Why do leaves turn yellow?

With the last days of summer and the beginning of autumn, I’ve decided to talk about trees. In particular, why they change colour as winter creeps closer.

Leaves are green because they have chlorophyll, a pigment that helps them absorb sunlight and photosynthesize. But chlorophyll is not the only pigment in plants, they also contain carotenoids, which colour them yellow, orange or red. 

  

Usually, chlorophylls is dominant, as it is the most efficient at absorbing the spectrum, but as winter approaches and the days grow shorter, photosynthesis is no longer as profitable. So to limit losses, plants stop producing chlorophyll and re-absorb that which is already in the leaves. As a result, for the short moment before they die and fall off, the carotenoids are revealed painting the trees red, orange and yellow.

References and additional reads:

Wonderopolis: Why Do Leaves Change Colour in Autumn?

WDNR: Why Do Leaves Change Colour?

ESF: Why Leaves Change Colour

USDA: Why Leaves Change Colour

Why do we have seasons?

Have you ever wondered, as you watched the snow fall or basked in the summer sun, why is it that we have seasons? Why does water freeze into snowflakes at times while at others suffocates us with humid vapour.

What directs the drastic shifts in climate every spring or fall? No, it’s not because we revolve closer or further from the sun as many believe, the difference in the slightly elliptical orbit is not enough to cause heat changes.

We have seasons because our planet is tilted and at different times of the year the warm sunlight reaches the ground differently.

In the winter, not only are the days fleeting and short, but sunlight fall at an angle, failing to provide enough warmth to warm us up. Meanwhile, in the opposite hemisphere, light descends straight and the days are long and warm.

As for spring and fall, it is the time when the sun shines equally on both hemispheres, gifting us soft, temperate weather.

 

References and related reads:

SciJinks: Why does the Earth have seasons?

Woodland Junior School: Why do we have Seasons?

Nasa: What causes the seasons?

Everyday Mysteries: Why is it hot in summer and cold in winter?

Youtube: SciShow - Why do we have seasons?

Why do deserts form?

 

Last week we spoke of sandy beaches along the vast seas… And today we take a look at a different kind of oceans, the endless expanse of dunes we know as desert.

Much like on the beach, in the desert sand due to erosion, inheriting the colour of the rocks and soil and varying in consistency according to the extent of weathering. Unlike our favourite summer destination, however, deserts are the last thing we want to spend our vacation in unless it’s to see the pyramids or the spring blooms.

Photo by Winfried Bruenken

Photo by Javier Rubilar

Deserts can be cold or hot and equally unfriendly to the majority of living beings, but how do they form and conquer so much land?

A variety of conditions and reasons lead to the formation of deserts but by far the most important are distance from the ocean and the presence of natural barriers such as mountains. The further we get from the seas, the dryer the air becomes as moisture is absorbed by the land and plants along the way leading to little or no rainfall in the inner areas. Mountains, like the Andes or the Himalayas, are also excellent shields against moisture, trapping clouds to one side and leaving the other dry.

Desertification also depends on the winds, dryer, hotter winds in the equatorial zones can slowly erode the land into finer and finer sand. These winds prevent the formation of clouds and the dryer the area becomes, the fewer the plants keeping the soil together. The more sand is formed due to erosion, the stronger the wind erosion becomes as sand is carried on, grinding down hills and suffocating plant life.

Or at least that’s the simple version. Deserts may be hot or cold, covered in sand, pebbled stone or even ice, they can have little to no vegetation or a cover of low grasses, what they all have in common is the aridity. Whether no rain falls, or the land and air are unable to preserve moisture, the lack of surface water leads to scarcity of plants and large empty planes of sand or ice dunes.

References and additional reads:

National Geographic Encyclopedia: Desert

Bright Hub: Learn How Deserts Came Into Existence

St. Mary College Media: How are deserts made?

Geology Class: The Geology of Deserts

Wikipedia: Desert

What determines the colour of sand?

If there was one place we’d rather be on a hot summer day, other than a well air conditioned room, it’s the beach. Palm trees, clear skies, pristine waters, and golden sands as far as the eye can see.

Or maybe white sands, orange, or black, or red, or even green. Beaches come in many shades. So what determines their colour, and the colour of sand in general?

The short answer is the geology of the region.

