How is visibility determined in weather reports?

One way would be for two people communicating wirelessly to start in a wide-open area and start walking until they could no longer see each other. Of course this is ridiculous. The way it’s usually done, by airports and such, is by looking at predetermined landmarks of known distances. Daytime visibility is defined as the distance in which is is possible to see and identify, with the naked eye, “a prominent dark object against the sky at the horizon.” Read more…

How Can I Tell What Kind of Tadpoles I Have?

This is a tricky question and one that has befuddled many biologists for a long time. The easiest way, but not always 100% accurate, would be to find a frog near where you found the tadpoles and there’s a good chance they are the same species. If you can’t find an adult frog, do a little research on the amphibious wildlife indigenous to your area and you may be able to narrow it down a bit more. This won’t always give you a firm answer, as many areas will have several native species of frogs.

A more scientific method is through close observation and comparing your tadpole to a known chart. The below images and chart should help you get started.

First, where are the eyes? Are they lateral or dorsal?

Next, check the vent location. You may have to hold the tadpole Read more…

Who came up with the phrase “survival of the fittest?”

While many people associate this phrase with Darwinism, and rightfully so, it was actually coined by the English sociologist Herbert Spencer (1820-1903). It is one of the principles of Darwin’s Natural Selection theory that basically says that animals that are less well-adapted to their environment are less likely to survive (and propagate their species) than are better-adapted animals.

Do dogs only see in black and white?

Not entirely. It is generally agreed that dogs can distinguish fewer colors than humans, but their vision isn’t entirely restricted to black and white. Rods and cones are the two types of receptors in the retina that most of us have heard of. The rods are more light sensitive and help for seeing in low light conditions. The cones help with focusing on more detailed objects and are what help distinguish between colors.

A dog’s retina has a much higher proportion of rods than cones than the human retina. This is why we can see more details at a longer distance than our dogs, but they can see better than we can in low light conditions. One estimate is that a dog can see at about 25 yards what we can see at 75 yards. If this is the case, we could call a dog’s vision 20/75 on the standard 20/20 scale. Of course these are estimates as it would be pretty difficult to get a dog to read an eye chart at any distance.

So why did the dog’s and man’s retinas evolve this way? Most likely because it was more advantageous for the dog to be able to see in low light conditions. The nearest wild relative to the dog is the wolf, which often hunts near the hours around dawn and dusk. Many predators hunker down during the middle of the day and thus don’t need to have the best vision in this time. Man evolved from any nocturnal habits such as these millions of years ago and has likewise benefited from having better daytime vision- ie., we have evolved to have more cones than rods.

Source: Wikipedia’s entry on dogs, eyesight.

Why do AM radio stations broadcast farther at night?

The short answer is because of the nature of the ionosphere of the Earth. The ionosphere consists of several different layers of gases that have become conductive from the bombardment of the atoms by: solar radiation, by electrons and protons emitted by the sun, and by cosmic rays.

These layers, sometimes called the Kennelly-Heaviside layer, reflect AM radio signals, thus enabling AM broadcasts to be received by radios that are a long way from the transmitting station. At night, the ionosphere layers partially dissipate and become an excellent reflector of the short waveband AM radio waves.

Source: The Handy Science Answer Book.

Who discovered Mars?

No one person is considered to have discovered Mars. As it is very bright in the night sky, it has been visible since the first humans gazed up to the heavens. What we do know is that it was named after the Roman god of war- presumably because of its red color which may have reminded our ancestors of blood.

1659: Christian Huygens discovered the dark spot located in the boundary between the northern lowlands and southern highlands of the planet. It was later called the Syrtis Major.

1877: Astronomer Giovanni Schiaparelli discovered what he believed to be several lines crossing one another. He claimed they were water canals made by intelligent creatures.

1877: Astronomer Asaph Hall spotted the two moons and named them Phobos and Deimos (fear and panic). He named them after the mythical horses that pulled the chariot of the Roman god, Mars.

1971: Mariner 9 returned images of Martian volcanoes and canyons. It discovered Olympus Mons, a massive volcano towering over 15 miles above the surface. Mariner 9 also found evidence that water once flowed on Mars. There were no sightings of Schiaparelli’s famous canals.

1975: Viking I and II spacecraft landed on Mars to study its surface. They analyzed the rocks and soil of the planet while providing us with information about its atmosphere and weather patterns.

Source: Wikipedia and the University Corporation for Atmospheric Research.

Is a dog’s mouth really cleaner than a human’s?

The short answer is no. While this myth seems to have been around a while, it has been debunked by several reputable articles over the years. According to ABC News, the mouth of a typical dog is full of bacteria but it is “species specific” so the bacteria inside a dog’s mouth may be completely harmless to us. Read more…