Category Archives: Science

Why do colors fade in the sun?

Unless you’re a hermit, you’ve experienced the strength of the sun many times in life. It doesn’t even require long days at the beach or afternoons spent at outdoor events. Just standing outside on a bright, sunny day provides a glimpse of its power. The evidence is in the sweat that trickles and the red tone that rises on your bare arms, legs or face. In fact, our bodies are the sun’s best way to boast.

Whenever you spend a little too much time outside with exposed skin, you can count on some amount of sunburn. Sunburn is the result of overexposure to the sun’s ultraviolet radiation. It causes chemical changes in the skin, leading to alterations in color, among other physical changes.

For many, the reward of sun exposure is a nice tan. However, due to the chemical changes taking place, this can come at a price: overexposure damages the DNA, sometimes even causing skin cancer. In other words, there are risks and rewards when we spend time in the sun.

But what about for nonliving things?

Humans aren’t unique in their susceptibility to sun damage. Along with living creatures, inanimate objects undergo changes after sun exposure. And such changes include alterations in color.

One key ingredient: ultraviolet radiation

The sun is the primary source of ultraviolet radiation, a type of electromagnetic radiation that is present in sunlight. It is named as such because UV light is beyond the visible spectrum of light, which ends with violet, the highest frequency of visible light. Thus, “ultra”-violet.

There are three main types of ultraviolet light: UVA, UVB and UVC.

Name Wavelength (nm) Absorbed by Ozone?
UVA 315-400 Little effect
UVB 280-315 Most absorbed
UVC 100-280 All absorbed

At the top of Earth’s atmosphere, right on the edge of space, 10% of sunlight is made up of these types of UV light. By the time sunlight hits the ground, it is only 3% UV light, and of this light, over 95% is UVA, the rest UVB. This small amount of UV light is strong enough to cause cancer with overexposure; however, the intensity is not uniform.

According to the American Cancer Society, several factors impact the strength of rays when they hit the earth:

  • Time of day: UV rays are strongest between 10 am and 4 pm.

  • Season of the year: UV rays are stronger during spring and summer months. This is less of a factor near the equator.

  • Distance from the equator (latitude): UV exposure goes down as you get further from the equator.

  • Altitude: More UV rays reach the ground at higher elevations.

  • Cloud cover: The effect of clouds can vary. Sometimes cloud cover blocks some UV from the sun and lowers UV exposure, while some types of clouds can reflect UV and can increase UV exposure. What is important to know is that UV rays can get through, even on a cloudy day.

  • Reflection off surfaces: UV rays can bounce off surfaces like water, sand, snow, pavement, or grass, leading to an increase in UV exposure.

There are also factors that influence the amount of UV exposure a person receives, such as length of time exposed and type of protection (clothing, sunscreen).

When each of the above are combined, they affect how the sun changes the color of inanimate objects we see.

So how do we see color?

 

How the eye works

The human eye uses three cell types in the retina to distinguish color. Called cones, each cell type is most sensitive to a different wavelength of light: short wavelength, medium wavelength and long wavelength. Short cones can detect light wavelengths in the range of 400 to 500 nm, medium cones 450 to 630 nm and large cones 500 to 700 nm. These each cover a different, often overlapping segment of the range of visible light, and when stimulated, the cones send signals to your brain to process color.

Single or multiple cones may show high stimulation when exposed to visible light, but it all depends on the particular wavelength. For instance, a short cone may react sharply to 450 nm wavelengths while the same light barely registers with medium cones. At the same time, each cone type has individual peak sensitivity (i.e., a strongest reaction) to specific wavelengths, and the overlap in detectible ranges allows two cones to react with the same strength to the same wavelength. For example, both the medium and long cones may respond equally as strong to wavelengths of 575 nm, even though they each react most strongly to other wavelengths. Combined with current knowledge, these facts help complicate what we thought we knew about sight.

light spectrum - cone fundamentals
Courtesy Wikimedia Commons

If you’re like me, you’re probably most familiar with previous thoughts on sight, where scientists believed that short, medium, and long cones corresponded to the colors blue, green, and red, respectively. However, we now know that cones do not correspond to specific color detection, and that they each detect other colors as well. Interestingly, peak sensitivity in each cone can differ from person to person, even among those with normal color vision. In other words, your short cones may react most strongly to a 425 nm wavelength, whereas mine react most strongly to 440nm, both of which are different hues!

How objects show their color

Despite changes in our thinking about vision, one thing is still certain: while each person’s cones may react differently to the same wavelength, all of our cones need to detect reflected light for us to distinguish color. For example, imagine you an apple. The red color you see is based on the wavelengths that are bouncing off, rather than being absorbed, by the fruit. In other words, the apple skin doesn’t have red in it; it is reflecting the color red as light bounces off of it, due to chemicals in the peal.

