Do we see the entire Sun from Earth?

Is there a far side of the Sun that remains unseen, like the Moon?


At any one time we can only see the half of the Sun that is facing us. However there is no ‘far side of the Sun’. Unlike the Moon, which spins once for every time it goes around the Earth, constantly presenting us with the same side, the Sun spins once every 24.5 days and the Earth moves within its orbit so that over the course of about a month we get to see the entire surface.

However the Sun is a dynamic, constantly changing ball of fusion and by the time we see the other side, the entire surface has evolved and changed. And with our ever-increasing dependence on satellite technology, the problem of solar flares and coronal mass ejections is one that concerns scientists and engineers.

In order to better understand the evolution of space weather, a view of the entire Sun at once is required, and we obtained this for the first time in February 2011 when the STEREO mission reached its objective. Launched in 2006 these two almost identical spacecraft were designed to orbit the Sun in opposite directions, giving us a 3D view of the Sun and for the first time in 2011 allowing us to view the entire solar sphere. And as they move further along their orbit to pass behind the Sun, the Solar Dynamics Observatory will be giving us a full view of the near face allowing us 360 degree visual access for the next 6 years.

Because of the importance of the Sun’s light, heat and potential disruptive effect, the science gained from this mission will have a direct effect on us all.

Answered by Sophie Allan from the National Space Centre

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