On November 19, the longest partial lunar eclipse in the last 580 years happened, and if you missed it, mark your calendars for the next astronomical event.
Last Friday, the Moon entered Earth’s shadow for nearly three and a half hours, and while the timeframe for viewing was small, many people managed to snap some awesome images of the event. If you were unlucky and didn’t get to see the partial lunar eclipse in person, you will be pleased to know that another one is coming up, and this time it’s a total lunar eclipse not a partial. For those that don’t know, a lunar eclipse happens when the Earth passes between the Sun and the Moon. The Moon then enters Earth’s shadow for a period of time.
So, why does the Moon appear red during a lunar eclipse? The Earth is blocking the majority of the Sun rays as it’s in between the Moon and the Sun. However, some of the rays from the Sun go around the Earth and pass through Earth’s atmosphere, which only lets long wavelengths of light such as red pass through. According to TimeandDate.com, the next lunar eclipse will happen between May 15 and 16, 2022. TimeandDate state that the total lunar eclipse will be visible for people in North and South America, Europe, Africa, and parts of Asia.
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Sechelt Skies: Sun, Earth and moon align for awesome tides – Coast Reporter
There will be some interesting lunar action this December as Venus makes a close approach.
The new moon will occur very early on Dec. 4 and will pass below Venus, less than three degrees away, then by Saturn and Jupiter successively Dec. 7 through Dec. 9. The close pass by Venus will be neat for anyone with a decent telescope – you’ll be able to see the moon as a thin crescent and a remarkably similar-looking thin crescent of Venus about one fiftieth the size of the moon.
By about Christmas Day, Venus will appear lower in the southwest just after sunset as it heads west to pass between us and the sun (inferior conjunction) on Jan. 8. Mercury will join Venus over the next two weeks as Mercury moves east and out from behind the sun. Their closest approach will be about three degrees on Dec. 28. By Jan. 8, Venus will be only 0.266 astronomical units (the Earth-sun mean distance) from Earth and just more than one minute of arc in apparent diameter – one thirtieth the size of the moon. This is discernible even with a pair of 7 x 30 binoculars as a reasonably large but very thin crescent. The convenient part is that, since Venus’ orbit is tipped to our own, it will pass about five degrees north of the sun and will be visible for a week or two both in the evening in the southwest and the morning in the southeast.
Something we’re all looking forward to: the winter solstice occurs at 0859 on Dec. 21 and the days begin to get longer.
One other neat thing about this month is that the new moon and lunar perigee – closest approach to Earth – occur only three hours apart on Dec. 4. As well, Earth’s perihelion – closest approach to the sun – occurs on Jan. 3. This means that on Dec. 4, the moon is just about as close as it gets to the Earth and the Earth is nearly as close as it gets to the sun. Since all three are in a nearly straight line all of the tidal effects add up. When two objects orbit each other gravitationally, they each have a gravitational field that decreases as the square of the distance away from each. That means that each body sees a slightly stronger pull of gravity on the side facing the other body and slightly weaker on the side opposite. Since Earth has liquid oceans, they will bulge slightly toward the moon when it’s overhead; on the side farthest away, they see a slightly lower pull from the moon so they bulge away from the moon.
As the TV advertisers say: “But, wait, there’s more!” The oceans also respond to the sun’s gravitational field in the same way. As far as I can figure out (and I’m hitting the limits on my long, long ago math degree), the tidal forces vary as the mass of the attracting body divided by the cube of its distance. If you look up all the mean values for the sun and the moon, you get values of 594 for the sun and 1,288 for the moon. Units are metric tons per cubic kilometre, whatever that actually means. Anyway, the ratio means that the sun exerts a tidal force on the Earth of about 46 per cent of that of the moon. For the Dec. 4 new moon, however, the tidal forces rise to 621 and 1,618 for sun and moon, respectively; this is a total of about 19 per cent greater tidal forces than average. The remaining complication is that the tidal bulges are at their peaks in the plane of Earth’s orbit; in our winter they’re near the Tropic of Capricorn sunward and the Tropic of Cancer away from the sun. That means we’ll see a big variation from day (lower) to night (higher). We seem to see the greatest range about two to three days after the new and full moon for reasons I don’t understand. But, I’d say we can expect some awesome tides the night of Dec. 6. We’ll see pretty much the same in early January too; a little more from the sun and a bit less from the moon.