I know what you’re thinking. Black and white seem different, but the same principle applies.

black and whiteWe see white when all of the colors are reflected. This is why the sun at noon looks white: all of the colors are reaching the eye. But why does it look yellow, orange or red at other times of the day? As the sun’s position changes in the sky, shorter wavelengths, such as blues and greens, get scattered in the atmosphere, leaving longer wavelengths, the reds and oranges, to reach your eye.

Black, on the other hand, is the lack of color. When you look at a black object, like a shiny new tire or the outer frame of your TV, there is no light reflected out because it is all absorbed by the object. And when there are no reflected wavelengths, there is no color.

Putting it all together: it’s in the chemistry

Although not the only possible culprit, UV radiation plays a significant part in the breakdown of the colors we see in outdoor objects. Unlike skin, an inanimate object doesn’t have DNA to destroy, but it is made of chemicals that can degrade. These chemicals, such as dyes, are subject to the same factors that cause sunburn, and thus the strength of UV light and the amount of exposure objects receive cause chemical changes that alter, among other things, color.

Remember the apple skin mentioned before? The chemicals in its skin do not allow the absorption of certain wavelengths, instead reflecting them.  When it comes to objects such as an outdoor table umbrella, the same idea applies.

blue and white umbrellaIf you consistently leave a blue umbrella outdoors, the compounds and molecules that reflect blue wavelengths will be exposed to varying strengths of UV light, depending on the weather, location, proximity to reflective surfaces, etc. Over time, the energy from the constant battering of UV light wears down the chemical bonds between the molecules, eventually breaking them and leading to gradual fading. This is called photodegradation.

In other words, the color fades because the molecular bonds changed and the object can no longer absorb and/or reflect certain wavelengths on the visible spectrum.  Objects may even eventually turn completely white because the wavelengths reflected have changed to that beyond our visible spectrum.

So then why do we get darker in the sun?

One thing we have that objects don’t is melanocytes. These cells exist in the lower layer of the epidermis, and when UVA rays are absorbed into the skin, they activate the melanocytes, which then produce melanin, the skin’s natural protector.

Melanin is a pigment that darkens the skin beyond your natural skin tone to protect from the harmful effects of sunlight. It absorbs light and disperses UV radiation, but as anyone whose tan has faded knows, the effect is only temporary. Every 28-30 days, the newly darkened cells make their way up to the surface and are shed, just like all skin cells.

Is there any way to protect the color of outdoor objects?

It’s not likely that you can completely prevent color fading from sunlight exposure, but you may be able to slow it by making careful choices. For instance, some dyes and other chemicals are stronger against UV; since red dyes appear to fade most quickly, it may be best to avoid the color. There are also spray-on chemicals available that claim to block UV and prevent fading.

VIDEO: Learning the facts on ocean pollution

Although we see pollution on our beaches, sidewalks and streets, it’s not often that we think about what we don’t see–the pollution that winds up floating in and resting on the bottom of our oceans.

Put the following videos on your watch list to see what’s going on in our oceans and why it’s important that we recognize it, and hopefully make changes to slow it. Who knows? Perhaps with the help of technology, we can even clean it up.

How did the deepest part of the ocean get so polluted?

How much plastic is in the ocean?

The Great Pacific Garbage patch explained

How pollution is changing our ocean’s chemistry

Turning down the volume on human noise pollution for marine life

Can this project clean up millions of tons of ocean plastic?

How do they do it?: Sense and adaptation in plants

You’ll never teach your house plants to do tricks like your dog. They’ll never answer “what’s wrong?” when looking puny. But you see them close their petals a night. Venus fly traps snap shut on their prey. Studies show they even respond to music! So, what gives?

Although your household fern lacks the animal-like brain we’re used to, that doesn’t mean it’s senseless. In fact, plants are keenly aware of their surroundings. Through proprioception; specific cells, genes and hormones; the familiar circadian rhythm and other specializations, plants can sense and adapt to their environment.

Proprioception: it’s not just for animals!

