July 20, 2010
On your birthday, the Earth completed another orbit — 584 million miles traveled since your last celebration.
Lightning Over Athens
Birthday · July 20, 2010
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APOD published July 20, 2010. Credit: Chris Kotsiopoulos. A publication-date match, not a photo taken on your date. Independent of NASA.
Have you ever watched a lightning storm in awe? Join the crowd. Oddly, nobody knows exactly how lightning is produced. What is known is that charges slowly separate in some clouds causing rapid electrical discharges (lightning), but how electrical charges get separated in clouds remains a topic of much research. Lightning usually takes a jagged course, rapidly heating a thin column of air to about three times the surface temperature of the Sun. The resulting shock wave starts supersonically and decays into the loud sound known as thunder. Lightning bolts are common in clouds during rainstorms, and on average 6,000 lightning bolts occur between clouds and the Earth every minute. Pictured above, an active lightning storm was recorded over Athens, Greece earlier this month.
Image credit: Chris Kotsiopoulos