Showing posts with label Camp. Show all posts
Showing posts with label Camp. Show all posts

Tuesday, May 10, 2022

Meridians and Time Zones



Longitude is measured by imaginary lines that run around the Earth vertically (up and down) and meet at the North and South PolesThese lines are known as meridians. Each meridian measures one arcdegree of longitude. The distance around the Earth measures 360 degrees.

The prime meridian is the line of 0 longitude, the starting point for measuring distance both east and west around the Earth.

The prime meridian is arbitrary, meaning it could be chosen to be anywhere. Any line of longitude (a meridian) can serve as the 0 longitude line. However, there is an international agreement that the meridian that runs through Greenwich, England, is considered the official prime meridian.



Governments did not always agree that the Greenwich meridian was the prime meridian, making navigation over long distances very difficult. Different countries published maps and charts with longitude based on the meridian passing through their capital city. France would publish maps with 0 longitude running through Paris. Cartographers in China would publish maps with 0 longitude running through Beijing. Even different parts of the same country published materials based on local meridians.

Finally, at an international convention called by U.S. President Chester Arthur in 1884, representatives from 25 countries agreed to pick a single, standard meridian. They chose the meridian passing through the Royal Observatory in Greenwich, England. The Greenwich Meridian became the international standard for the prime meridian.

UTC

The prime meridian also sets Coordinated Universal Time (UTC). UTC never changes for daylight savings or anything else. Just as the prime meridian is the standard for longitude, UTC is the standard for time. All countries and regions measure their time zones according to UTC.

There are 24 time zones in the world. If an event happens at 11:00 a.m. in Houston, Texas, it would be reported at 12 p.m. in Orlando, Florida; 4:00 p.m. in Morocco; 9:00 p.m. in Kolkata, India; and 6:00 a.m. in Honolulu, Hawaii. The event happened at 4:00 p.m. UTC.

The prime meridian also helps establish the International Date Line. The Earth's longitude measures 360, so the halfway point from the prime meridian is the 180 longitude line. The meridian at 180 longitude is commonly known as the International Date Line. As you pass the International Date Line, you either add a day (going west) or subtract a day (going east.)

Hemispheres

The prime meridian and the International Date Line create a circle that divides the Earth into the eastern and western hemispheres. This is similar to the way the Equator serves as the 0 latitude line and divides the Earth into the northern and southern hemispheres.

The eastern hemisphere is east of the prime meridian and west of the International Date Line. Most of Earths landmasses, including all of Asia and Australia, and most of Africa, are part of the eastern hemisphere.

The western hemisphere is west of the prime meridian and east of the International Date Line. The Americas, the western part of the British Isles (including Ireland and Wales), and the northwestern part of Africa are landmasses in the western hemisphere.

Thursday, May 5, 2022

Wolves and the Hunt

 

THE WOLF is a PREDATOR

What the wolf lacks in size, power and weapons it makes up for with collaboration and intelligence. Smaller and less powerful than mountain lions, for example, wolves work together to take down prey much larger than an individual wolf; prey that may otherwise elude them. While individual wolves have been able to subdue large prey animals, their advantage is in collaborating with their pack.

Wolves are opportunists. They test their prey, sensing any weakness or vulnerability through visual cues and even through hearing and scent. Contrary to ambush predators that rely on the element of surprise and a short and intense burst of energy to secure their prey, wolves are endurance or coursing predators. They chase their prey, often over longer distances, sometimes even a few miles, in order to find the right animal or opportunity. On the hunt, wolves work together with certain individuals typically carrying out their specific role in the hunt, often based on age, gender and social standing.

While wolves will eat hares and other small prey, their preferred targets are ungulates, large hoofed animals such as deer and elk. Individual packs will specialize in hunting specific prey species. While most often that is elk, caribou, deer and moose, it can also be bison, muskoxen, small sheep or even salmon.

It is not uncommon for wolves to be injured or even killed during the hunt by being kicked by a hoof or gored by an antler. Most often the prey they select is in some way weaker and/or more vulnerable than the other animals in the herd. They may be injured, sick, old, very young or genetically inferior. But even healthier animals can at times find themselves in a vulnerable position. Over time this process allows the most capable prey animals to survive and pass on their genes and it helps to limit the spread of diseases within the herd. 



THE HUNT

It is during a hunt where co-operation between wolves within a pack is most apparent. A wolf pack may trail a herd of elk, caribou or other large prey for days before making its move. During this time, they are already hunting, assessing the herd, looking for an animal that displays any sign of weakness, and this is just the beginning. Wolves must also factor in other conditions that will affect the hunt; weather and terrain can tip the scales in favor of predator or prey. For example, a wide-open plain favors the ungulates, who, if full-grown and healthy, can outrun the fastest wolf. On the other hand, crusty snow or ice favors the wolves whose wide round paws perform like snowshoes and carry them effortlessly over the surface. An experienced wolf is well aware that hoofed animals break through the crust and can become bogged down in deep snow.

