How to Tell Stars, Planets, and the Moon Apart in the Night Sky

Stars twinkle and appear fixed in patterns, while planets shine steadily and change their position among the stars; the Moon is the brightest object and changes its shape over time. In the night sky, stars are huge balls of hot gases that produce their own light, making them visible from Earth. They appear to twinkle due to the Earth's atmosphere bending their light. Planets, on the other hand, do not produce their own light but reflect sunlight, so they shine with a steady light and do not twinkle. Planets also move among the stars, changing their position over days and weeks. The Moon is Earth's natural satellite and is much closer to us than stars or planets. It appears larger and brighter, and its shape changes regularly. For example, if you look up at the night sky from your terrace, you might notice some points of light that flicker (stars), some that shine steadily (planets), and the large, bright Moon that changes its shape every few days. A common mistake is thinking that all bright objects in the sky are stars, but planets can be just as bright and do not twinkle.

The Moon appears to change its shape because different portions of its sunlit side are visible from Earth as it orbits us, creating phases like new moon, crescent, half, and full moon. This cycle is called the phases of the Moon and repeats about once every month. The Moon does not produce its own light; it reflects sunlight. As it moves around the Earth, we see varying amounts of its bright side. The phase when the Moon is not visible at all is called the new moon. As more of the Moon becomes visible, we see a crescent, then a half moon (first quarter), and finally, the full moon when the entire face is illuminated. After the full moon, the visible part decreases, leading back to the new moon. For example, if you observe the Moon every night, you will notice it grows from a thin crescent to a full circle and then shrinks back again. Many students think the Moon changes shape because clouds cover it or it goes behind buildings, but the real reason is its position relative to the Earth and Sun.

Constellations are fixed patterns of stars in the night sky; Saptarshi (Ursa Major), Orion, and Cassiopeia are three that can be recognised by their unique shapes, and the two end stars of Saptarshi help you locate the Pole Star. Saptarshi looks like a big ladle or a question mark and is visible throughout the year in the northern sky. The two stars at the end of its 'bowl' are called pointer stars; if you draw an imaginary straight line from them, it points to the Pole Star (Dhruv Tara), which always stays in the same position in the sky. Orion is known for its three bright stars in a row (Orion’s Belt), while Cassiopeia looks like a 'W' or 'M' shape. For example, during a clear night in winter, you can find Saptarshi in the north and use its pointer stars to spot the Pole Star, which helps in navigation. Some students think all stars move across the sky, but the Pole Star appears almost fixed because it lies nearly above the Earth's north pole.

Stars are not visible during the day because the Sun’s bright light scatters in the Earth’s atmosphere and makes the sky so bright that the faint light from stars gets hidden. The Sun is also a star, but it is much closer to us than other stars, so its light is very strong. When sunlight passes through the atmosphere, it spreads out in all directions, lighting up the whole sky and overpowering the much weaker light from distant stars. For example, even though the stars are present above us at noon, we cannot see them because the sky is flooded with sunlight. Some students think stars disappear during the day, but they are always there; we just cannot see them because of the Sun’s brightness.