Here's why:

* Sunlight's Power: The sun emits a huge amount of energy, including ultraviolet (UV) radiation.

* Focusing Effect: During a solar eclipse, the moon blocks the sun's visible light, making it seem safe to look at. However, the sun's invisible UV rays are still focused through the small sliver of sun that remains visible.

* Retinal Damage: This intense UV radiation can burn your retina, the light-sensitive tissue at the back of your eye. This damage can be permanent and lead to vision loss.

Why looking at a partially eclipsed sun is worse than looking at a full sun:

* Pupil Dilation: When the sun is partially blocked, your pupils dilate, letting in more light. This makes your retina even more vulnerable to the concentrated UV rays.

* Reduced Blinking: You tend to blink less during a solar eclipse, further increasing the risk of damage.

Important Note: Never look directly at the sun, even for a brief moment, during a solar eclipse. Even if you don't feel immediate pain, damage can still occur.

Safe Ways to View a Solar Eclipse:

* Solar eclipse glasses: These are specially designed with a solar filter that blocks out harmful UV rays.

* Handheld solar viewers: These are similar to eclipse glasses but have a larger viewing area.

* Pinhole projection: Create a pinhole in a piece of cardboard and project the image of the sun onto a white surface.

Always consult reputable sources for information on safe viewing practices during a solar eclipse.