ESSENTIAL Health Considerations on Polyphasic Schedules: The ULTIMATE Course on the Dark Period

Using Three Noons to Determine the Timing of Your Circadian Rhythm

Three noons


The purpose of this lesson is to help you find ways to establish the shift of your circadian rhythm to a strict timing. In this case, that time will be the timing of your local noon, which is beneficial to use since it occurs at the same time every day around the year (not taking into account possible daylight savings time changes).

It is likely uncommon to hear of the existence of “three noons” and their importance for circadian shift. The circadian rhythm is a biological rhythm in charge of timing many bodily processes. Examples include:

  • Melatonin
  • Testosterone secretion,
  • The daily body temperature gradient
  • The peaks for most efficient SWS and REM sleep

Because these events happen at fixed timings, it is beneficial for people to be able to predict the timing of the circadian rhythm compared to the hours on the clock. This is possible with comparing the noon to the minimum daily temperature. But first, the term “noon” needs a specific definition. There are three types of noons to establish the circadian rhythm’s shift: solar noon, local noon and biological noon.

Solar noon

The solar noon refers to the timing when the sun is at the highest position in the sky.

  • This happens at the same time every day on a specific longitude (ignoring daylight savings time). Thus, it is a good event to compare to other set timings.
  • The solar noon intends to biologically happen at 12:00 pm. This means that an unshifted circadian rhythm would have its natural SWS peak at 9 pm – midnight; the REM peak will be at 6-9 am.

In this lesson, solar times will refer to events happening at a specific time past the solar noon.

Local noon

However, your time zone may not be in sync with the solar time.

  • For example, if solar noon occurs at 1 pm, it naturally shift your sleep peaks by one hour later. In this case, the peaks would be between 10 pm and 1 am, and 7 am and 10 am. This would be the local noon; in other words, the local time when the solar noon occurs.
  • Some countries have a shifted local noon for economic or cultural reasons. For example, Netherlands and Spain.
  • You can find the timing of your solar noon here.

As you will soon learn, knowing the time of the local noon is is not enough to determine the timing of the optimal sleep peaks. However, it but will will be an easy way to get a more accurate timing than relying only on the solar rhythm. Therefore, take your time to find out when your local noon is before returning to the lesson.

Biological noon

The third type of “noon” is the biological noon.

  • This is the time of the day that your body treats as noon.
  • Late-night use of electronic screens nowadays often alters the timing of the biological noon.
  • Establishing the timing of the biological noon is important to help you assess optimal time for sleep. Unfortunately, determining this timing is not as simple as looking at a clock.
  • Specific timings in the circadian rhythm can, however, be used as a marker for comparison with the natural, solar-based rhythm. This would serve to determine how big the circadian shift is.

So far, the easiest method for this is to monitor the body temperature gradient throughout the day.

  • The lowest temperature point happens at around 4:30 am1 on the natural solar rhythm. Thus, by comparing the timing of that event to the local noon, it is possible to determine the timing of the biological noon. 
  • Additionally, the timing of the noon is not necessary to establish the shift of the circadian rhythm. However, it helps some people understand it better.


Below are a couple examples to help understand these calculations practically. All times refer to the local time.

p0d1t.png (600×600)


The natural solar rhythm (baseline):
Minimum temperature peak: 6:00 am
Biological noon: 12 pm
SWS peak: 9 pm – 12 am
REM peak: 6 – 9 am





3hn67.png (600×600)



Example 1:
Minimum temperature peak – 7:00 am
Biological noon: 1 pm
SWS peak: 10 pm – 1 am
REM peak: 7 – 10 am




mf003.png (600×600)


Example 2:
Minimum temperature peak – 4:00 am
Biological noon: 10 am
SWS peak: 7 – 10 pm
REM peak: 4 – 7 am





4gell.png (600×600)



Example 3:
Minimum temperature peak – 8:30 am
Biological noon: 14:30 pm
SWS peak: 11:30 pm – 2:30 am
REM peak: 8:30 – 11:30 am




The accuracy of establishing the timings of the sleep peaks is possibly the following:
Solar rhythm < Local rhythm < Biological rhythm

Apparently, the difficulty will also follow that same system. It is much easier to just stare at the timings on this website than to calculate the shift of everything to your local rhythm. Still, the better you assess the optimal timings, the easier it will be to make sure that your polyphasic schedules would work for you.

