Decoding shooting stars: what are they made of, and when is the best time to watch a meteor shower?
- These streaks of light in the night sky are meteors – small pieces of rock from space that are burning as they enter Earth’s atmosphere
- Check out our tips on when to watch the Geminid meteor shower in Hong Kong
This is an illustration of the asteroid, Phaethon, which is the parent object of the Geminid meteor shower. Photo: NasaImagine gazing up at the night sky when suddenly streaks of light whizz across your view. These shooting stars are meteors, which are small pieces of rock from space burning up in Earth’s atmosphere.
While it might seem like you have to be lucky to see one, there are certain times of the year when you’re more likely to see meteors.
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Where do meteor showers come from?
Comets are icy bodies made of frozen gases, rock and dust. As comets orbit the sun, solar radiation vaporises the comet’s surface, leaving behind trails of debris. This debris is what makes meteoroids. Meteoroids can also come from rocky objects in space called asteroids.
When Earth passes through a comet’s trails, many meteoroids enter the planet’s atmosphere at high speeds. They burn up and become meteors, creating spectacular displays of light known as meteor showers (see graphic).
Since the path of the comet’s debris around the sun stays the same relative to Earth’s orbit, we will always encounter certain debris trails at about the same time every year. This means we can see meteor showers roughly around the same time each year.
During a meteor shower, we are seeing the paths of many meteors that seem to come from a single point in the sky, called the radiant point.
This celestial event begins once the radiant point is above the horizon. As the radiant rises higher in the sky, the number of meteors increases. The best time to observe a meteor shower is when the radiant is at its highest point.
A measurement called the Zenithal Hourly Rate (ZHR) describes the number of meteors that can be seen every hour at the best conditions. But in reality, you will see fewer meteors every hour than the ZHR. This is because of how dark the sky is, how large your field of vision is, and how high the radiant is.
When can you see the Geminid meteor shower?
If you are interested in witnessing these dazzling lights in the sky, the Geminid meteor shower is taking place next week. With a ZHR above 100, this is one of the most spectacular meteor showers that happen every year.
However, observers in Hong Kong are likely to see only 20 to 30 meteors per hour even from remote sites that are away from the city lights and have dark skies.
In Hong Kong, the meteors might start appearing at around 7.30pm on December 14, but the best time to watch the Geminid is between 1am to 3am on December 15 when the radiant will be at its highest point in the sky.
You can see the meteor shower under a dark sky with no moon or watch the live stream from the Hong Kong Space Museum’s YouTube channel.
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