The Science Behind Life Below the Equator

Today I'm going to get a little nerdy on you guys. Ok, really nerdy. What can I say? My dad is a retired earth science professor. I come by it honestly.

These days I'm not just far from where I grew up—I'm living in a completely different hemisphere! To be exact, my adopted home of Necochea has a latitude of 38° 33' S, as compared to Philadelphia's latitude of 39° 57' N. Though the two locations are virtually the same distance from the equator, living south of that imaginary line makes all the difference, with profound implications ranging from what the sky looks like at night to animal migration patterns. 

Let's take a look at four aspects of the natural world that differ in the southern hemisphere. I've done my best to provide you with reputable scientific sources about each phenomenon so you can indulge your inner nerd and explore further if you so choose.

Reversal of the Seasons

The seasons are reversed in the northern and southern hemispheres; when it is winter in the northern hemisphere, it is summer in the southern hemisphere, and vice versa. The fine folks at the Lunar and Planetary Institute in Houston, TX have written up a very clear explanation of the causes of this phenomenon, so rather than reinvent the wheel, I'm going to direct you here to read all about it.

Misplaced Snowman by puroticorico, on Flickr [Creative Commons]

Opposing seasons turn things topsy-turvy when it comes to holidays. For example, most of the classic symbols of Christmas and Easter are strongly linked to the northern hemisphere seasons in which they're celebrated. While you're all dreaming of a white Christmas, we're seriously thinking about heading to the beach to escape the heat (though this is also true for those of you living in the tropics).

The influence of the reversal of seasons extends to the academic calendar as well. In Argentina, the school year gets underway in March and finishes up in December, with students enjoying an extended summer break just like their counterparts in the northern hemisphere.

The Coriolis Effect

If you ask someone to describe the Coriolis effect, his response (if it's not a blank stare) will be something like this: "The Earth's rotation causes the water in a sink or toilet to drain in one direction in the northern hemisphere and in the opposite direction in the southern hemisphere." If you need to brush up on your physics, the University Corporation for Atmospheric Research offers an accurate description of the Coriolis effect.

I hate to be the bearer of bad news, but the Coriolis effect does not influence the direction that water drains in a sink or toilet. The professors at Penn State University want you to know that although in theory water should drain in opposite directions in the two hemispheres, in practice it is very difficult to demonstrate this phenomenon due to differences in toilet and sink design that easily overcome the relatively weak Coriolis force. 

The Coriolis Effect by Digit_AL, on Flickr

While you're unlikely to catch the Coriolis effect at work while staring into the toilet, you may have better luck if you flip to the Weather Channel. "The rotation of the Earth does influence the direction of rotation of large weather systems and large vortices in the oceans, for these are very long-lived phenomena and so allow the very weak Coriolis force to produce a significant effect, with time." [1] As a result, hurricanes and tropical storms that form in the southern hemisphere spin clockwise while those that form in the northern hemisphere spin counterclockwise. 

The Night Sky

Most people aren't terribly adept at picking out constellations in the night sky, but just about everyone who lives in the northern hemisphere is familiar with the Big Dipper (Ursa Major) and the North Star (Polaris). However, I suggest you don't go looking for the Big Dipper here in Argentina—you won't find it. 

Instead, if you look to the south, you'll be treated to a view of the Southern Cross (Crux), one of the most recognizable constellations in the southern hemisphere. "It is easy to locate simply by looking for four bright stars all less than five degrees apart. Five degrees is about the width of your three middle fingers held at arm's length." [2] As with most constellations, you'll have to use your imagination, but if you picture a cross lying on its side in the upper left-hand corner of the photo below, there you have it. 

Southern Cross Leads the Way by bloke_with_camera, on Flickr [Creative Commons]

"Because it is not visible from most latitudes in the northern hemisphere, Crux is a modern constellation and has no Greek or Roman myths associated with it. Crux was used by explorers of the southern hemisphere to point south since, unlike the north celestial pole, the south celestial pole is not marked by any bright star." [3]

Much to my delight, my favorite constellation Orion is visible in both hemispheres; however, Orion looks a bit different here. Viewing the constellation from my perspective here in the southern hemisphere, Orion is upside down.

This article highlights differences between the night sky in the northern and southern hemispheres.

Animal Migration

Down here below the equator, even the migratory habits of the critters are different. Humpback whales spend the southern hemisphere summer in the food-rich waters of the Antarctic, and then they head north to balmier climes for breeding season. [4]

In terms of our fine feathered friends, it seems that "bird migration is a mainly northern hemisphere phenomenon. The lack of wide expanses of land in the southern hemisphere leads to a more stable climate and less overall seasonal movement of organisms." [5] Those species that do migrate to escape colder temperatures head north rather than south.

Whooper Swans by nickpix2009, on Flickr [Creative Commons]

For more information about this topic, you can read an overview of South American austral migration by researchers at the University of Florida.

[Photo Credits: puroticorico, Digit_AL, bloke_with_camera, and nickpix2009]

[1] Bad Coriolis
[2] Observing the Constellation Crux
[3] Crux – The Southern Cross
[4] Southern Whale Migration Overlapping Northern Whale Breeding Grounds
[5] Tree Swallow Migration Using Matrices

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