CLOSE
Original image
ThinkStock

Why Do We Tan?

Original image
ThinkStock

Sit out in the sun too long and ultraviolet radiation from sunlight penetrates your skin and cells, damaging their RNA and DNA. This is bad news, as DNA provides our bodies with all the genetic instructions they need to develop, survive and go about their business, and this kind of DNA damage can lead to skin cancer. To protect you from this, your body helpfully tans, darkening the the skin with a pigment called melanin that reduces UV penetration into cells.

UV radiation stimulates the darkening of existing melanin and spurs increased melanogenesis, the production of new melanin. Cells called melanocytes generate the pigment and push it out of the cell, where it darkens the skin and absorbs and transforms absorbed UV energy into heat.

Melanogenesis results in a delayed tan that only becomes visible several hours after UV exposure and lasts longer than the tanning caused by darkening of existing melanin. Over time, a tan fades as darkened skin layers are pushed upward by new cells with less melanin, and are eventually scaled off.

Why do we get sunburn?

While we might say someone with sunburn was out “baking” too long or got “fried,” sunburns are different from the burn one might get from, say, touching a hot stove. That’s a thermal burn caused by the heat of the stove. While the sun does give off heat, a sunburn is caused by ultraviolet-B radiation.

When someone’s exposure to UV radiation exceeds their body’s ability to protect the skin with tanning, the radiation  causes damage to DNA, like we talked about above. This prompts the body to try and fix things. Bloodflow to the capillary bed of the dermis (the second outermost layer of skin) increases so cells can repair the damage, which results in warmth and redness of the skin. Inflammatory immune cells also flock to the damaged tissue, causing us to perceive pain and, hopefully, consider staying out of the sun for a while. Eventually, the damaged skin cells die, and the burned skin starts to peel.

Original image
iStock
arrow
Big Questions
How Does Autopilot Work on an Airplane?
Original image
iStock

How does autopilot work on an airplane?

Joe Shelton:

David Micklewhyte’s answer is a good one. There are essentially a few types of features that different autopilots have. Some autopilots only have some of these features, while the more powerful autopilots do it all.

  • Heading Hold: There’s a small indicator that the pilot can set on the desired heading and the airplane will fly that heading. This feature doesn’t take the need for wind correction to desired routing into account; that’s left to the pilot.
  • Heading and Navigation: In addition to holding a heading, this version will take an electronic navigation input (e.g. GPS or VOR) and will follow (fly) that navigation reference. It’s sort of like an automated car in that it follows the navigator’s input and the pilot monitors.
  • Altitude Hold: Again, in addition to the above, a desired altitude can be set and the aircraft will fly at that altitude. Some autopilots have the capability for the pilot to select a desired altitude and a climb or descent rate and the aircraft will automatically climb or descend to that altitude and then hold the altitude.
  • Instrument Approaches: Autopilots with this capability will fly preprogrammed instrument approaches to the point where the pilot either takes control and lands or has the autopilot execute a missed approach.

The autopilot is a powerful computer that takes input from either the pilot or a navigation device and essentially does what it is told to do. GPS navigators, for example, can have a full flight plan entered from departure to destination, and the autopilot will follow the navigator’s guidance.

These are the majority of the controls on the autopilot installed in my airplane:

HDG Knob = Heading knob (Used to set the desired heading)

AP = Autopilot (Pressing this turns the autopilot on)

FD = Flight Director (A form of navigational display that the pilot uses)

HDG = Heading (Tells the autopilot to fly the heading set by the Heading Knob)

NAV = Tells the autopilot to follow the input from the selected navigator

APR = Tells the autopilot to fly the chosen approach

ALT = Tells the autopilot to manage the altitude, controlled by the following:

VS = Vertical Speed (Tells the autopilot to climb or descend at the chosen rate)

Nose UP / Nose DN = Sets the climb/descent rate in feet per minute

FLC = Flight Level Change (An easy manual way to set the autopilot)

ALT Knob = Used to enter the desired altitude

This post originally appeared on Quora. Click here to view.

Original image
iStock
arrow
Big Questions
What's the Difference Between Vanilla and French Vanilla Ice Cream?
Original image
iStock

While you’re browsing the ice cream aisle, you may find yourself wondering, “What’s so French about French vanilla?” The name may sound a little fancier than just plain ol’ “vanilla,” but it has nothing to do with the origin of the vanilla itself. (Vanilla is a tropical plant that grows near the equator.)

The difference comes down to eggs, as The Kitchn explains. You may have already noticed that French vanilla ice cream tends to have a slightly yellow coloring, while plain vanilla ice cream is more white. That’s because the base of French vanilla ice cream has egg yolks added to it.

The eggs give French vanilla ice cream both a smoother consistency and that subtle yellow color. The taste is a little richer and a little more complex than a regular vanilla, which is made with just milk and cream and is sometimes called “Philadelphia-style vanilla” ice cream.

In an interview with NPR’s All Things Considered in 2010—when Baskin-Robbins decided to eliminate French Vanilla from its ice cream lineup—ice cream industry consultant Bruce Tharp noted that French vanilla ice cream may date back to at least colonial times, when Thomas Jefferson and George Washington both used ice cream recipes that included egg yolks.

Jefferson likely acquired his taste for ice cream during the time he spent in France, and served it to his White House guests several times. His family’s ice cream recipe—which calls for six egg yolks per quart of cream—seems to have originated with his French butler.

But everyone already knew to trust the French with their dairy products, right?

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios