# Perfect home run weather? Maybe not!

I know what you’re thinking about tomorrow’s Astros’ Divisional Opener: How could they NOT open the roof? The amazing weather we’ve had this week bringing clear, calm skies and lower humidity would seem ideal for a baseball game.

In fact, it is pretty ideal for fans. After all, with the low humidity we all just feel lighter and better--crisp air makes us feel fresh. But low humidity is not the perfect environment for slamming a home run! Why? That dry air causes more drag on the baseball than humid air.

Certainly that is counterintuitive--after all, the humid air seems to drag us! Our hair drags, our run around the park drags, the dog drags. We all seem to just slow down a bit, so wouldn’t humid air slow down the baseball? After all, doesn’t the baseball have to go through that humid air to get to the fence for a home run?

The basic science is really pretty easy to understand. Air has weight. If we call it “molecular mass” everyone has flashbacks of eleventh grade chemistry and freaks out. So let’s go with weight. Our air is largely nitrogen (N) and oxygen (O) with a bit of hydrogen (H), Argon and other gases.

Without getting into the weeds of grams per mole, suffice it to say that Oxygen has a weight of 16 and Nitrogen has a weight of 14 and in our air they are ‘diatomic’ or come in pairs: O2 and N2 which means that O2 weighs 32 while N2 weighs 28. Why does that matter? That’s the weight of dry air. Dry. It’s heavy.

You know water’s formula: H20--Two Hydrogens and one Oxygen. Two Hydrogens weigh just 2 and with the single Oxygen weighs 16, so the water molecule’s weight is only 2+16=18. That 18 is much less than the weight of O2′s 32 or N2′s 28. Humid air weighs less than dry air.

What does this have to do with a baseball? Pretty simple--the ball is traveling through the air and if the air is dry then it has to travel through heavier air. Baseballs go farther in humid, lighter air!

Take a look at this chart from Exploratorium.edu showing a homer hit at a 45-degree angle. They’ve considered a temp of 70° and standard sea level pressure (that would match Houston). A ball going 161mph goes FARTHER in hot and humid weather:

Considering the Minute Maid Park center field fence is exactly 409 feet from home plate, a homerun baseball just might not get there in a cold and dry atmosphere! Hot and Humid means more homers!! So the question becomes, roof open tomorrow? The 3pm temperatures will be 87° with a dew point temperature of 61° which is a hot and dry atmosphere. So I think I’d just keep the a/c on, close the roof, and hope Altuve finds the sweet spot!

Go Astros!

Frank

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