What is the phenomenon of straight-line propagation of light? Let's have a look. Physics Papers-Various Light Phenomena Eclipse and Lunar Eclipse are important astronomical phenomena, and they are examples of light propagating in a straight line in the same homogeneous medium. Physics papers-Total solar eclipse, partial solar eclipse, annular solar eclipse and other light phenomena can be divided into umbra, penumbra and pseudopenumbra. The orbit of the moon around the earth and the orbit of the earth around the sun are not completely round, so the distance between the sun and the moon is near or far. Therefore, during a total solar eclipse, the observer sees that the sun is completely covered by the moon in the umbra, which is called a total solar eclipse; In the penumbra, the observer sees that the sun is partially blocked by the moon, which is called a partial solar eclipse; In the pseudoumbra, the observer sees that the middle part of the sun is covered by the moon, leaving a halo around it, which is called an annular eclipse. When the moon goes around the earth until the sun and the earth almost rise and fall with the sun, the moon can't be seen from the earth. This time is called the new moon, and the solar eclipse seems to happen in the new moon now. The period of the new moon is about 29.5 days. However, the solar eclipse does not occur every 29.5 days, because the orbital plane of the moon around the earth and the orbital plane of the earth around the sun are not completely coincident, and there is an average angle of 5 9' between them. Therefore, birthday food will only be given when the intersection of the sun and the two orbital planes is within a certain angle. All kinds of light phenomena-total lunar eclipse, partial lunar eclipse and penumbral lunar eclipse are all phenomena in which the moon enters the shadow of the earth and the surface darkens. The earth has a shadow in the direction away from the sun, which is called the earth shadow. The earth's shadow is divided into umbra and penumbra. The umbra is not directly illuminated by the sun, while the penumbra is partially illuminated by the sun. When the moon goes around the earth and enters the shadow of the earth, an eclipse occurs. The whole moon enters the umbra and a total lunar eclipse occurs; Part of it enters the umbra, and a partial lunar eclipse occurs. Total eclipse and partial eclipse are called umbra eclipse. Sometimes the moon only enters the penumbra and does not enter the umbra, resulting in a penumbral eclipse. When the earth is between the sun and the moon, the side of the moon facing the earth is full of sunshine. Seen from the earth, the moon is bright and round, which is called hope. The cycle of an eclipse is the same as that of a new moon, and an eclipse will only happen within sight. However, because the orbits of the earth and the moon are not in the same plane and have an included angle of 5 9', not all eclipses occur all the time. Only when the moon moves near the intersection of two orbital planes will an eclipse occur. Physics papers-all kinds of light phenomena Because the umbra of the earth is much larger than that of the moon, the moon will completely enter the umbra of the earth during the total lunar eclipse, so there will never be an annular eclipse. When the eclipse occurs, the observation area on the ground is very large, which can cover half of the earth, as long as it is a clear night sky. Physics paper-all kinds of light phenomena umbra is a place where light can't reach at all. Bright edges can appear around the shadow area produced by point light source, which is the result of light wave and diffraction after encountering obstacles. The larger the light source, the smaller the umbra area. For example, the picture under incandescent lamp is very clear, and the picture under fluorescent lamp is very vague, that is, in comparison, incandescent lamp can be regarded as a point light source with a small luminous surface; The luminous surface of fluorescent lamp is much larger than that of incandescent lamp. The shadowless lamp used in hospital surgery is a large circular lampshade, which is composed of several to 10 bulbs alternately or annularly arranged. Each bulb has a mirror bulb, and the inner wall of the lower part of the bulb is plated with a layer of aluminum, which reflects the light evenly and softly to the whole bulb. In this way, each light bulb can shine on the operating table, which not only ensures sufficient brightness, but also leaves no shadow.