What phenomenon is characterized by explosions on the sun?

The correct answer is solar flare. This phenomenon refers to intense bursts of radiation coming from the release of magnetic energy associated with sunspots. Solar flares occur when the magnetic field lines on the sun become tangled and suddenly realign, releasing energy that can be observed in multiple wavelengths, including X-rays and visible light.

Solar flares can significantly impact space weather, affecting satellite operations and communication systems on Earth. They are directly associated with the sun's magnetic activity, making them distinct from other phenomena like supernovae, which are explosions marking the death of a star, or stellar and planetary nebulae, which are clouds of gas and dust formed from the remnants of stars. These phenomena do not involve the sudden release of energy from the sun like a solar flare does.