This animation reproduces an experiment that you can carry out at home or in the classroom.
We place a light source inside a cardboard box in which all interior walls are painted black (to limit light diffusion), except for the one at the bottom of the box which will be painted white to serve as a screen.
When the light source is lit in front of an opaque object, we can define various zones of shadow. In all cases, the shadow corresponds to the region that is not reached directly by the source’s light.

A light source doesn't create a shadow ! Light sources create light  !
When you commonly say that light hits an object and casts a shadow, you have to understand that light doesn't reach the area behind the opaque object - the area we call the shadow.
In fact, the brightness behind the object remains the same if you switch off the street lamp in front of it. Seeing a shadow is just a question of contrast.
If you want to build a world without any shadows, then you have two solutions:

• Switch off all light sources.
• Switch on many light sources everywhere !

Light rays travel in straight lines from the light source. Studying a shadow's shape is an important proof  of this characteristic of light. The light source here is supposed to be a « point source ».
The shadow of an object on a screen is the area of the screen which is not reached by rays from a light source.
A common misconception is that a light source creates a shadow behind an object. In fact, the source adds light to areas all around the shadow, and it is the resulting contrast that makes the shadow appear.
The form of the shadow depends on the relative positions of the source, the object and the screen.

The observation hole allows us to analyze the scene from a complementary point of view. If a source is not observable from the hole because an object is interposed between it and the observer, this implies that the hole is in the shadow of the object generated by the source and that the corresponding zone of the screen is not being illuminated by that source.
The shadows will appear closer if the sources are placed closer to each other. They can even overlap if an observer is located at the intersection of both shadows, from where none of the sources is visible. This zone is darker than individual shadows, from where one of the sources, but not the other, would be visible. This observation can be used as a first approximation to the concept of penumbra, since the two point sources can be interpreted as elements of an "extended source".

An animation to create day and night!
This photomontage allows you to turn on or off various light sources. We distinguish primary sources (the sun, the stars, or a lamp) and the secondary sources (the Moon or any reflecting object).
We also illustrate that shadows only appear in contrast to the supplementary light created by a source.

Never stare at the sun without proper eye protection.

An eclipse of the Sun can only occur at New Moon when the Moon passes between Earth and Sun at the correct distance. (The Moon’s orbit around the Earth is slightly elliptical).
The corona can only be safely viewed without the solar filter during the few brief minutes of totality --  that is,   when the Moon blocks the entire face of the sun.
The rest of the time, you have to use the appropriate solar filter and never look directly at the Sun without proper eye protection.

The Earth moves around the sun but, in our terrestrial frame of reference, the sun seems to move around the Earth. This periodic motion is the basic principle underlying the sundial.  The shadow cast by the “gnomon” indicates the hour of the day.