Sand is composed of fine particles formed when rocks and minerals are weathered down and eroded. In Hawaii or Iceland we find black sands formed by lava rocks like basalt. In other places we see red beaches because of the high iron content in the soil. Beyond rocks and soils, common ingredients are shells, corals or minerals like quartz that give the sand a pink or even pristine white hue.

Usually sand is a mixture of different types of minerals and rocks that make it brown or tan in colour but when we have a dominant or single source of formation, we may get  quite vivid colours.

References and related reads:

Wikipedia: Sand

Coastal Care: Beach Basics

Rock Cycle lab: Analyzing the Origin of Different Sands

Tourism on the Edge: World’s Most Beautiful Colorful Sand Beaches

Pictures: Spectacular Sand Beaches in a Rainbow of 10 Incredible Colors

How does caffeine affect us?

The sun is rising, the birds are singing, and traffic is starting to hum outside your window. It’s a brand new day and most of you probably won’t even crawl out of bed without a hot cup of coffee waiting in the kitchen.

Drinking coffee has not only become a daily routine for many, but also a ritual ingrained in culture and history. People gather to chat over coffee, drink it with breakfast or dessert. Some mythologies incorporate it, and many economies depend on it.

But why has coffee become such a big thing? What has made it into one of the primary substances consumed, almost on par with sugar?

Taste certainly has a part in it, but mostly coffee is favoured for its properties. In a busy world where you need to get up early and remain at your best through the day, it is irreplaceable. Coffee is considered a stimulant, keeping you awake, alert, and energetic.

How does this work exactly?

When the brain prepares to rest, a chemical called adenosine binds to specific receptors signaling you to feel tired, slowing down nerve impulses and gently guiding you to sleep. Caffeine has a very similar structure to adenosine, tricking the receptors into binding it instead. As caffeine intake reaches its peak, it outcompetes adenosine, preventing the brain from feeling fatigued. It also increases the heart rate and prepares the muscles for action, leaving you ready to face the day.

But for all the benefits, caffeine comes with an equal amount of drawbacks. Like any other drug, it can lead to addiction and withdrawal, even if weak, when consumption is interrupted. Some of the side effects include anxiety, insomnia, restlessness, upset stomach, irritability, and dizziness. And while coffee can alleviate headaches and migraines, habitual drinking can actually cause them.

You may feel energetic, but that feeling is a false one. Caffeine tricks the body into using up its energy reserves, which can leave you extra tired once it leaves the system.

Despite all, coffee is still the preferred morning beverage and drank reasonably in moderation can provide more good than harm.

References and related reads:

The Independent: Under the Microscope: How does caffeine work?

MedicalNewsToday: What is caffeine? How does it work?

mental_floss: How Does Caffeine Work?

howstuffworks: Why does caffeine keep you awake?

LifeHacker: What Caffeine Actually Does to Your Brain

Wikipedia: Coffee

Why does the road appear wet when it's hot?

There’s no better time for a road trip than summer. But while they always lead us to exciting destinations, the journey itself can be quite laborious and hot. For hours, you may be stuck in a car, mindlessly looking out of the window, dozing off, or even driving. Sometimes in the heat of the day, a shimmery haze appears on the horizon as if water or even oil have been spilled all over. Yet there’s not a single cloud in the sky, and once you approach and drive past, the highway is as dry as it has been and the puddle has moved on.

Everyone who has observed asphalt in the summer has seen this phenomenon. It is called heat haze, an inferior mirage since it appears under the real object.

But how exactly does it form?

Under the sun, asphalt is much akin to a stove top, radiating heat and even capable of frying eggs if necessary. It turns the air drifting over it into a nice warm blanket that clings to the ground.

Like any optical mirages, the vision is caused by the way light travels through substances. Different media, including different atmospheric conditions, allow and bend light differently.

When it hits this border between the hot air of the asphalt and the cooler air above, the rays are refracted. What we see is the sky lying on the road because of how light is bent and redirected but our brain interprets it as water. Due to this refraction we may also see cars as if reflected in the surface underneath strengthening the illusion of water.

This phenomenon is also why we see oases and mirages in the desert.

Resources and additional reads:

Wikipedia: Mirage

PhysLink: What is the mirage effect?

thePhysicsClassroom: Mirages

MentalFloss: Why Does the Road Look Wet on Hot Days?

