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So actually, you can pretty much listen to them all the time because lightning strikes Earth constantly, about a hundred times per second.
所以事實上，你幾乎一直都在聽這些電波，因為地球上不斷有閃電發生，大概每秒一百次。
Even if there is no lightning where you are, with a VLF radio, you can hear the crackling from storms that are thousands of kilometers away.
即使你所在的地方沒有閃電，但是有了VLF接收器，你能聽到幾千公里以外的暴風雨產生的動靜。
However, some times of day are better than others for picking up VLF waves.
但是，一天中有些時候比其他時間更適合接收VLF聲波。
Daytime isn’t as good as night time, for example. And what’s more, my colleague Denis Gallagher says, and in my opinion, he’s right.
比如白天不如晚上。而且，我的同事Denis Gallagher說，就我看來他說的很對。
He says the best time to listen for them is around sunset or sunrise.
他說聽這些聲波最好的時間是在日落或日出的時候。
That’s when there’s natural waveguides in the local atmosphere.
那是當地空氣中的自然波導出現的時候。
Did you say waveguide?
你剛才說了波導嗎？
Yes, a waveguide. Usually it refers to a device, like a metal conductor that’s used to guide and direct waves.
是的，波導。通常它指的是一個裝置，比如用來引導和控制電波的金屬導體。
But waveguides also occur naturally. They make a path for radio waves to follow in our atmosphere.
但是波導也會天然產生。它們為無線電波在我們的大氣中開辟了一條遵循的軌道。
These natural waveguides occur when the Sun is rising or setting, which makes sunrise and sunset good times to pick up VLF emissions.
太陽升起或落下的時候這些天然的波導就會產生，這就使得日落或日出成為了接收VLF發射的好時機。
Now, there are a few different sounds that you can hear on a VLF receiver, because when lightning strikes,
在一個VLF接收器上能聽到好幾種不同的聲音，因為出現閃電時，
the radio waves travel different distances and in different ways before they reach the receiver.
無線電波在到達接收器之前會經過不同的距離和不同的路徑傳播。
Some really interesting ones are called whistlers.
一些非常有趣的電波叫做嘯聲信號。
