Alexandre Cherman

When does spring start?

Light Sail will launch on Spring 2016”. That was the first contact I had with the news about TPS’s Light Sail, and it was not a happy one. Not because of the news itself, but because of the way it was written.

Earth’s seasons happen due to two factors: the motion of our planet around the Sun (revolution) and the tilt of its axis, relative to the plane of said orbit. Each of these factors, by itself, would not cause the seasonal cycle; they have to be taken both to explain the comings and goings of the seasons.

There are some times of the year, due to the orientation of Earth’s axis, when both hemispheres get the same amount of light and heat. There are some other times that one hemisphere gets the better part of the deal. In December, it is summer in Rio, but in London will be cold, very cold! And that is something we learn early on: seasons are switched between the hemispheres. When summer hits the South, it’s winter in the North. And vice-versa. Northern Hemisphere spring equals Southern Hemisphere autumn.

Earth Seasons
Earth Seasons

Now back to the headline: when will the Light Sail be launched?

Spring, of course. But which spring? Northern or Southern? The reader has every right to call me picky (or worse); since that news were written in the Northern Hemisphere, it is obvious that it refers to the Northern Hemisphere Spring. I do not trust obvious assumption very much, but I do agree: it must be the Northern Hemisphere spring.

The one thing I cannot agree with is that a society, which I admire and support, such as TPS (where the “P” stands for PLANETARY) would use this biased terminology and alienate half of the planet. A truly planetary society should think (and talk and write) free of any Hemisphere bias. Simple as that.

I was glad to see its website talking about an April 2016 launch (I can’t find the reference to spring anymore). Great! April 2016 I’ll be in the middle of Autumn. And people in the Northern Hemisphere will be in the middle of spring. And it will be April for everybody. Even for those who do not officially follow the Gregorian calendar, since it is considered the standard calendar in our global village… ■