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ATLANTIC SKIES: Much more than a full moon – Learn about the phases of Earth's closest celestial neighbour – TheChronicleHerald.ca

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Although I was wishing the night sky was devoid of the interfering light of the moon on the nights and mornings preceding and following the Perseid meteor shower’s peak dates last week, it did afford me the opportunity to pay closer attention to the slowly-changing phases of the moon.

Most people only notice the full moon, giving little, if any, attention to the other lunar phases. The changing phases of the moon follow a precise timetable, which, once you understand it, might help with your plans, and bolster your interest, to observe the moon.

It is always best to observe the moon, whether with a telescope or binoculars, in its quarter, crescent or gibbous phases. During these phases, the sun’s light strikes the moon at a shallower angle (as opposed to directly, at the full moon phase), highlighting the moon’s terminator (the line between the illuminated and non-illuminated sides), and markedly defining the moon’s mountains, ridges, and impact crater walls.

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A lunar phase is defined as the shape of the sunlit portion of the moon’s surface as seen from Earth. The moon completely orbits the Earth in an average time of 29.5 days (referred to as a “synodic month” or a “lunation”), marking, essentially, the period between consecutive new moon phases.

Due to variations in the angular rate at which the Earth orbits the sun (based on the fact that the Earth’s orbital path around the sun is elliptical, rather than circular, in shape), the actual time between lunations varies between 29.18 days and 29.93 days (the average being 29.530588 days, or 29 days, 12 hours, 44 minutes, and 2.8 seconds).

As the moon orbits the Earth, and as the Earth orbits the sun (also an elliptical path), the area of the sunlit portion of the moon changes. As discussed in one of my earlier columns, gravity tidally locks one side (or face) of the moon towards Earth. Each moon phase depends on the position of the moon relative to the sun as seen from Earth, and the portion of the Earth-facing side that is illuminated by the sun.

There are four distinct lunar phases, with an average of 7.38 days between each of these phases. The first phase, the new moon, is when the sun and the moon are aligned on the same side (called a “conjunction”) of Earth. During this time, the moon is too close to the sun to be seen, and the side of the moon facing Earth is not illuminated by the sun (though, in fact, it is faintly lit by “earthshine”, which is washed out by the sun’s light). In the northern hemisphere, the new moon rises around 6 a.m., and sets around 6 p.m.

The next distinct lunar phase is the first-quarter moon, where the moon’s right side is 50 per cent lit by the sun. In the northern hemisphere, first-quarter moons are visible in the afternoon and early evening skies, rising around noon and setting around midnight.

Next is the full moon, with 100 per cent of its Earth-facing side illuminated. Full moons rise at sunset and set at sunrise.

The fourth lunar phase is the last-quarter moon, with 50 per cent of its left side illuminated. A last-quarter moon, visible from late night through the following morning, rises around midnight and sets around noon. It should be noted that the actual timing of the phases in the sky, and their location along the horizon, will vary with the latitude of the observer.

Between the four major phases, there are a number of intermediate phases: between the new moon and the first-quarter moon is the waxing (thickening), crescent moon (right side one to 49.9 per cent lit); between the first-quarter moon and the full moon is the waxing, gibbous moon (right side 50.1-99.9 per cent lit); between the full moon and the last-quarter moon is the waning (thinning), gibbous moon (left side 99.9- 50.1 per cent lit); and between the last-quarter moon and the new moon is the waning, crescent moon (left side 49.9 – 0.1 per cent lit).

If you’ve ever heard the phrase, “the old moon in the new moon’s arms,” this refers to when the waning, crescent moon has shrunk to just a thin sliver. Also, the crescent moon (either waxing or waning) is sometimes referred to as the “Cheshire Cat Moon”, as it resembles, at some point, the glowing smile that the Cheshire Cat left hanging in the air when it disappeared whilst talking with Alice (in ‘Alice in Wonderland’).

On a clear night, look for “earthshine” on the unlit, back portion of the crescent moon – a faint illumination caused by indirect sunlight reflecting off Earth’s lit half striking that dark side.


This week’s sky

Mercury achieves superior solar conjunction (passes behind the sun as seen from Earth) on Aug. 17, and is not observable. Mars (magnitude -1.47) rises in the east around 11:30 p.m., reaching its highest point (49 degrees) in the southern sky shortly after 5 a.m., before being lost in the dawn twilight 47 degrees above the southern horizon by about 6 a.m.

Mighty Jupiter (magnitude -2.65) is visible in the southeast sky around 8:30 p.m., reaching 21 degrees above the southern horizon by 10:45 p.m., before sinking below eight degrees above the southwest horizon shortly after 2 a.m.

Saturn (magnitude +0.23) trails Jupiter across the evening sky, becoming visible to the left of the larger and brighter planet around 8:45 p.m., remaining visible until it, too, disappears from view as it sinks below 10 degrees above the southwest horizon around 2:30 a.m.

Until next week, clear skies.