The remaining complication is that the shape of our coastlines and ocean depths can hugely affect tides. Best examples: Bay of Fundy and Cook Inlet in Alaska (leads to Anchorage). In both cases, the shape and depths of each leads to a resonance period just about the same as the lunar tidal period so the water sloshes in and out like a kid on a swing in time with the moon’s pull. The whole subject is the sort of thing that highly nerdy careers are made of.
Bruce Fryer’s presentation on this and other subjects can be watched on YouTube by entering Sunshine Coast Astronomy in the search line. I found it excellent and will recommend any of the stuff on the channel. The next online Sunshine Coast Astronomy Club meeting is Dec. 10 at 7 p.m. Signup information will be available at sunshinecoastastronomy.wordpress.com.
Could we really deflect an asteroid heading for Earth? An expert explains NASA's latest DART mission – Phys.Org
A NASA spacecraft the size of a golf cart has been directed to smash into an asteroid, with the intention of knocking it slightly off course. The test aims to demonstrate our technological readiness in case an actual asteroid threat is detected in the future.
The Double Asteroid Redirection Test (DART) lifted off aboard a SpaceX rocket from California on November 23, and will arrive at the target asteroid system in September, next year.
The mission will travel to the asteroid Didymos, a member of the Amor group of asteroids. Every 12 hours Didymos is orbited by a mini-moon, or “moonlet”, Dimorphos. This smaller half of the pair will be DART’s target.
Are we facing an extinction threat from asteroids?
We’ve all seen disaster movies in which an asteroid hits Earth, creating an extinction event similar to the one that killed off the dinosaurs millions of years ago. Could that happen now?
Well, Earth is actually bombarded frequently by small asteroids, ranging from 1-20 metres in diameter. Almost all asteroids of this size disintegrate in the atmosphere and are usually harmless.
There is an inverse relationship between the size of these object and the frequency of impact events. This means we get hit much more frequently by small objects than larger ones—simply because there are many more smaller objects in space.
Asteroids with a 1km diameter strike Earth every 500,000 years, on average. The most “recent” impact of this size is thought to have formed the Tenoumer impact crater in Mauritania, 20,000 years ago. Asteroids with an approximate 5km diameter impact Earth about once every 20 million years.
The 2013 Chelyabinsk meteoroid, which damaged buildings in six Russian cities and injured around 1,500 people, was estimated to be about 20m in diameter.
Assessing the risk
NASA’s DART mission has been sparked by the threat and fear of a major asteroid hitting Earth in the future.
The Torino scale is a method for categorising the impact hazard associated with a near-Earth object (NEO). It uses a scale from 0 to 10, wherein 0 means there is negligibly small chance of collision, and 10 means imminent collision, with the impacting object being large enough to precipitate a global disaster.
The Chicxulub impact (which is attributed to the extinction of non-avian dinosaurs) was a Torino scale 10. The impacts that created the Barringer Crater, and the 1908 Tunguska event, both correspond to Torino Scale 8.
With the increase of online news and individuals’ ability to film events, asteroid “near-misses” tend to generate fear in the public. Currently, NASA is keeping a close eye on asteroid Bennu, which is the object with the largest “cumulative hazard rating” right now. (You can keep up to date too).
With a 500m diameter, Bennu is capable of creating a 5km crater on Earth. However, NASA has also said there is a 99.943% chance the asteroid will miss us.
Brace for impact
At one point in their orbit around the Sun, Didymos and Dimorphos come within about 5.9 million km of Earth. This is still further away than our Moon, but it’s very close in astronomical terms, so this is when DART will hit Dimorphos.
DART will spend about ten months travelling towards Didymos and, when it’s close by, will change direction slightly to crash into Dimorphos at a speed of about 6.6km per second.
The larger Didymos is 780m in diameter and thus makes a better target for DART to aim for. Once DART has detected the much smaller Dimorphos, just 160m in diameter, it can make a last-minute course correction to collide with the moonlet.
The mass of Dimorphos is 4.8 million tonnes and the mass of DART at impact will be about 550kg. Travelling at 6.6km/s, DART will be able to transfer a huge amount of momentum to Dimorphos, to the point where it’s expected to actually change the moonlet’s orbit around Didymos.
