It seems like you might be thinking of an "X-ray" instead of an "a ray." There is no such thing as an "a ray" in the scientific context.

X-rays are a type of electromagnetic radiation. They are invisible to the human eye and cannot be seen directly. However, they can be detected and visualized using special equipment like X-ray film or digital detectors.

Here's what you need to know about X-rays:

* They are a form of electromagnetic radiation, just like visible light, radio waves, and microwaves.

* They have shorter wavelengths than visible light, which gives them more energy. This allows them to penetrate through many materials that are opaque to visible light, such as flesh and bone.

* They can be used for medical imaging, security screening, and industrial inspection.

* They are invisible to the human eye.

If you were looking for something else, please let me know and I can try to answer your question.