How cold must it be to see your breath?

Factual Questions
1

As I was walking from my Dorm to Classes today I was able to see my breath. No big deal, but Its the middle of October, and I live in Metro Atlanta.

I don’t remember what exactly the Weather forcast called for, but it was wrong.

I found out later that it was 45 degrees.

But it got me wondering… How cold does it have to be in order to see your breath when you exhale ?

That is :

I can see my breath, How cold must it be (temperature) ?

Bonus Round:

What exactly is the formula for Crickets chirping and Temperature?

Is 40 C = 40 F ? There is some number that is the same right? If not 40 I know ONE number only fits the same .

2

It’s -40.

3

40C is like really, really hot. (About 104F). I think you’re thinking of -40C, which is just about equal to -40F.

I have no idea about crickets.

4

As a rule of thumb, the temperature must be below 50 degrees (F) to see one’s breath. The phenomenon is dependent on a number of criteria, including pressure and humidity. It is possible to make one’s breath visible at room temperatures by partially pressurizing your exhaled breath.

5

The number I’ve always heard is 48 degrees F. but I don’t know how I came upon that tidbit or whether the extra precision is meaningful.

6

On a very humid day, with the right lighting, you can see your breath at 60°F.
Danalan’s 50°F is a good rule of thumb under common weather conditions.

7

That could be why I could never duplicate the right answer with " 40 " :smack:

8

They are exactly the same temperature.

9

A bit of Googling turns up several formulas. The first 3 I see are:

a. Count chirps in 15 seconds, add 39. Answer is degrees F.

b. Count chirps in 14 seconds, add 40 for answer.

c. Count chirps in 15 seconds, add 40 for answer.

So what’s the definitive answer? That probably depends on what cricket you’re listening to.

10

Formula for converting Celcius to Farenheit is:
F = (9/5)*C + 32

If looking for the temperature (call it T) where the number is the same on both scales:

T = (9/5)*T + 32

Multiply both sides by 5:

5T = 9T + 160

Take 9T away from both sides and multiply both sides by -1:

4T = -160

i.e. T = -40, as others have posted.

11

As previously stated, the visible appearance of exhaled breath depends on air temperature and humidity. Out here in Left Field, whenever within eyeshot of any (perhaps unreliable) outdoor thermometer, I have never seen anyone’s breath above 40° F.

Egregious hijack: regarding ideal gasses within a closed system, the Universal Gas Law states that: P1V1 / T1 = P2V2/ T2.

P1= pressure on gas1. V1=volume of container holding gas1. T1 = temprature of gas1. Similarly, P2= pressure on gas2. V2=volume of container holding gas2. T2 = temprature of gas2.

Variants include:

Charles’ Law: P1 / T1 = P2 / T2, holding volume constant.

Charles, Jacques–Alexandre–César (1746–1823), French physicist. Charles discovered the law that bears his name about 1787, and that discovery constitutes his only major contribution to science. His more significant achievements were in ballooning. He conceived the idea of using hydrogen as the medium of displacement and developed with his brother nearly all the basic features of modern balloon design.

Gay-Lussac’s Law: V1 / T1 = V2 / T2, holding pressure constant

(physics) the density of an ideal gas at constant pressure varies inversely with the temperature

Note: Charles’ Law is often (mis) attributed to Gay-Lussac.

Gay-Lussac, Joseph Louis. 1778-1850.

French chemist and physicist who isolated the element boron (1809) and formulated a law that explains the behavior of a gas under constant pressure.

Boyle’s Law: P1 * V1 = P2 * V2, holding temperature constant.

Boyle, Robert. 1627-1691.

Irish-born British physicist and chemist whose precise definitions of chemical elements and reactions began the separation of chemistry from alchemy. In 1662 he formulated Boyle’s law.

12

Just a few weeks ago, on a damp morning here in Chicago, I saw my breath and it was about 58-62F.

13

I think what we might be looking for here is the difference in temperature between the exhaled breath and the ambient air temperature, instead of a static temperature at which breath becomes visable. Some people will have higher basal temperatures (still within a normal range) than other people, and their breath would become visable at a different temperature.

14

Sure, after a big gulp of hot coffee warms your mouth, you can see steam at 80°F.

15

I have found that in winter months when I dash from the gym to my car after a long run, there is steam rising off my entire body. It’s really cool to watch.

16

I can get that stepping out of a shower(I like my showers burn the first layer of skin off hot).

17

Maybe I’m oversimplifying or not taking other factors into account, but to me it seems that the obvious answer is “whatever the dewpoint is”. If not, why not?

18

Temperature, humidity and pressure.

19

And at the other end, a cold mouth will reduce breath fog.

I was talking once to an actor, and he was talking about doing a TV commercial that was supposed to be a beautiful warm sunny day. Unfortunately, the day was cold and sunny (which looks fine on camera, so the shot went on). So the actors had to stand around with ice in their mouths between shots, so their breath wouldn’t show as they stood around in shorts pretending it wasn’t 45 degrees.

20

Suffering for their art, eh?