Cosmic Rays and Particles

Over the last month, those of you living in the West have been able to observe how particles in the air can change how cosmic rays are viewed by our eyes.  This last weekend in Portland, OR, the smoke from the wildfires in the region were blown in and focused the Willamette Valley, causing unhealthy air conditions (151-200 Air Quality Index).  The morning sun was red and throughout the day, the clouds and sun looked orange.

That is because the radiation from our sun that we see as red and orange are long wavelength, low frequency cosmic rays within the human visible light spectrum.  These colors are less likely to be scattered by atmospheric particles compared with the other visible light colors (yellow, green, blue, purple).  On days with high pollution or smoke, the sun and the clouds will appear red or orange because the other colors in the light spectrum are scattered by the air particles.

For more information, check out "the Physics Classroom".  You can also model this effect by shining a flashlight through a glass of water.  Watch the color change in the steam of light through the cup while using a dropper to add milk to the water.  It's a sunset in a cup!

Scale, Proportion, and Quantity

Looking for a good example of scale - both physically and mentally?  Here is an excellent video showing how big things can get in our universe.

Everything you need to know: Perseid meteor shower | Astronomy Essentials | EarthSky

Turn your eyes to the sky tonight 

- it's the peak night for the Perseid meteor shower!

Everything you need to know: Perseid meteor shower | Astronomy Essentials | EarthSky

By Bruce McClure


In the Northern Hemisphere, the annual August Perseid meteor shower probably ranks as the all-time favorite meteor shower of the year. This major shower takes place during the lazy, hazy days of summer, when many families are on vacation. And what could be more luxurious than taking a siesta in the heat of the day and watching this summertime classic in the relative coolness of night? No matter where you live worldwide, the 2015 Perseid meteor shower will probably be fine on the mornings of August 11, 12, 13 and 14, with the nod going to August 13. On a dark, moonless night, you can often see 50 or more meteors per hour from northerly latitudes, and from southerly latitudes in the Southern Hemisphere, perhaps about one-third that many meteors. Fortunately, in 2015, the waning crescent moon comes up shortly before sunrise, so you’re guaranteed of dark skies for this year’s Perseid meteor shower. Thus, on the Perseids’ peak mornings, moonlight will not obscure this
year’s Perseid meteors. Follow the links below to learn more.

When and how should I watch the Perseid meteor shower in 2015?
Don’t wait until the peak nights of the 2015 Perseid shower to watch for meteors this year. Start watching in the second week of August, when the Delta Aquarid meteor shower is rambling along steadily, reliably producing meteors each night. Then keep watching in the second week of August, when the Perseids are rising to a peak. The Perseid shower is known to rise gradually to a peak, then fall off rapidly afterwards. In early August (and even through the peak nights), you’ll see them combine with meteors from the Delta Aquarid shower. Overall, the meteors will be increasing in number from early August onward, and better yet, the moonlight will diminish until the new moon on August 14, 2015.

Don’t rule out early evenings As a general rule, the Perseid meteors tend to be few and far between at nightfall and early evening. Yet, if fortune smiles upon you, you could catch an earthgrazer – a looooong, slow, colorful meteor traveling horizontally across the evening sky. Earthgrazer meteors are rare but most exciting and memorable, if you happen to spot one. Perseid earthgrazers can only
appear at early to mid-evening, when the radiant point of the shower is close to the horizon.

As evening deepens into late night, and the meteor shower radiant climbs higher in the sky, more and more Perseid meteors streak the nighttime. The meteors don’t really start to pick up steam until
after midnight, and usually don’t bombard the sky most abundantly until the wee hours before dawn. You may see 50 or so meteors per hour in a dark sky.

General rules for Perseid-watching.
You need no special equipment to enjoy this nighttime spectacle. You don’t even have to know the constellations. But you’ll definitely want to find a dark, open sky to fully enjoy the show. It also helps to be a night owl. Give yourself at least an hour of observing time, for these meteors in meteor showers come in spurts and are interspersed with lulls.

An open sky is essential because these meteors fly across the sky in many different directions and in front of numerous constellations. If you trace the paths of the Perseid meteors backward, you’d find they come from a point in front of the constellation Perseus. But once again, you don’t need to know Perseus or any other constellation to watch this or any meteor shower.

Enjoy the comfort of a reclining lawn chair and look upward in a dark sky, far away from pesky artificial lights. Remember, your eyes can take as long as twenty minutes to truly adapt to the darkness of night. So don’t rush the process. All good things come to those who wait.

What’s the source of the Perseid meteor shower?
Every year, from around July 17 to August 24, our planet Earth crosses the orbital path of Comet Swift-Tuttle, the parent of the Perseid meteor shower. Debris from this comet litters the comet’s orbit, but we don’t really get into the thick of the comet rubble until after the first week of August. The bits and pieces from Comet Swift-Tuttle slam into the Earth’s upper atmosphere at some 210,000 kilometers (130,000 miles) per hour, lighting up the nighttime with fast-moving Perseid meteors. If our planet happens to pass through an unusually dense clump of meteoroids – comet rubble – we’ll see an elevated number of meteors. We can always hope!

Comet Swift-Tuttle has a very eccentric – oblong – orbit that takes this comet outside the orbit of Pluto when farthest from the sun, and inside the Earth’s orbit when closest to the sun. It orbits the
sun in a period of about 133 years. Every time this comet passes through the inner solar system, the sun warms and softens up the ices in the comet, causing it to release fresh comet material into its orbital stream. Comet Swift-Tuttle last reached perihelion – closest point to the sun – in December 1992 and will do so next in July 2126.

Although the Perseid meteor shower gives us one of the more reliable productions of the year, the ins and outs of any meteor shower cannot be known with absolute certainty. Forecasting the time and intensity of any meteor shower’s peak – or multiple peaks – is akin to predicting the outcome of a sporting event. There’s always the element of surprise and uncertainty. Depending on the year, the shower can exceed, or fall shy, of expectation.

The swift-moving and often bright Perseid meteors frequently leave persistent trains – ionized gas trails lasting for a few moments after the meteor has already gone. Watch for these meteors to streak the nighttime in front of the age-old, lore-laden constellations from late night until dawn as we approach the second weekend in August. The Perseids should put out a few dozen meteors per hour in the wee hours of the mornings of August 11, 12 and 13.



"Perseid Meteors and Comet Swift-Tuttle" by Aanderson@amherst.edu - Own work. Licensed under CC BY-SA 4.0 via Commons.