Siberian Hamster Testicles are Growing, Which Means the Vernal Equinox is Here

Standing before the Pyramid of the Sun in Teotihuacan, Mexico, a woman embraces spring on the vernal equinox. Image Credit: Ronaldo Schemidt/AFP/Getty Images

Today you, I, and everyone in the world have something in common. Regardless of whether you live in Australia or Austria or Austin, day and night are approximately the same length the whole world over. Today is the vernal equinox—the first day of spring. If you live in the Northern Hemisphere, your days will be getting longer, your trees greener, and your animals friskier. We think it all happens because billions of years ago, a proto-planet collided with an embryonic Earth. Here's what's going on.


Winter and summer have nothing to do with the distance of the Earth from the Sun. Rather, seasons are the product of axial tilt and orbital dynamics. The Earth is tilted slightly at 23.5 degrees relative to its orbital plane. (That tilt is thought related to the aforementioned collision.) The orientation of the tilt never changes, and as Earth revolves around the Sun over the course of a year, different latitudes are thus in direct sunlight. When the Northern Hemisphere is in direct sun, it is summertime there and wintertime down under, and vice versa when the Southern Hemisphere is in direct sunlight.

If this is hard to visualize, take your cell phone and hold it upright next to the left side of your computer screen, tilted slightly toward the computer. The top-right corner should be closest to the screen. It is summertime in that corner (the screen being the Sun in this demonstration). Now keep everything the same, but bring your phone to the right side of your screen. Now the bottom-left of your phone is closer. It is summertime there. If your phone were a spinning sphere, those two corners would be the Tropics of Cancer and Capricorn, respectively. Over a full orbit of the Earth around the Sun, this means the center of the Earth—the Equator—is in direct sunlight twice.

Today is one of those times, marking the transition from winter to spring in the Northern Hemisphere. (The other, autumnal equinox, transitions fall to winter.)


Humans today have it pretty easy. We have coats and fires during the winter, and shorts, air conditioning, and Disney vacations in the summer. For many in the developed world, seasons are in some ways a neat way of marking time, but they don’t necessarily dictate the course of our lives. For plants and animals, though, the seasons are serious business. The availability of food and warmth are vital for reproduction and rearing young animals. During the fall and short winter days, for example, the testicles of Siberian hamsters change dramatically in size (and under no circumstances should you google that). That’s a pretty granular-level effect of the axial tilt of an entire planet.

The same goes for birds flying south for the winter. Studies suggest that the migration is in large measure simply birds following the food. (Starvation winters in the north can be summer feasts in the south. Go where the worms are.) There is some evidence that the migratory patterns are also wired into the DNA of some birds. We’ve discussed this previously at mental_floss:

Captive birds have been observed getting pretty fidgety and changing their sleep patterns right before their natural migration time. Ethologists—those who study animal behavior—call the birds' behavior zugunruhe ("migratory restlessness"). Captive birds display zugunruhe even if they're not exposed to natural light or to seasonal temperature changes.

It goes far beyond that, though. Even plants know what’s up. “Spring is sooner recognized by plants than by men,” says the Chinese proverb. Plants produce phytochromes, which are compounds sensitive to the light spectrum and used to regulate flowering and budding. In some regions, the vernal equinox and the longer days of direct sunlight it brings lead to an increased production of red phytochromes. (In the winter, the Sun’s position in the sky, and the sunlight often shining indirectly, leads to the increased production of far-red phytochromes.) As the ratios shift, you get flowering. No tilt, no bouquets.

So while today is an interesting day to mark for social reasons—a rare point of global harmony and equality imposed by the natural world, even if only concerning light and dark—it’s also a day marking a shift in the behaviors of the natural world itself. Today we are all equal, and for the next few months, the Northern Hemisphere begins anew.

Here's What Actually Happens When You're Electrocuted

Benjamin Franklin was a genius, but not so smart when it came to safely handling electricity, according to legend. As SciShow explains in its latest video, varying degrees of electric current passing through the body can result in burns, seizures, cessation of breathing, and even a stopped heart. Our skin is pretty good at resisting electric current, but its protective properties are diminished when it gets wet—so if Franklin actually conducted his famous kite-and-key experiment in the pouring rain, he was essentially flirting with death.