Just like humans have unconscious body awareness, plants sense themselves and their spatial orientation. Humans have this ability due to muscle spindles in the muscles and tendons, whereas plants use their own distinct cells to trigger gravitropism, or growth in response to gravity. In other words, gravity tells plants where to direct their roots and their shoots.

root rot in cicer arietinum
By Bjornwireen (Own work) CC BY-SA 3.0 or GFDL via Wikimedia Commons

According to ScienceDaily, there is controversy over the chemical changes that promote the proper orientation of root growth:

To date, gravity sensing in plants has been explained by the starch-statolith hypothesis. For example, in roots, gravity-sensing cells at the tip of the root contain dense, starch-filled organelles known as amyloplasts. Amyloplasts settle to the bottom of the cells in response to gravity, which then triggers the hormone auxin to move to another, distinct, area of cells and causes them to elongate and bend toward gravity. However, the molecular details of exactly how the physical movement and settling of amyloplasts in one set of cells triggers the accumulation of auxin in another, physically distant, set of cells in a plant remains a mystery.

The most prevalent current hypothesis is that the cytoskeleton, or cellular scaffolding, plays a major role in this gravity-sensing, intercellular communication; the cytoskeleton is made up of filaments, consisting of the proteins actin or tubulin, that allow movement of materials along strands, such as is seen in meiosis or mitosis. However, there is a major controversy in the field regarding the role of actin in gravitropism primarily due to contradictory outcomes in studies where actin was inhibited — the most interesting ones, according to Blancaflor, being those where actin disruption actually led to enhanced gravitropism.

So, how do they do it? One thing is sure: There are specific gravity-sensing cells that tell the plant, ‘Hey! This way is down!’

blue flowerAbout face! The sun’s the other way!

At a young age, we learn that photosynthesis is the method plants use to make their own food. Using sunlight, water and carbon dioxide, plants synthesize glucose, which is the fuel that keeps their chemical processes going.

But what if they’re not getting enough sunlight? They’ll sense it and take action, triggering phototropism.

Defined as the orientation of an organism toward light, phototropism sends chemical signals the stem, telling it to bend. From the tip of the stem, D6PK protein kinase signals the release of the phytohormone auxin. D6PK signals to PINs, or export proteins, which guide auxin from cell to cell, and eventually to its destination. This triggers cells to elongate, causing the plant to bend in the appropriate direction to receive more light.

Growth of plants isn’t only dependent on light and gravity, however.

DYK? Plants sense temperature changes

thermometer sunA 2016 study published in Science showed that phytochrome B, a photoreceptor, responded not only to changes in light but also changes in temperature.

Under varying light and temperature conditions, the scientists grew Arabidopsis seedlings and studied how the differences affected growth. The results showed that even with plenty of light, higher temperatures caused phytochrome B to inactivate, which in turn led to a spurt of growth. Researchers thought the opposite would happen, but instead, the plants reacted as if they needed more sunlight.

Such a surprising outcome supports the hypothesis that phytochrome B is also a temperature sensor.

They can’t ‘talk,’ but plants can communicate!

You’ve smelled the skunk’s defense mechanism. Read of the poison dart frog’s deadly, toxic armor.  Heard monkeys going ape to warn of a predator. But did you know plants warn of danger, too?

Volatile organic compounds are the plant’s communication system. These airborne, odorous chemicals warn neighboring plants about dangers such as plant-eating insects. Other plants sense these chemicals, in turn releasing their own to ward off the incoming threat, whatever it may be. But airborne signals aren’t the only method.

beetle plantA 2009 study from the University of Aberdeen in Scotland showed that plants can send messages through other organisms, such as fungi:

Five weeks earlier, Babikova filled eight 30 cm–diameter pots with soil containing Glomus intraradices, a mycorrhizal fungus that connects the roots of plants with its hyphae, the branching filaments that make up the fungal mycelium. Like a subterranean swap meet, these hyphal networks facilitate the trade of nutrients between fungi and plants. In each pot, Babikova planted five broad bean plants: a “donor” plant surrounded by four “receiver” plants. One of the receivers was allowed to form root and mycorrhizal contact with the donor; another formed mycorrhizal contact only, and two more had neither root nor mycorrhizal contact. Once the mycorrhizal networks were well established, Babikova infested the donor plants with aphids and sealed each plant in a separate plastic bag that allowed for the passage of carbon dioxide, water, and water vapor but blocked larger molecules, such as the VOCs used for airborne communication.

Four days later, Babikova placed individual aphids or parasitoid wasps in spherical choice chambers to see how they reacted to the VOC bouquets collected from receiver plants. Sure enough, only plants that had mycorrhizal connections to the infested plant were repellent to aphids and attractive to wasps, an indication that the plants were in fact using their fungal symbionts to send warnings.

Not only can plants warn of attacks from herbivores and pathogens, but they can also warn of drought and adapt to information received from plants around them.

What else can plants sense?

Check out the video below to find out!

