

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.

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Asteroids Smack Jupiter More Often Than Astronomers Thought

Jupiter Impact

Jupiter Impact
Pow: The July 1994 impact of Comet Shoemaker-Levy 9 on Jupiter, captured by the Hubble Space Telescope. Credit: R. Evans/J. Trauger/H. Hammel/HST Comet Science Team/NASA.

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.”

Small asteroid impacts over the span of the Earth over a 20 year period. NASA/Planetary Science.

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.

An impact scar (top center on the disk) on Jupiter, captured on July 19th, 2009. Image credit: Anthony Wesley.

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.

Finding Jupiter: looking eastward tonight at around 11PM local. Credit Stellarium.

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.

Hale-Bopp’s close inbound passage near Jupiter in 1996. Credit: NASA/JPL-Horizons.

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!

Antarctica has a Huge Mantle Plume Beneath it, Which Might Explain Why its Ice Sheet is so Unstable

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.

Glaciers seen during NASA’s Operation IceBridge research flight to West Antarctica on Oct. 29, 2014. Credit: NASA/Michael Studinger

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.

A view of mountains and glaciers in Antarctica’s Marie Byrd Land seen during the Nov. 2nd, 2014, IceBridge survey flight. Credit: NASA / Michael Studinger

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.

Temperature changes in the Antarctic ice sheet over the last 50 years, measured in degrees Celsius. Credit: NASA/GSFC Scientific Visualization Studio

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.

Further Reading: NASA, Journal of Geophysical Research

Dinosaur Killing Asteroid hit Earth in Exactly the Wrong Spot

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 Reportsis titled “Site of asteroid impact changed the history of life on Earth: the low probability of mass extinctionand was conducted by Kunio Kaiho and Naga Oshima of Tohoku University and the Meteorological Research Institute, respectively. For the sake of their study, the pair considered how geological conditions in the Yucatan region were intrinsic to mass extinction that happened 66 million years ago.

Satellite views of the Chicxulub impact site in the Yucutan Peninsula, southern Mexico. Image credit: NASA/JPL

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.

When an asteroid struck the Yucatan region about 66 million years ago, it wiped out the dinosaurs, and most of life on Earth. If it had hit elsewhere, the dinosaurs might well have survived. Credit: NASA/Don Davis
When an asteroid struck the Yucatan region about 66 million years ago, it wiped out the dinosaurs, and most of life on Earth. If it had hit elsewhere, the dinosaurs might well have survived. Credit: NASA/Don Davis

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.”

Mass extinction only occurred when the asteroid having 9-km diameter hit the orange areas. Credit: Kunio Kaiho

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

Tales of the King: Watch as the Moon Occults Regulus for North America This Weekend

The Moon occults Regulus on July 25th, 2017. The Moon also occulted the star shortly after the August 21st total solar eclipse. Credit and copyright: @Shahgazer (Shahrin Ahmad).

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.

The visibility footprint for Sunday’s occultation. The white solid lines show where the occultation occurs under dark skies, blue marks twilight, and broken lines represent where the event occurs under daytime skies. Credit: Occult 4.2.

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.

Moon versus Regulus shortly after Sunday’s occultation as seen from Spring Hill, Florida. Stellarium.

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.

The northern limit graze line path for Sunday’s occultation. Click here for a Google interactive map. Credit: IOTA

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.

US cloud cover percentages, a few hours before the occultation. Credit: NOAA

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?

The Moon and Regulus on the morning of August 26th, 1071 AD. Stellarium.

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:

The Moon occults Venus and Regulus in 2025. Stellarium.

If nothing else, the cosmic grin of a planet, star and crescent Moon does hint at the Universe’s strange sense of humor.