Depending on which hemisphere you live in, June 20th may be the longest day or the longest night of this year for you. This asymmetry is the subject of many festivities here on Earth and used to help mark time passing throughout the year.

The Earth’s rotational axis is tilted with respect to the Sun. This means that at certain times during the year, the solstices, the Sun will be in the highest point of the sky for the Northern or the Southern hemisphere. Now, beyond just providing us long summer days and long winter nights, the solstice also impacts our atmosphere, ionosphere, and well, space physics. The tilt means that the Sun is heating up one hemisphere more than another and ionizing the upper atmosphere. By heating and ionizing the atmosphere, we have asymmetries which affect things like the height of the ionosphere and conductivity (how easy or hard it is for particles to travel along the Earth’s magnetic field).

So why does CUSIA and space physics care? Well, putting those asymmetries into models is very difficult and often computationally expensive. In addition to the tilt of the Earth’s rotational access, the Earth’s magnetic field is also tilted.

If you would like to learn, more please check out Capabilities Assessment Matrix entry on dipole tilt.