Why can the light beam from the theater's movie projection can be seen?

What you see are particles of dust in the air, illuminated by the projector's beam.

Why can the light beam from the theater's movie projection can be seen?events

fine dust particles suspended in the air refract the bright light showing up the lights path or beam.

Why can the light beam from the theater's movie projection can be seen?home theatre opera theater

fine dust particles suspended in the air refract the bright light showing up the lights path or beam. Is Correct!
This is called scatter. The sky scatters the blue light from the sun more than the other colors, causing the sky to look light blue.

Similarly, in a dark room and a bright projector beam, you're seeing a combination of blue scatter from the air molecules, smoke, etc., as well as scatter from dust particles. You can tell the difference by the degree of sparkling. Dust particles will appear as points of brightness, while the more uniform glow comes from air molecules, smoke, etc.
because the path of light from the projector is filled with tiny particles that float around (like dust maybe).... and then when light hits these particle, light is reflected from them so we are able to see them....