The Perseid meteor shower peaks on the morning of August 12. This year promises favorable observing without the moon in the sky during the shower. The meteors are the dust from comet that vaporize when they strike the atmosphere. Sirius may be visible in the southeast about 45 minutes before sunrise.
by Jeffrey L. Hunt
The Perseid meteor shower is long-considered the best shower of the year observed from the northern hemisphere. Other showers may have higher rates, but warm weather and the high elevation of the shower’s radiant before sunrise, as seen from mid-northern latitudes, promises good views.
Perseus is low in the northeast as the sky darkens after sunset. It is between the bright star Capella and the “W” of Cassiopeia. Earlier in the evening, the shower’s point of origin is lower in the sky. At the beginning of morning twilight, it is over two-thirds of the way up in the sky above the northeast horizon. The Pleiades star cluster is in the sky as well, to the right of Capella.
The shower is from the dust and debris from Comet Swift-Tuttle (officially known as 109P/Comet Swift-Tuttle). These dabs revolve around the sun, like the planets, but they are scattered along the comet’s highly-elongated orbit. Each August, our planet passes through the tiny fragments as they revolve around the sun. High in the sky, the particles vaporize and leave a flash of light in the sky – a shooting star, a meteor. Like driving through a snowstorm, the meteors emerge from a single point in the sky – the radiant – and they are visible anywhere in the sky.
Unlike random (sporadic) meteors, the Perseids can be traced back to Perseus. When you see a possible Perseid, literally follow the trail in the opposite direction. If it points to Perseus, then it’s likely from the shower. Sporadic meteors originate from anywhere in the sky.
Some meteors leave a temporary trail after they evaporate. Others can be quite bright or seen breaking apart.
Official projected rates of the shower range to 90 meteors per hour when the radiant is highest in the sky. This occurs after sunrise in the Americas. For the estimation that follows, the maximum rate of 90 meteors each hour is used.
The glare from bright city lights cut the visible rate by at least a third. So, the rate is 60 or less meteors each hour.
A single human’s eyes do not have a large enough field of vision to see the entire sky. More meteors are seen looking at the radiant, but the meteors occur anywhere in the sky. To watch the entire sky, five observers are needed, one to look above each cardinal direction and a fifth to look overhead. There will be overlap of observations when a meteor starts overhead and travels into the sight line of a second sky watcher in the group.
A single observer in or near a city can see maybe 1-12 meteors per hour. In a dark location, a single observer can see perhaps 12-15 meteors each hour.
In an area with lights, a group may count 5-35 meteors per hour. In a rural area, the group might count 70 meteors in the hour before the beginning of morning twilight.
In the Chicago region, morning twilight begins at 4:09 a.m. CDT, later in locations farther west in a time zone. For example, in Sawyer, Michigan – about 50 miles east of Chicago on the eastern shore of Lake Michigan and in the Eastern Time Zone – morning twilight begins at 5:09 a.m. EDT. Initially twilight only affects the dimmer meteors, but it soon takes over.
Meteor observing is a social activity. A Perseid meteor shower party may be in order this year. The night could be capped with the first view of Sirius, low in the southeast about 45 minutes before sunrise. 2021, August 12: The radiant of the Perseid meteor shower is about two-thirds of the way up in the northeast as morning twilight begins.
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