A Physicist's Temperature Blanket

I’m quite late to this concept - I only heard about temperature blankets last year. The idea is that you knit (or crochet) a row a day starting on 1st January with the colour determined by the temperature of the day (however you define it). You end up with a beautiful striped blanket or scarf with the colours showing the gradual warming and then cooling of the days (in the northern hemisphere). It is also a way to be more aware of the seasons as they change.

But there is no need to stick to the standard model and many amazing and innovative variations exist. My friend Katherine Haxton is doing squares for each month where the core of the square is the pre-industrial average temperature, and the outside is this years’ temperature which nicely shows the impact of the climate crisis.

So what does a physicist do when they want to knit a temperature blanket that isn’t a temperature blanket?

I decided to take inspiration from our solar panels - we are very lucky to have a system which (in theory) gives lots of data about how they are performing, including the power being generated as well as the energy generated each day (in kWh). I decided to use the energy generation per day as the basis for my blanket. To make things slightly more difficult our system stopped working last year so I’m using data from 2019. Although it's a shame not be knitting exactly what is happening this year, the advantage of this is I can knit a few days ahead if I feel like it as I already have the data.

The first task then was to write a python script to automatically download the data I needed for each day. The system has an API which made this relatively straightforward (ish).

I also decided to make things a bit more complicated by changing the row length so that it is proportional to the length of day. For this reason my blanket actually starts on 21st December.

Shape of the Blanket

The blanket should have a curved shape (does this have a name??) peaking on June 22nd. Now we are at the end of March we have just passed the spring equinox, so there is an inflection point in the curve - the rate at which the rows are increasing has stopped increasing!

To work out the row lengths I first needed to download a template for excel which can calculate day length for a given latitude and longitude (I’m in Glasgow). I then used this data and scaled it so that the maximum row length was 305 stitches. Using DK wool this makes it about 1.63m wide at the biggest point and 112 stitches (60cm) at the narrowest.

For the wool I’m using stylecraft and some similar wool from my stash. I chose 10 colours in a range of purples and blues. The energy generation varies from 0 (when snow covers the panels) to 25 on a really sunny day at the end of May, which is not too different to the range for a standard temperature blanket. I manually fixed the colour bands so that they would give an interesting effect. For example during the whole of December it is rare for the panels to generate more than 2 units, so the first band is 0-1 and the second is 1-2.5. The bands get bigger after that.

I really enjoyed the planning process for this project and am loving seeing it come into being. Hoping this will be a blanket I will use time and time again.