But what if you weren’t happy with the results from the assessment of the biological noon? How do you shift your circadian rhythm to follow your orders rather than listening to its wishes?

Shifting the circadian rhythm

How do you use the dark period to actually shift the circadian rhythm?

  • Essentially, you can alter the timing for the minimum temperature peak by initiating the photoperiod at a different time.
  • The lowest temperature point happens at around 6:00 on the natural solar rhythm where you wake up at 08:00. Thus, by comparing the timing of that event to the local time, you can establish the timing of the biological noon.
  • The REM peak coincides with the minimum temperature peak, which facilitate the calculations.
  • The SWS peak presumably starts 15 hours after REM peak begins.

Using this knowledge, we can clearly see that if you wish to have a later core, shift the circadian rhythm with a later dark period first until the monophasic rhythm fully shifts. Afterwards, start a polyphasic adaptation after this shift.

Start of photoperiod Minimum temp. peak REM peak SWS peak
Day 1 09:00 07:00 07:00-10:00 22:00-01:00
Day 2 11:00 07:00 07:00-10:00 22:00-01:00
Day 3 11:00 07:30 07:30-10:30 22:30-01:30
Day 4 11:00 08:00 08:00-11:00 23:00-02:00
Day 5 11:00 08:30 08:30-11:30 23:30-02:30
Day 6 11:00 09:00 09:00-12:00 00:00-03:00

As the table shows (though again, only as an illustration):

  • After the start of the photoperiod shifts on day 2, it takes a while for the body to catch up with the change.
  • However, after this change, the body is essentially tricked into thinking that it is in a different time zone. Thus, a later core becomes adaptable.
  • Notably, it is possible to combine the circadian shift with a polyphasic adaptation to make both happen at the same time. However, the circadian rhythm is usually more resistant to shifts when you are sleep deprived. This means that it is best to complete the shift before starting the desired schedule.

Aiding the shift with temperature

When you attempt to shift your circadian rhythm, it can be useful to monitor the temperature gradient to assess when a shift has been complete. Shifting the circadian rhythm is easiest with the use of light cues for short distances. However, continuous use of light, food and higher temperatures would suit large distances.

It is currently unclear for what ranges of shifting these cues apply individually or together.

  • Nevertheless, a fair assessment is that shifting the circadian rhythm by more than 2 hours from the solar noon will require more than just light.
  • When you shift your circadian rhythm using temperature, the natural temperature gradient should shift in the same fashion as the examples above. This would help an earlier shift of the circadian rhythm move the ambient temperature maximum earlier.  A later shift would then move the maximum value to later hours. 

Body temperature monitoring

At this point in time, temperature monitoring testing on a large scale has been limited. The products below seem to be capable of continuously monitoring the body temperature. Nonetheless, they have not been tested. Thus, it is uncertain if these products would serve their intended functions with good results.

When several people have examined the optimal equipment for this, there will be more information in this page. Buy the products (with paid links) at your own risk; please research if they perform the necessary task for you before making the purchase.

  1. Win-health Wireless Body Thermometer
  2. Medisana TM 735 Bluetooth Thermometer


In conclusion, there are three noons.

  • Solar noon, which occurs at a set time each day.
  • Local noon, which determines when the solar noon occurs in local time.
  • Biological noon, that states how much bodily noon shifts compared to the other two.

This information is useful when designing a schedule. The purpose is to secure adequate sleep quality, especially on Dual Core and Tri Core schedules.


  1. Baehr EK, Revelle W, Eastman CI. Individual differences in the phase and amplitude of the human circadian temperature rhythm: with an emphasis on morningness-eveningness. Journal of Sleep Research. 2000;9(2):117-127. doi:10.1046/j.1365-2869.2000.00196.x. [PubMed]

Leave a Reply

2 thoughts on “ESSENTIAL Health Considerations on Polyphasic Schedules: The ULTIMATE Course on the Dark Period

  1. Hmm, I wonder why it says ‘Enroll’ for course & a lock symbol even though I clicked on enroll

    1. You would need to create an account on the website to view everything. If you don’t want to do so, you can see the abbreviated version in the Overview tab.

Comments are closed.