This change, to the tune of about 1%, will be detected by ground telescopes within weeks or months. While this may not seem like a lot, 1% is actually a promising shift. If DART were to slam into a lone asteroid, its orbital period around the Sun would change by only about 0.000006%, which would take many years to measure.
So we’ll be able to detect the 1% change from Earth, and meanwhile the pair will continue along its orbit around the Sun. DART will also deploy a small satellite ten days before impact to capture everything.
This is NASA’s first mission dedicated to demonstrating a planetary defence technique. At a cost of US$330 million, it’s relatively cheap in space mission terms. The James Webb Telescope set to launch next month, costs close to US$10 billion.
There will be little to no debris from DART’s impact. We can think of it in terms of a comparable event on Earth; imagine a train parked on the tracks but with no brakes on. Another train comes along and collides with it.
The trains won’t break apart, or destroy one another, but will move off together. The stationary one will gain some speed, and the one impacting it will lose some speed. The trains combine to become a new system with different speeds than before.
So we won’t experience any impact, ripples or debris from the DART mission.
Is the effort really worth it?
Results from the mission will tell us just how much mass and speed is needed to hit an asteroid that may pose a threat in the future. We already track the vast majority of asteroids that come close to Earth, so we would have early warning of any such object.
That said, we have missed objects in the past. In October 2021, Asteroid UA_1 passed about 3,047km from Earth’s surface, over Antarctica. We missed it because it approached from the direction of the Sun. At just 1m in size it wouldn’t have caused much damage, but we should have seen it coming.
Building a deflection system for a potential major asteroid threat would be difficult. We would have to act quickly and hit the target with very good aim.
One candidate for such a system could be the new technology developed by the US spaceflight company SpinLaunch, which has designed technology to launch satellites into orbit at rapid speeds. This device could also be used to fire masses at close-passing asteroids.
Could we really deflect an asteroid heading for Earth? An expert explains NASA’s latest DART mission (2021, November 26)
retrieved 26 November 2021
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'Unsettling': New Study Reveals Arctic Ocean Warming for Over a Century – Common Dreams
New research published Wednesday revealed the Arctic Ocean has been warming for decades longer than scientists previously understood, raising fresh concerns as the polar region faces the growing threat of a total loss of the seasonal ice that is crucial to the survival of the imperiled marine ecosystem.
“We’re talking about the early 1900s, and by then we’ve already been supercharging the atmosphere with carbon dioxide.”
A study published in Science Advances found that “the recent expansion of Atlantic waters into the Arctic Ocean”—a phenomenon knows as “Atlantification”—offers “undisputable evidence of the rapid changes occurring in this region.”
“We reconstruct the history of Atlantification along the eastern Fram Strait during the past 800 years using precisely dated paleoceanographic records,” the study’s authors wrote, referring the the maritime passage between Greenland and Svalbard. “Our results show rapid changes in water mass properties that commenced in the early 20th century—several decades before the documented Atlantification by instrumental records.”
Study co-author Tessi Tommaso of the Institute of Polar Sciences at the National Research Council in Bologna, Italy, said in a statement that “when we looked at the whole 800-year timescale, our temperature and salinity records look pretty constant. But all of a sudden at the start of the 20th century, you get this marked change in temperature and salinity—it really sticks out.”
Francesco Muschitiello—one of the study’s authors and a Cambridge University geographer—told CNN that “the Arctic Ocean has been warming up for much longer than we previously thought. And this is something that’s a bit unsettling for many reasons, especially because the climate models that we use to cast projections of future climate change do not really simulate these type of changes.”
“We’re talking about the early 1900s, and by then we’ve already been supercharging the atmosphere with carbon dioxide,” he continued. “It is possible that the Arctic Ocean is more sensitive to greenhouse gases than previously thought. This will require more research, of course, because we don’t have a solid grip on the actual mechanisms behind this early Atlantification.”
In September, Common Dreams reported that Arctic sea ice shrank to its second-smallest extent since record-keeping began more than four decades ago.
The new study also follows research published September in the journal Earth’s Future showing that the Last Ice Area—which is north of Canada and Greenland and is where the remaining summer sea ice will persist the longest as the climate emergency progresses—could disappear completely by 2100.
“Unfortunately, this is a massive experiment we’re doing,” study co-author Robert Newton, a climate researcher at Columbia University and co-author of the Last Ice Area study, said in a statement. “If the year-round ice goes away, entire ice-dependent ecosystems will collapse, and something new will begin.”
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