Happy 4th of July! 7 scientific and technological events on this day in history

President Roosevelt sends first worldwide message via cable

On July 4, 1903, FDR sent the first message to ever travel around the globe via the Pacific Cable, wishing "a happy Independence Day to the US, its territories and properties..." It took 9 minutes to reach the entire world.

Mars Pathfinder lands a rover on Mars

On Independence Day in 1997, the Mars Pathfinder spacecraft landed on Mars, bringing with it a base station and the Sojourner rover. Lasting almost three months, Pathfinder transmitted 16,500 pictures and 8.5 million measurements from the surface of Mars.

Vermont hits record high

Back in 1911, the 4th of July saw a new record high in Vernon, Vermont. The temperature hit 105 degrees! 

Maryland sees record rainfall

A downpour on July 4, 1956, caused Unionville, Maryland, to gain a record it keeps today: most rainfall in one minute.
A whopping 1.22 inches fell! 

Explorer 38 (aka RAE 1) is launched

Following its Independence Day launch from Vandenberg Air Force Base, Explorer 38 went on to measure celestial radio sources. According to NASA, "the RAE-1 spacecraft measured the intensity of celestial radio sources, particularly the sun, as a function of time, direction, and frequency (0.2 to 20 MHz)."

Hotmail email goes live

Now branded as Outlook, the free email service Hotmail (first stylized as HoTMaiL, as in HTML) launched on July 4, 1996.

 NASA collides spacecraft with comet, for science

On July 3, 2005, NASA's Deep Impact spacecraft released an impactor, a self-propelled craft that moves to collide with the comet. The impactor took photos near the comet's surface right before impact with the surface on July 4th. From this experiment, scientists discovered ice, dust, and carbon-containing materials on the surface of Tempel 1, the comet in question.

Anti-GMO? This modified corn could save lives!

University of Arizona plant geneticist Monica Schmidt has genetically modified corn plants to turn off the ability of Aspergillus species of fungus to spread a toxin that leads to multiple life-altering and deadly conditions, which could be a game-changer for developing countries all over the world.

The procedure is called host-induced gene silencing (HIGS), and it involves inserting foreign genetic material into a host species so that the host can silence unwanted genes expressed by pathogens and pests. Schmidt and colleagues inserted RNA from the aspergillus fungus into the corn plant’s genetic code. When the fungus tried to infect the corn plant, the two exchanged genetic code, which, since the corn contained aspergillus genes, shut down the ability of the fungus to produce aflatoxin.

The trials were 100 percent effective according the peer-reviewed results published in Science Advances journal, and there were no other changes to the corn’s genetic code. The success of this initial trial is important because Aspergillus species cause illness, death, and economic loss in places where the fungi are rampant.

What is Aspergillus and why is its toxin dangerous?

Aspergillus refers to a genus of fungi that includes a few hundred species. Aspergillus flavus and Aspergillus parasiticus are the main species that produce dangerous aflatoxins, a certain fungus that can contaminate crops at all stages, from development to processing. These fungi are found on crops such as coffee, cocoa, copra, corn, cottonseed, groundnuts, peanuts, tree nuts, and yam chips, especially in warm, humid regions.

Exposure to aflatoxins can lead to liver disease, liver failure, liver cancer, aflatoxin toxicity leading to death, Reye’s syndrome, and impaired growth in children. According to the Partnership for Aflatoxin Control in Africa, studies have also linked the toxins “to immune suppression, increased susceptibility to diseases such as HIV and malaria, and a possible reduction in the effectiveness of vaccines.”

corn

Who does this impact?

These problems are especially important in developing countries. For instance, the Centers for Disease Control and Prevention states that Kenya suffers from high rates of aflatoxin contamination and poisoning, with up to 40% of cases resulting in death. This is because testing is not readily available in these countries, resulting in undetected contamination. Aflatoxins have an impact on the economy and nutrition in countries without widespread testing available because 1) contaminated crops must be destroyed, 2) the crops do not meet standards for trade, and 3) aflatoxins can cause illness and decreased yields in livestock.

What’s next?

According to the Arizona Daily Star, Schmidt is seeking funding for phase two trials but has hit roadblocks because of the public distrust of GMOs.

The Bill and Melinda Gates Foundation funded her initial research but refused to fund the second leg of the trial, stating that they were funding other ways to fight aflatoxins, reports the Arizona Daily Star. They also turned down her next project involving fighting the fungus itself, but the US Department of Agriculture agreed to fund that research.

Right now phase two is still unfunded, which is unfortunate because if a group would overcome the GMO stigma and provide a grant to Schmidt and her colleagues, the eventual approval and release of such genetically modified corn could save lives in Africa.