Wolves have learned to use these conditions to their advantage. The late wolf biologist, Dr. Gordon Haber speaks of a particular pack in Alaska that he observed following a herd of caribou on a narrow packed trail through deep snow. The wolves know that their mere presence, following close behind, will eventually panic the caribou. When the rearmost caribou spooks, leaving the hard trail and attempting to run to the middle of the herd, it founders in the snowdrifts. When that happens it is all over. In warm weather, this same pack of wolves changes its tactics, herding the caribou into a dry riverbed where many of the ungulates stumble on the round stones.

A wolf pack therefore weighs many different factors when selecting its target and, as circumstances change during the hunt the target may change as well. Initially they may be pursuing a calf, but if a big healthy bull stumbles unexpectedly, they all know to go after the bigger meal. Conversely, if too many factors seem to favor the prey, they may choose to wait. Sometimes it is better to stay a bit hungry until the odds improve rather than expend precious energy on a fruitless chase.

Other observers of wolves have reported that often fewer than half of wolves on a hunt are actually involved with physically bringing down the prey. The youngest wolves frequently do nothing more than observe and learn from the sidelines. Each of the other pack members contributes according to its particular experience and ability. Speedy, lightly built females often take on herding roles, darting back and forth in front of prey, causing confusion and preventing escape. Slower but more powerful males are able to take down a large animal more aggressively and quickly.

Some of the wolf’s bad reputation stems from the apparent mob scene that ensues when the prey begins to falter. Wolves are not equipped to dispatch their victims quickly; prey usually die of shock, muscle damage or blood loss. If it can, one of the stronger wolves will seize the prey by the nose and hold on tight, helping to bring about a more expeditious end, but the animal can still take many minutes before it succumbs. Equipped only with feet for running and jaws for biting, wolves make the best of their limitations. A wolf pack’s ferocity and apparent brutality is really a defensive measure. It is not rare for a wolf to be seriously injured by flailing hooves and slashing antlers. A well-placed kick could break a wolf’s jaw, rendering it unable to feed itself. It is much safer to harass the prey and let it tire out before moving in close. Far from being a mob scene, a hunt is a masterfully coordinated group effort, well deserving of our admiration.

Although the alpha male is usually in the thick of the hunt, it would be an exaggeration to say that he is leading it. The alpha may select the animal to be pursued, or he may chose to break off the hunt if it is going poorly. But he is not barking out orders to his subordinates like a general on the battlefield. The wolves just seem to know what to do, and they do it as one.

The young wolves watch the behavior of the adults and see how the game is played. They witness how the adults change their strategy according to conditions and type of prey. They learn how the hunters handle each different situation: what to do when the prey dashes for open ground, or jumps into a river, or turns to defend itself.

When juvenile wolves finally join in the hunt, they imitate the more experienced wolves and perfect the precise skills of herding and tackling. By the time they are full grown adults, they have become part of a well-oiled machine. Even if they were able to communicate verbally with each other during the hunt, it would be unnecessary. They know exactly what to expect from the others and what is expected of them.




Tuesday, January 18, 2022

Solar Time vs. Sidereal Time

There is more than one way to measure time. We typically use solar time but we could also also look at sidereal time.

How long does it take Earth to complete a 360-degree rotation? Not quite 24 hours, it turns out - it's precisely 23 hours and 56 minutes.

But because Earth is constantly moving along its orbit around the Sun, a different point on the planet faces the Sun directly at the end of that 360-degree spin.

For the Sun to reach the exact same position in the sky, Earth has to rotate 1 degree further.

That's how humans have chosen to measure days: not by the Earth's exact rotation, but the position of the Sun in the sky.

Technically, these are two different types of day. A day measured by the completion of a 360-degree rotation is called the sidereal day.

A day based on the position of the Sun, however, is a solar day. The latter is four minutes longer than the former, making the even 24 hours we're used to.

"It's only because we move around the Sun in an orbit that the solar day takes 24 hours," James O'Donoghue, a planetary scientist at the Japanese space agency (JAXA), told Business Insider.

"If we didn't orbit the Sun, both days would be the same."

He made the below animation to show how this works. 

Because we go by solar days in our calendars, we count 365 days in a year. But the Earth actually completes a full rotation (a sidereal day) 366 times per year. 

O'Donoghue describes the difference between these two types of day as a matter of choosing which background object we use as a basis of comparison for Earth's rotation. A full rotation relative to the position of the Sun is a solar day. A full rotation relative to all the other stars we see is a sidereal day. 

If we used the sidereal day instead, "the Sun would rise about four minutes earlier every day," O'Donoghue said. "After six months of doing this, the Sun would be rising 12 hours earlier." 

He added: "We've decided to tie our daily rhythm to the Sun, not the stars. In fact, the stars rise about four minutes earlier every day because of our choice."






This article was originally published by 
Business Insider. It has been edited by Soutenus



Ways we measure time:
Solar Time
Universal Time 0 which is abbreviated: UT0 
Universal Time or UT1 
Universal Time or UT 2 or 
Coordinated Universal Time (UTC)
Sidereal Time  (AKA Star Time)
Ephemeris Time