Where is our shadow on a cloudy day?

Wherever we go, whatever we do, we’re always accompanied by a silent companion. Sometimes it’s quite dark and visible, and others it hides among its kind, but our shadow is forever bonded to us. Still, on certain overcast days, we may look around and notice that we are alone.

Where does our shadow go when the sky is cloudy grey?

Shadows are an optical effect caused by an object when it obscures the light source. And when there are many light sources, there can be many shadows.

A shadow such a common, everyday, thing that we may simply stop noticing it until it’s gone. Yet, it is also mysterious, so much so that we write and muse, and make metaphors out of it. In literature, some have written about the importance of a shadow, and how lacking it will make people shun and avoid you. And in art, shadows are essential, without them the picture may feel odd, unnerving, or simply lacking in some unfathomable way.

So what happens on a cloudy day? Light still streams from the sky, and we see our surroundings perfectly, so why are shadows faint or nonexistent?

Similar to how rainbows form after rain, the water droplets in the clouds diffuse most of the visible light, colouring the clouds white to darker and darker grey depending on their size and depth.

And as this mass of clouds scatters the sunrays, there simply isn’t a concentrated light source in the sky, and objects on the ground cast very faint or even no shadows. But while most of the sun’s radiation, and therefore visible light, are diffused or reflected, clouds don’t make UV rays any less dangerous and sunburn is still possible.

As for our constant companion, it return the moment a sunray touches the ground.

Resources and related reads:

Wikipedia: Shadows

University of Illinois: Scattering of Light

Hanover College: Shadow

American Scientist: Sunshine on a Cloudy Day

How does heat affect us?

You leisurely lounge at home on a summer afternoon, maybe the cooling is on, or a light breeze dances in the air but the heat still lingers, weighing you down. No matter what you do, where you turn, how many clothes you take off or cool drinks you chug, it always finds its way, wrapping you in a tight, warm blanket.

 

And when the heat becomes extreme, it can provoke quite radical physical reactions in the body, varying from flushing, sweating, dehydration, fatigue, nausea, headaches, cramps to even more serious illness and death.

Areas with high humidity make matters even worse because sweating and breathing are not as effective at cooling the body. In other words, as awesome as summer is, it should not be underestimated and precautions should be taken against the sneaky heat.

But what about some of the more subtle ways the sizzling summer days affect us? Heat makes our bodies unhappy and as a result, our mind isn’t at its perkiest either. First, our concentration suffers as it becomes increasingly difficult to focus on any brain related work beyond chanting ‘oh god its freaking hot’ in a loop. But not only do we feel extra lazy, but also more anxious and irritable, ready to snap at anything and anyone unless they come bearing gifts in the form of cool drinks or ice cream.

And the worst part is, there’s no escape this hellish nightmare other than sticking to air conditioned spaces, wearing as little clothing as possible, soaking in a pool, and making sure the soda on ice keeps coming.

References and additional reads:

National Weather Service: Health and Safety PDF

CBCNews: Too hot for your health, How heat affects the body

Scientific American: How Does a Heat Wave Affect the Human Body?

UoC, Division of Agriculture and Natural Resources: How heat affects the body

How good is the Sun for us?

Nothing is more pleasant than sunlight warming our skin on a cool morning, or enveloping us on a cold day. And in summer, the sight of the sea and the beach are most beautiful under the light of the blazing sky fireball.

There’s no doubt our planet, and everything living on it, owe its existence to the sun, but how good exactly is sunlight for us?

Whether nagged by our mothers nag to get some sunlight, or we just feel drawn to the brightness, choosing to sunbathe in the park or on the beach, there’s a very good reason to spend some time in the light. Even the darkest of souls and vampires at heart crave for the sun at times, maybe not always realizing the benefits, but definitely lured by its brightness.

    The most important asset of sunlight is that it kicks up the production of Vitamin D, which in turn helps us grow strong, durable bones, which can be crucial for children and the elderly.

The sun also affects our mood, brightening even the darker days and fights off disease because it kills germs, leaving us healthier and happier.

But scorching hot sunlight can be just as dangerous. The key here is that some sun is good, but too much and the benefits turn to injury. The UV rays in the sunlight can actually damage the skin, cause wrinkles, spots and increase the risk of skin cancer. This is because UV radiation can damage the DNA of the skin cells preventing them from dividing correctly.

