How Do Astronauts Reenter Earth's Atmosphere Without Burning Up?

iStock
iStock

Robert Frost:

Currently, astronauts and cosmonauts return to Earth in a Soyuz capsule. The Soyuz capsule has a curved ablative heat shield that is used to prevent heat from building up and penetrating the crew cabin.

As the capsule plummets through the atmosphere it slams into molecules of air. These bounce off of the capsule and in turn slam into the air molecules that were behind them. This creates a shockwave in front of the vehicle. The greatest temperature is at the shockwave, so forming the shockwave farther from the vehicle surface reduces the amount of heating the vehicle experiences. This displacement is related to the shape of the capsule and explains the curvature.

Some heat still makes it to the vehicle surface, and that’s where the ablative heat shield comes into play. As the outer molecules of the heat shield absorb heat, they reach a point where they vaporize and leave the surface of the vehicle. When they do this, they carry away the heat they have absorbed. This phenomenon is called pyrolysis. The next layer then gets hotter and hotter until it vaporizes and takes its heat away. Eventually, the vehicle has slowed to the point where heat is no longer significant and what is left of the outer surface will be relatively cool.

So, the idea is to create a heat shield that has the right curvature, ablative properties, and thickness such that significant heat never makes it to the crew compartment or vital equipment.

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

Why Do Dogs Lick?

iStock/MichaelSvoboda
iStock/MichaelSvoboda

​One of the more slightly annoying things our dogs do (or most adorable, depending on who you ask) involves their tongue obsessively licking every crevice of every spot possible in pretty much the whole world. From our faces to our furniture to themselves, some dogs are absolutely in love with licking anything and everything. Although it can be cute at first, it quickly gets pretty gross. So why do they do it?

According to ​Vetstreet, your pup's incessant licking is mostly their way of trying to show affection. When we pick up our dogs or give them attention, chances are we kiss or pat their heads, along with petting their fur. Their way to show love back to us is by licking.

However, there are other reasons your dog might be obsessively licking—including as a way to get attention. Licking can be a learned behavior for dogs, as they see that when they lick their owner, they get more attention. The behavior can seem like something humans want which, to an extent, it is.

Licking is also a sensory tool, so if your dog is licking random objects or areas of your home, they're probably just exploring. It's easier to get a feel for their surroundings if they can taste everything. But licking objects like your rug or furniture can also be indicative of anxiety or boredom (which can often lead to destructive behavior), and a recent study linked excessive licking of surfaces to certain gastrointestinal disorders.

Another reason for licking is your dog wanting to clean themselves and/or spots around them. They've seen it since they were born; animals lick things ritualistically for cleaning and care. If your dog seems to be obsessed with licking themselves or one particular thing, they probably are. (Yes, dogs can have OCD, too.)

As Vetstreet points out, "excessive" dog licking often only seems excessive to the dog's owner, not the pooch itself. But if it's bothersome enough to you, a trainer can often help curb your dog's enthusiasm for giving wet, sloppy kisses. And while strange behavior is not rare for pets, if your dog's licking seems odd or in any way concerning, there's no harm in taking your pet to the vet to check it out—even if it's just for peace of mind.

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How Are Balloons Chosen for the Macy's Thanksgiving Day Parade?

iStock/RoBeDeRo
iStock/RoBeDeRo

The balloons for this year's Macy’s Thanksgiving Day Parade range from the classics like Charlie Brown to more modern characters who have debuted in the past few years, including The Elf On The Shelf. New to the parade this year are the Teenage Mutant Ninja Turtles. But how does the retail giant choose which characters will appear in the lineup?

Balloon characters are chosen in different ways. For example, in 2011, Macy’s requested B. Boy after parade organizers saw the Tim Burton retrospective at the Museum of Modern Art. (The company had been adding a series of art balloons to the parade lineup since 2005, which it called the Blue Sky Gallery.) When it comes to commercial balloons, though, it appears to be all about the Benjamins.

First-time balloons cost at least $190,000—this covers admission into the parade and the cost of balloon construction. After the initial year, companies can expect to pay Macy’s about $90,000 to get a character into the parade lineup. If you consider that the balloons are out for only an hour or so, that’s about $1500 a minute.

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