Events

Aug. 17 – Mercury reaches superior solar conjunction

Aug. 18 – New moon

Aug. 20 – Moon at perihelion (closest approach to the sun)

Aug. 21 – Moon at perigee (closest approach to Earth)

Glenn K. Roberts lives in Stratford, P.E.I., and has been an avid amateur astronomer since he was a small child. He welcomes comments from readers at glennkroberts@gmail.com.

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Giant prehistoric salmon had tusk-like teeth for defence, building nests

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The artwork and publicity materials showcasing a giant salmon that lived five million years ago were ready to go to promote a new exhibit, when the discovery of two fossilized skulls immediately changed what researchers knew about the fish.

Initial fossil discoveries of the 2.7-metre-long salmon in Oregon in the 1970s were incomplete and had led researchers to mistakenly suggest the fish had fang-like teeth.

It was dubbed the “sabre-toothed salmon” and became a kind of mascot for the Museum of Natural and Cultural History at the University of Oregon, says researcher Edward Davis.

But then came discovery of two skulls in 2014.

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Davis, a member of the team that found the skulls, says it wasn’t until they got back to the lab that he realized the significance of the discovery that has led to the renaming of the fish in a new, peer-reviewed study.

“There were these two skulls staring at me with sideways teeth,” says Davis, an associate professor in the department of earth sciences at the university.

In that position, the tusk-like teeth could not have been used for biting, he says.

“That was definitely a surprising moment,” says Davis, who serves as director of the Condon Fossil Collection at the university’s Museum of Natural and Cultural History.

“I realized that all of the artwork and all of the publicity materials and bumper stickers and buttons and T-shirts we had just made two months prior, for the new exhibit, were all out of date,” he says with a laugh.

Davis is co-author of the new study in the journal PLOS One, which renames the giant fish the “spike-toothed salmon.”

It says the salmon used the tusk-like spikes for building nests to spawn, and as defence mechanisms against predators and other salmon.

The salmon lived about five million years ago at a time when Earth was transitioning from warmer to relatively cooler conditions, Davis says.

It’s hard to know exactly why the relatives of today’s sockeye went extinct, but Davis says the cooler conditions would have affected the productivity of the Pacific Ocean and the amount of rain feeding rivers that served as their spawning areas.

Another co-author, Brian Sidlauskas, says a fish the size of the spike-toothed salmon must have been targeted by predators such as killer whales or sharks.

“I like to think … it’s almost like a sledgehammer, these salmon swinging their head back and forth in order to fend off things that might want to feast on them,” he says.

Sidlauskas says analysis by the lead author of the paper, Kerin Claeson, found both male and female salmon had the “multi-functional” spike-tooth feature.

“That’s part of our reason for hypothesizing that this tooth is multi-functional … It could easily be for digging out nests,” he says.

“Think about how big the (nest) would have to be for an animal of this size, and then carving it out in what’s probably pretty shallow water; and so having an extra digging tool attached to your head could be really useful.”

Sidlauskas says the giant salmon help researchers understand the boundaries of what’s possible with the evolution of salmon, but they also capture the human imagination and a sense of wonder about what’s possible on Earth.

“I think it helps us value a little more what we do still have, or I hope that it does. That animal is no longer with us, but it is a product of the same biosphere that sustains us.”

This report by The Canadian Press was first published April 24, 2024.

Brenna Owen, The Canadian Press

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Giant prehistoric salmon had tusk-like spikes used for defence, building nests: study

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A new paper says a giant salmon that lived five million years ago in the coastal waters of the Pacific Northwest used tusk-like spikes as defense mechanisms and for building nests to spawn.

The initial fossil discoveries of the 2.7-metre-long salmon in Oregon in the 1970s were incomplete and led researchers to suggest the fish had fang-like teeth.

The now-extinct fish was dubbed the “saber-tooth salmon,” but the study published in the peer-reviewed journal PLOS One today renames it the “spike-toothed salmon” and says both males and females possessed the “multifunctional” feature.

Study co-author Edward Davis says the revelation about the tusk-like teeth came after the discovery of fossilized skulls at a site in Oregon in 2014.

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Davis, an associate professor in the department of earth sciences at the University of Oregon, says he was surprised to see the skulls had “sideways teeth.”

Contrary to the belief since the 1970s, he says the teeth couldn’t have been used for any kind of biting.

“That was definitely a surprising moment,” Davis says of the fossil discovery in 2014. “I realized that all of the artwork and all of the publicity materials … we had just made two months prior, for the new exhibit, were all out of date.”

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SpaceX sends 23 Starlink satellites into low-Earth orbit

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April 23 (UPI) — SpaceX launched 23 Starlink satellites into low-Earth orbit Tuesday evening from Space Launch Complex 40 at Cape Canaveral Space Force Station in Florida.

Liftoff occurred at 6:17 EDT with a SpaceX Falcon 9 rocket sending the payload of 23 Starlink satellites into orbit.

The Falcon 9 rocket’s first-stage booster landed on an autonomous drone ship in the Atlantic Ocean after separating from the rocket’s second stage and its payload.

The entire mission was scheduled to take about an hour and 5 minutes to complete from launch to satellite deployment.

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The mission was the ninth flight for the first-stage booster that previously completed five Starlink satellite-deployment missions and three other missions.

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