Of course, with the right protection and mindful exposure, the sun becomes just another of the pleasures of summer.

Resources and additional reads:

LifeScience: Some Sun Exposure Might be Good for Health

Patient: Sun and Health

Softpedia: 10 Reasons Why Sun is Good for our Health

HowStuffWorks: Can the sun make me happy?

Why is the sea salty?

Most of you have at one point or another gone to the seaside, chased around jellyfish, filled all crevices with sand, and maybe gotten a nasty sunburn. Through your merry beach adventures, you’ve no doubt discovered, or confirmed, the simple fact that seawater is salty.

And that may seem normal, it’s such a common knowledge we don’t really question it at first. But if we think about it, rain, rivers, and even ice caps are all made out of fresh water, yet they flow in or rest onto the sea. So why is it salty?

 

A long, long time ago when the earth was still young and hot, volcanoes continuously pumped noxious gases into the atmosphere. Along with the greenhouse gases and heavy particles, water vapour floated in the air. So when the planet cooled and the first clouds formed century long rains brought everything down into the lowlands. Gases dissolved, particles fell, and the new oceans obtained their particular flavour.

But back then, they were not as salty as they are today.

Through the years, as all those rains fell, and all the rivers carried water down the rocky slopes, minerals gradually eroded and washed down, accumulating into the oceans. The largest source of the salt we find in the seas today is this kind of erosion.

(One of these minerals is gold. We actually find more in the ocean than there is on land, but extracting it is so expensive, it’s far more profitable to leave it alone.)

Additionally, underwater volcanoes keep spitting gases and minerals into the oceans even today.

And finally, water constantly escapes the seas through evaporation, leaving behind the heavier particles, and returning to the land to wash away even more salts. A process known as the water cycle.

So as ages pass, salt and other elements pile up, making the seas more and more salty. The salt concentration is not equal throughout. The poles are fresher because of continuous melting, and the equator is saltier, due to constant evaporation.

                       But to us it always tastes the same, like salty water.

Resources and related reads:

UT Dallas: Why is the sea salty?

Palomar College: Why is the ocean salty?

BBC: Why is the sea so salty?

Wonderopolis: Why is the sea salty?

Why don't we see stars in the city?

It’s night, it’s dark, and the moon is out. You walk out onto the balcony, or the street, or even the local park, look up and there’s nothing. Perhaps Venus’ bright dot, and a few other prominent celestial lights, but beyond that a dark, grey velvet hangs above you.

Maybe you’ve been in the countryside once, or maybe you’ve never left the city, but you’ve seen plenty of programmes, and pictures and books to know something isn’t right. That a veil lies between you and the sky because the millions of sparkly dots we call stars are missing.

A sad existence under a starless sky, making you question where did the nightlights go? Why can’t we see them hanging above the tall buildings of our cities?

Star visibility depends on weather conditions, air humidity and geographical location, with more stars visible in dry deserts and less in warm, wet equatorial tropics.

But the biggest impediment is pollution. Not car exhausts and smog, not too much anyway, but light pollution.

Modern metropolises are lit with blinding lights. You can’t find a single street or building, not one you’d like to wander into anyway, that isn’t illuminated 24/7. Windows, streetlamps, billboards, all project their light into the sky, often needlessly and with great electric costs, obscuring the fainter starlight. But it is the price of civilization. Even if it affects wildlife and takes away our stars.

With all this light on the ground, is it any surprise the sky remains vacant?

So if you wish to stargaze, you may always find a nice cottage in the countryside, far away from the big city, and enjoy a few nights under a starlit sky.

But not all is lost for city dwellers as new policies, technologies and designs are being implemented to combat light pollutions. In many cities streetlamps are redesigned to point downwards and limit the light projected at the sky. They are also fainter, still enough to see, while limiting power consumptions. Additional laws are being passed to limit night light use in big cities. And finally, everyone can make their personal contribution by turning off inessential lighting whenever possible.

And one day, we may yet see the stars and even the milky way again above our cities.

References and related reads:

National Geographic: Light Pollution

Planet Patrol: Light Pollution

CNN: Who turned off the stars?

Gizmodo: How cities would look without lights.