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Sirius, Antares and other bright stars

The sparkling effect of some stars can be explained by different phenomena.
Bright stars in the sky

Sirius, the brightest star in our sky (visible especially in winter and spring), emits an intense bluish white light. It often appears to twinkle and change colour. Since it never rises far above the southern horizon, Sirius is particularly subject to this phenomenon.

Why do some stars sparkle?

A star’s twinkle and rapid change in colour are due to atmospheric turbulence. Stars are so far away that they appear as tiny dots of light, even through large telescopes. Before reaching your eye, their narrow beam of light must pass through mixing cells of warm and cooler air that splits light like a prism; the result is the changing colours you see.

The flickering effect is stronger on cold, clear nights, or when there is a change in air mass and the sky has just cleared. It is also more noticeable with brighter stars, especially when they aren’t very high in the sky.

Other shimmering stars to observe

Antares in the constellation Scorpius (especially visible in summer) is another star that remains close to the horizon. Though reddish in colour, this star sometimes gives off remarkable glints of green.

Other bright stars may also produce a similar effect. Consult the Monthly Sky page to identify the stars and constellations visible at this time of the year.

Although planets also appear to the naked eye as simple points of light in the sky, they actually exhibit a significant angular size, much larger than the distant stars. Planets are therefore less prone to twinkling and usually seem to shine more steadily.

Mysterious bright “stars” near the Moon

With respect to the stars, the Moon travels fairly quickly in the sky. Indeed, it moves around the celestial sphere and returns more or less to its initial position among the constellations in about 27.3 days. From one night to the next, the Moon moves about 12 degrees farther in the sky. Each month, the Moon moves close to naked eye planets and to certain bright stars. The planet or star you noticed near the Moon one night will be approximately in the same spot in the sky the next night, whereas the Moon will have moved eastwards (to the left).

Note also that as the Moon orbits the Earth, the angle it forms with the Sun and our planet progresses and the illuminated part transforms: the phase of the Moon changes.

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