He omitted a really big one - the beginning of spring. Most people are convinced spring begins at the equinox around 20th March but are also quite happy to talk about Mid-Summer's Day at the summer solstice around 20th June. Sorry, ya can't have it both ways. If the summer solstice is mid-summer then the spring equinox 3 months earlier must be mid-spring. It all boils down to how seasons are defined and here I find even astronomers can be really lazy in their thinking. Seasons are defined by the intersection of the Sun's apparent path and the equator so equinoxes are where the Sun's path crosses the equator and the solstices (Sun standing still) are the maxima and minima of the Sun's path. However, a maxima/minima can only be the mid-point of a season since points either side of a maxima/minima are equal in terms of the relative amounts of daylight. Seasons are defined by the amount of daylight, hence the summer solstice in the northern hemisphere, around 20th June, is the mid-point of summer when we celebrate "Mid-Summer's Day". All else follows from this and spring begins around 5th February in the northern hemisphere.