Background: The Blue Hill Observatory, near Boston, Massachusetts, is the longest-running weather observatory in the U.S. There, they have been measuring weather variables like annual temperature, amount of rain, etc. since 1885. They have also kept track of the date when there were ripe blueberries each year (perhaps the site operator liked to eat them!).  

The graph shows the date of first ripe blueberries each year since 1886 at the Blue Hill Observatory. The Y-axis is given as “Day of Year”. It is the day of the year if you start with one on January first, and just keep counting, not stopping and re-starting the count each month. So, February 1st is actually the 32nd day of the year.  The black line going across at Day of Year 172 is around the first day of summer – about June 21. The black line that stair-steps up and down is the day of ripe blueberries, and the red and blue lines show the 10-year and 30-year mean, which let you see the pattern a bit more clearly by smoothing out some of the bumps. 

Data Source: Blue Hill Observatory;

Note: a Julian Day (day of year) converter: