The Sun influences tides, although its tide-producing force is less than half the strength of the Moon’s. Solar tides interact with lunar tides. When the Sun and Moon are in quadrature, that is, at quarter moons, low tides are lower than average, which is known as neap tides.The twinkle, or scintillation, of stars, is caused by the turbulence in the atmosphere of the Earth. The atmosphere has many layers of turbulent (moving) air, which are different in temperature and density. When the light from a star passes through the atmosphere, each layer of air bends (or refracts) the light, usually in a random direction. Then, we perceive that the stars are twinkling.A light-year is a unit of distance used by astronomers in order to describe the distances to stars and galaxies. It represents the distance that light travels in one year. The speed of light in empty space is about 300,000 kilometers each second, which means that one light-year is equal to about 10 trillion km.The distance from Earth to Proxima Centauri, the nearest star beyond the solar system, is about 4.24 light-years because it takes light about 4.24 years to travel from Earth to Proxima Centauri (and vice versa).A solar eclipse occurs at New Moon when the Earth passes through the Moon’s shadow. This shadow has an umbra (an inner, uniformly dark cone-shaped region), and a penumbra (an outer, lighter gray fan-shaped area).A solar eclipse can be seen over a small portion of the dayside of the Earth. Its appearance depends on the observer’s location relative to the shadow. Observers located within the umbra can see a total solar eclipse, whereas those situated within the penumbra observe a portion of the Sun covered by the Moon (partial eclipse). Outside the penumbra, no eclipse can be seen.A lunar eclipse occurs only at Full Moon when the Moon passes through the Earth’s shadow. This shadow consists of two parts: umbra and penumbra, as the Moon’s.