When And Why – What Are The Hottest And Coldest Parts Of The Day?

When it comes to understanding the weather cycle of a single day, what many people are often told is a misunderstanding of how it works. More specifically, it is a misunderstanding of how air temperature works during the stages of the day.

Aside from it being an interesting piece of trivia information that people often enjoy when they learn, it has some pretty serious consequences for people.

When And Why - What Are The Hottest And Coldest Parts Of The Day

Getting the hottest part of the day wrong, especially without proper preparation, can mean that a person mistakenly goes out at the hottest part of the day, thinking the worst of the heat has passed, only to develop eat stroke later in the day, or worse!

By the same token, miscalculating when the coldest part of the day can result in a person going out at a warm time of day whilst they think it is cold, potentially finding themselves overheating.

And, going out at the coldest time of day when you think otherwise can run the chance of getting precious body heat sapped at an important time of day.

To help avoid these issues during the day, both mild and not-so mild, we have created this guide to help explain to you what exactly the hottest and coldest parts of the day are, and why that is.

We’re also going to be explaining why exactly the times that people think are the hottest and coldest parts of the day are wrong, as well as some other factors that can have a noticeable effect on air temperature.

Misconceptions On The Hottest And Coldest Part Of The Day

So, before we go any further, we should probably first help clear up the misconception that surrounds heat and what the extremes of the day are exactly, and why that is.

First, getting the warmer side of the equation out of the way, many people assume that the hottest part of the day is sometime around… well, midday, around noon.

This seems like it makes sense at first, and without added context, it is not hard to see why.

It is the time when the sun is the highest over the hemisphere that we see it on, so naturally, we would assume that this is the time when the most solar radiation is absorbed into the atmosphere, creating that heat.

By the same token, many people assume that the coldest part of the day is the exact opposite point when the sun is as far away from our horizon as possible, so around midnight, give or take an hour roughly.

However, these times are incorrect, and by quite a margin in some cases.

The Truth

The main factors that will often affect the temperature of the day, are the speed at which solar radiation is absorbed through the atmosphere, as well as the ability of the Earth’s atmosphere to absorb that heat energy.

Keep in mind that, although the light radiation from the sun can be received on earth within just a few minutes, the time it takes for that solar radiation to convert into heat energy is not the same

Add to the fact that the sun is still transmitting light and heat radiation to the Earth long afternoon, especially during summer, along with the fact that the earth is very good at absorbing and retaining heat energy within its local area for a time, and you have hottest and coldest times of the day that can seem divorced from when the sun is at its highest and lowest for us.

The Hottest Part Of The Day

So, now that we have hopefully dispelled some of the misconceptions about the heat during the day, it is now time to explain when exactly the hottest part of the day is.

Taking into account that the earth continues to absorb and retain heat after when the sun is at its highest in the day, the warmest time during the day is usually between 3 and 5 hours after noon.

For most places, this will mean that the actual hottest time of the day is any time from 3 pm, all the way to as far as 5:30 pm.

When And Why - What Are The Hottest And Coldest Parts Of The Day

Why Is The Hottest Part At This Time?

So, why exactly is it that 3 to 5 hours after noon is the hottest time of day, and not during noon, as we may have previously thought?

Well, this is in part due to the phenomenon that scientists call the ‘Thermal Response’ principle.

This is the premise that, as we already mentioned, the earth continues to absorb and retain the solar radiation that it has received from the sun so far during the day, whilst it is continuing to be bombarded with radiation from the sun as the afternoon continues to draw on, allowing the overall temperature to continue building during the early afternoon.

This means that the temperature of the day will start to plateau around the same time that the Earth no longer continues to receive a lot of solar radiation from the sun.

At this point, the Earth’s surface starts to lose its ability to retain the heat it has built up, releasing it back into the atmosphere from the surface, and is not replaced by new solar radiation.

Because the time that the Earth is exposed to the sun during the day can be affected by the seasons, this heat peak of the day can vary quite a lot depending on the tie of year it is, hence why there is a space of several hours over which this process can take place

The Coldest Part Of The Day

So, if the hottest time of the day is delayed by at least a few hours, then it would make sense that the same is true for the coldest time of the day.

So, it must be a few hours after sunset, right? Maybe at some point around midnight, maybe in the early morning. Surely?

Well, it is later than that. A lot later than that.

Generally speaking, the coldest time of day is usually within an hour of sunrise, which can set the time to anywhere from 6 to 9 am!

Why Is The Coldest Part At This Time?

So, why is there so much more time from the warmest part of the day to the coldest point of the day? Surely, once the sun has started to rise over the horizon, the temperature should also start rising as well.

Well, you have to keep in mind that, contrary to what some people on the internet may want you to believe, the Earth is a sphere. This means that, when looking at the horizon, you also have to accommodate slightly for the curvature of the Earth itself.

What this means for observing a sunrise, is that when you first see the sun rise above that horizon, it is still actually a few degrees below it.

And because the atmosphere partially distorts how light energy is received from the sun (hence why sunrises and sunsets have such vivid colors), we see the edge of the sun before it fully starts to appear over the horizon, meaning that, although the light is being received, there is very little solar radiation being transmitted to the surface of the Earth.

And remember, solar radiation is the key energy source for heat once it arrives through Earth’s atmosphere and arrives at our surface.

Once the sun has disappeared over the horizon after sunset, the surface is steadily, but surely, dissipating that heat energy, meaning the Earth’s surface is losing heat until it can receive new radiation from the sun.

This is why the coldest time of day is just around the time of sunrise. It is the point at which the most amount of heat radiation has been lost, and only just starts to be replenished in a given area once the sun has started to rise above a certain point of the horizon.

And so the cycle begins again!

Factors That Can Affect Air Temperature

So, we have hopefully helped explain why the hottest and coldest parts of the day are not the times that you may have thought before that.

However, when it comes to the temperature that is experienced by people, there are even more factors that affect how hot or cold it currently feels for you right now.

Latitude

This is something that most people who have traveled to different parts of the world will be able to attest to. The closer to the equator you are, the warmer it seems to feel.

Whilst this is a combination of several factors, from where it is positioned regarding the Earth’s tilt, and the humidity of regions across here, the result is the same.

You effectively have a region of the Earth that receives a consistent amount of the same amount of sunlight, all year round, regardless of the seasons. 

Seasonal Differences

On the topic of seasons, how long the heat of the day is retained by the planet’s surface is also affected by the time of year that the area is currently experiencing.

Like many people who remember their school physics lessons will know, compared to our position about the sun, the earth isn’t fixed at a perfectly straight angle and is tilted slightly at its access.

This means that, depending on where the planet is regarding the orbit around the sun, a part of the earth will be receiving more sunlight, and for longer durations in the day. This manifests as the four seasons that we are all familiar with, which can make our daylight hours over 20+, or just a few.

Water And Land Distribution

Bodies of water tend to be more stable with temperature, as water is an excellent conductor of heat. As a result, cities, and towns near lakes, seas, and oceans, tend to have a more consistent and stable temperature all year round.

Final Thoughts

So, as you can see, the hottest and coldest parts of the day aren’t exactly as they might seem at first.

It might feel a little counter-intuitive at first, but once you get a grasp of the basics of how solar radiation interacts with our atmosphere, the picture starts to become a little clearer.

And now, you have the knowledge to help prepare you for those warm later afternoons, as well as some fun trivia to throw out there at a party!

Andrew Capper