That's right, death: Had Franklin actually been electrocuted, he wouldn't have had only sparks radiating from his body and fried hair. The difference between experiencing an electric shock and an electrocution depends on the amount of current involved, the voltage (the difference in the electrical potential that's driving the current), and your body's resistance to the current. Once the line is crossed, the fallout isn't pretty, which you can thankfully learn about secondhand by watching the video below.

Big Questions
Does Einstein's Theory of Relativity Imply That Interstellar Space Travel is Impossible?

Does Einstein's theory of relativity imply that interstellar space travel is impossible?

Paul Mainwood:

The opposite. It makes interstellar travel possible—or at least possible within human lifetimes.

The reason is acceleration. Humans are fairly puny creatures, and we can’t stand much acceleration. Impose much more than 1 g of acceleration onto a human for an extended period of time, and we will experience all kinds of health problems. (Impose much more than 10 g and these health problems will include immediate unconsciousness and a rapid death.)

To travel anywhere significant, we need to accelerate up to your travel speed, and then decelerate again at the other end. If we’re limited to, say, 1.5 g for extended periods, then in a non-relativistic, Newtonian world, this gives us a major problem: Everyone’s going to die before we get there. The only way of getting the time down is to apply stronger accelerations, so we need to send robots, or at least something much tougher than we delicate bags of mostly water.

But relativity helps a lot. As soon as we get anywhere near the speed of light, then the local time on the spaceship dilates, and we can get to places in much less (spaceship) time than it would take in a Newtonian universe. (Or, looking at it from the point of view of someone on the spaceship: they will see the distances contract as they accelerate up to near light-speed—the effect is the same, they will get there quicker.)

Here’s a quick table I knocked together on the assumption that we can’t accelerate any faster than 1.5 g. We accelerate up at that rate for half the journey, and then decelerate at the same rate in the second half to stop just beside wherever we are visiting.

You can see that to get to destinations much beyond 50 light years away, we are receiving massive advantages from relativity. And beyond 1000 light years, it’s only thanks to relativistic effects that we’re getting there within a human lifetime.

Indeed, if we continue the table, we’ll find that we can get across the entire visible universe (47 billion light-years or so) within a human lifetime (28 years or so) by exploiting relativistic effects.

So, by using relativity, it seems we can get anywhere we like!

Well ... not quite.

Two problems.

First, the effect is only available to the travelers. The Earth times will be much much longer. (Rough rule to obtain the Earth-time for a return journey [is to] double the number of light years in the table and add 0.25 to get the time in years). So if they return, they will find many thousand years have elapsed on earth: their families will live and die without them. So, even we did send explorers, we on Earth would never find out what they had discovered. Though perhaps for some explorers, even this would be a positive: “Take a trip to Betelgeuse! For only an 18 year round-trip, you get an interstellar adventure and a bonus: time-travel to 1300 years in the Earth’s future!”

Second, a more immediate and practical problem: The amount of energy it takes to accelerate something up to the relativistic speeds we are using here is—quite literally—astronomical. Taking the journey to the Crab Nebula as an example, we’d need to provide about 7 x 1020 J of kinetic energy per kilogram of spaceship to get up to the top speed we’re using.

That is a lot. But it’s available: the Sun puts out 3X1026 W, so in theory, you’d only need a few seconds of Solar output (plus a Dyson Sphere) to collect enough energy to get a reasonably sized ship up to that speed. This also assumes you can transfer this energy to the ship without increasing its mass: e.g., via a laser anchored to a large planet or star; if our ship needs to carry its chemical or matter/anti-matter fuel and accelerate that too, then you run into the “tyranny of the rocket equation” and we’re lost. Many orders of magnitude more fuel will be needed.

But I’m just going to airily treat all that as an engineering issue (albeit one far beyond anything we can attack with currently imaginable technology). Assuming we can get our spaceships up to those speeds, we can see how relativity helps interstellar travel. Counter-intuitive, but true.

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


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