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ATLANTIC SKIES: How bright do the stars shine? The magnitude system explained – TheChronicleHerald.ca

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Some of my readers have queried me as to why the brighter objects in the night sky have negative magnitude values, while the fainter ones have positive values, when, logically (at least to them), it should be the other way around.

For this seemingly “backward” rating system, we can thank the ancient Greek astronomer Hipparchus, who, in 129 BC, drew up the first recognized star chart. On this chart, he listed the magnitude (from Latin magnitudo or magnus meaning “great”) of the stars he could see in the night sky. Hipparchus listed the brightest stars that he could see with his naked eye as magnitude +1.0 stars, those half as bright as the magnitude +1.0 stars as magnitude 2.0 stars, and so on, until reaching magnitude +6.0, the faintest he could see.

His magnitude scale remained in use for rating the brightness of the stars (and other celestial objects by comparison) for the next 1,400 years. It wasn’t until 1609, when Italian astronomer Galileo (1564-1642) developed his first telescope and observed much fainter stars than those listed on the star charts in use at that time, that the magnitude scale was extended (with ascending positive numbers) to include the fainter stars.

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In the mid-1850s, when astronomers discovered that some magnitude +1.0 stars are brighter than others, the scale was again extended outward, this time with ascending negative values to reflect the brighter stars.

The stars Rigel (Orion), Capella (Auriga), Arcturus (Bootes), and Vega (Lyra) were listed at magnitude 0.0, while stars brighter than these were given negative values. Sirius, the brightest star in the night sky, is rated at magnitude -1.43 , while our sun is rated at magnitude -26.7.

Planets and other celestial objects can also be rated on the magnitude scale. Venus, at its brightest, shines at magnitude -4.4, while the full moon beams (on average) at magnitude -12.6.

The faintest stars that the average human, naked-eye can see (under a clear sky from a dark site) is magnitude +6.0, while binoculars can boost that to magnitude +10. In contrast, the Hubble Space Telescope can see stars as faint as magnitude +30.

With stronger telescopes, the magnitude scale for stars was again adjusted.

 

What does it mean?

A star’s apparent brightness or luminosity refers to the amount of light energy (from thermonuclear fusion within the star’s core) it emits, and how much of that energy passes per second through a square meter of the star’s surface area. Basically, how bright a star appears depends on how much of its light energy per second strikes the area of a light detector (in our case, the human eye). The apparent brightness we see or measure is inversely proportional to the square of our distance from the star, with the apparent brightness diminishing as the distance squares.

Astronomers use the terms “apparent magnitude” and “absolute magnitude” when denoting a star’s brightness. Apparent magnitude is how bright the star appears to an Earth-bound observer, and is directly related to a star’s apparent brightness.

Stellar measurements in the 19th century indicated that magnitude +1.0 stars are approximately 100 times brighter than magnitude +6.0 stars (i.e., it would take 100 magnitude +6.0 stars to provide as much light as a single magnitude +1.0 star). Subsequently, the stellar magnitude scale was modified so that a magnitude difference of five corresponded exactly to a factor of 100 times difference in brightness., while a difference of one magnitude equaled a difference factor of 2.512 in brightness.

This resulting stellar magnitude rating system was based on a logarithmic scale, with whole numbers, and fractions thereof, indicating varying ratios of brightness (e.g., 0 = 1 to 1; 0.2 = 1.2 to 1; 0.5 = 1.6 to 1; 1 = 2.5 to 1; 5 = 100 to 1, etc.). A star’s apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any dimness of the star’s light caused by the interference of interstellar dust along the line of sight of the observer.

When astronomers want to measure how intrinsically bright a star is regardless of its distance from Earth, they measure the star’s absolute magnitude, or its apparent magnitude if all the stars it is being compared to were placed at 10 parsecs distance from Earth. With one parsec equaling 3.26 light-years (a light-year is the distance light travels through the vacuum of space in one year; approximately 10 trillion kilometres), 10 parsecs equals 32.6 light-years, or approximately 100 trillion kms. A star’s absolute magnitude measures its true energy output (its luminosity).

As with the apparent magnitude scale, the absolute magnitude scale is also “backward”, giving less luminous stars ascending positive values, and more luminous stars ascending negative ones. For celestial objects such as comets and asteroids, the absolute magnitude scale (also with positive through negative values) is based on how bright the object would appear to an observer standing on the sun if the object were 1 AU (149,597,871 kms) away.

This week’s sky

Mercury (magnitude -0.8) is visible low (about eight degrees) above the northwest horizon shortly after 9 p.m., before dropping from view shortly after 10 p.m. This bright but small planet (heading towards its greatest eastern elongation from the sun on June 2) achieves an altitude of 18 degrees in the evening sky by May 31. It reaches its half-phase (called dichotomy) on May 29.

Venus (magnitude -4.3) appears only about 13 degrees above the western horizon shortly after 9 p.m., before setting shortly before 11 p.m.

Jupiter (magnitude -2.5) rises in the southeastern sky shortly before 1 a.m., reaching 22 degrees height in the southern sky before fading from view around 5:15 a.m.

Saturn (magnitude +0.48) follows Jupiter into the southeastern dawn sky around 1 a.m., rising to about 23 degrees above the southern horizon before it fades from sight shortly before 5 a.m.

Mars (magnitude +0.16) rises in the southeast around 2:30 a.m., reaching an altitude of about 20 degrees above the horizon before fading from view a few minutes before 5 a.m.

Currently at magnitude +4.5, Comet C/2020 F8 SWAN is now in the constellation of Perseus – the Warrior Prince. This fading comet will be difficult to see, as it reaches an altitude of only about 10 degrees above the northeastern horizon between 4 a.m. and 5 a.m., before the glow of the rising sun overtakes it. With clear skies and an unobstructed view of the northeastern horizon, it might still be seen in binoculars and small scopes.

Until next week, clear skies.


Events:

May 29 – Mercury reaches dichotomy

May 30 – First quarter moon

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, and anyone who would like to do so is encouraged to email him at glennkroberts@gmail.com.

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SpaceX launch marks 300th successful booster landing – Phys.org

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Credit: Unsplash/CC0 Public Domain

SpaceX sent up the 30th launch from the Space Coast for the year on the evening of April 23, a mission that also featured the company’s 300th successful booster recovery.

A Falcon 9 rocket carrying 23 of SpaceX’s Starlink internet satellites blasted off at 6:17 p.m. Eastern time from Cape Canaveral Space Force Station’s Space Launch Complex 40.

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The first-stage booster set a milestone of the 300th time a Falcon 9 or Falcon Heavy booster made a successful recovery landing, and the 270th time SpaceX has reflown a booster.

This particular booster made its ninth trip to space, a resume that includes one human spaceflight, Crew-6. It made its latest recovery landing downrange on the droneship Just Read the Instructions in the Atlantic Ocean.

The company’s first successful booster recovery came in December 2015, and it has not had a failed booster landing since February 2021.

The current record holder for flights flew 11 days ago making its 20th trip off the .

SpaceX has been responsible for all but two of the launches this year from either Kennedy Space Center or Cape Canaveral with United Launch Alliance having launched the other two.

SpaceX could knock out more launches before the end of the month, putting the Space Coast on pace to hit more than 90 by the end of the year, but the rate of launches by SpaceX is also set to pick up for the remainder of the year with some turnaround times at the Cape’s SLC-40 coming in less than three days.

That could amp up frequency so the Space Coast could surpass 100 launches before the end of the year, with the majority coming from SpaceX. It hosted 72 launches in 2023.

More launches from ULA are on tap as well, though, including the May 6 launch atop an Atlas V rocket of the Boeing CST-100 Starliner with a pair of NASA astronauts to the International Space Station.

ULA is also preparing for the second launch ever of its new Vulcan Centaur rocket, which recently received its second Blue Origin BE-4 engine and is just waiting on the payload, Sierra Space’s Dream Chaser spacecraft, to make its way to the Space Coast.

Blue Origin has its own it wants to launch this year as well, with New Glenn making its debut as early as September, according to SLD 45’s range manifest.

2024 Orlando Sentinel. Distributed by Tribune Content Agency, LLC.

Citation:
SpaceX launch marks 300th successful booster landing (2024, April 24)
retrieved 24 April 2024
from https://phys.org/news/2024-04-spacex-300th-successful-booster.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
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Wildlife Wednesday: loons are suffering as water clarity diminishes – Canadian Geographic

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The common loon, that icon of northern wilderness, is under threat from climate change due to declining water clarity. Published earlier this month in the journal Ecology, a study conducted by biologists from Chapman University and Rensselaer Polytechnic Institute in the U.S. has demonstrated the first clear evidence of an effect of climate change on this species whose distinct call is so tied to the soundscape of Canada’s lakes and wetlands.

Through the course of their research, the scientists found that July rainfall results in reduced July water clarify in loon territories in Northern Wisconsin. In turn, this makes it difficult for adult loons to find and capture their prey — mainly small fish — underwater, meaning they are unable to meet their chicks’ metabolic needs. Undernourished, the chicks face higher mortality rates. The consistent foraging techniques used by loons across their range means this impact is likely echoed wherever they are found — from Alaska to Canada to Iceland.

The researchers used Landsat imagery to find that there has been a 25-year consistent decline in water clarity, and during this period, body weights of adult loon and chicks alike have also declined. With July being the month of most rapid growth in young loons, the study also pinpointed water clarity in July as being the greatest predictor of loon body weight. 

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One explanation for why heavier rainfall leads to reduced water clarity is the rain might carry dissolved organic matter into lakes from adjacent streams and shoreline areas. Lawn fertilizers, pet waste and septic system leaks may also be to blame.

The researchers, led by Chapman University professor Walter Piper, hope to use these insights to further conservation efforts for this bird Piper describes as both “so beloved and so poorly understood.”

Return of the king

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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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