Icy trail in Schenley Park, Feb 2015 (photo by Kate St. John)
Snow, sleet, rain, freezing rain.
From 5 degrees F on Thursday night to 53 degrees with freezing rain today, we’ve had it all. And there’s more to come. Tomorrow night will be 15 degrees.
This yo-yo weather reminds me of what we learned during the polar vortex in January 2014: Climate change is making the jet stream wobble so we get shots of very cold air and then warm air soon after, as shown in drawing(c) below.
Jet stream Rossby waves (graphic from Wikimedia Commons)
Be careful today! It’s variably icy out there.
p.s. I’ve used an old photo of ice because it’s too icy to step outside this morning!
(photo by Kate St. John. Drawing from Wikimedia Commons; click on the image to see the original)
Uh oh! Blue light, though bright, isn’t better at night.
As cities switch from incandescent or mercury street lights to LEDs they’re saving electricity and money and providing more light. But brighter isn’t better if it’s blue.
The video above shows how the color temperature of light matters to our eyes and sleep patterns. Though the video doesn’t mention it, the color also matters to birds and animals.
It’s possible to buy yellow-toned LEDs but blue, because its bright, has been the default choice for city lights. We didn’t know that color mattered when the world began switching to LEDs and the bulbs have such a long life it’ll be decades before it’s time to replace them. Meanwhile humans, birds and animals will be coping with the change.
p.s. Here’s a really helpful video showing the difference between incandescent, compact fluorescent and LED light bulbs in home use (the A19 screw base). You’ll also see the inside of an LED bulb. I was surprised to learn it’s a tiny computer.
That question would have been absurd 200 years ago because billions of stars were visible on every clear night.
But now with the prevalence of artificial outdoor light most of us cannot see the Milky Way and many children don’t know what it is.
Because of this, some ancient stories don’t make sense. In Genesis Abraham worried that he had no heir but God reassured him, “Look up into the sky and count the stars if you can. So many shall your descendants be.” Today we look at the sky and count 50 stars, not realizing that Abraham was overwhelmed.
So what are we missing? Sriram Murali traveled in California recording time-lapse video of the night sky in places with high light pollution (San Jose) and almost no artificial light (Death Valley).
His video let’s us see the sky as our ancestors did.
Spring tide at Wimereux, France, Sept 2007 (photo from Wikimedia Commons)
Despite the fact that it’s autumn we’re going to have a spring tide next week.
In this case the word “spring” has nothing to do with the season. Instead it means the ocean will be “springing up” in the highest high tide.
Spring tides occur a day or two after a full moon and are highest when the moon is closest to Earth at perigee. On Monday the moon will be full and at its closest perigee since 1948. Watch for nuisance flooding on Tuesday in low-lying coastal communities.
Perigee also makes the moon look larger, an effect called the supermoon. Here are two photos of the full moon in 2007, perigee on the left on October 26, apogee (furthest) on the right on April 3.
Size comparison of full moon at perigee versus apogee (image from Wikimedia Commons)
The difference is about 30,000 miles. Closer objects look larger. (Duh!)
If you miss this supermoon you’ll have to wait 18 years for it to be this close again.
In the olden days the first killing frost in Pittsburgh usually occurred by Halloween and we had to wear winter coats over our costumes while trick-or-treating. … I always hated to cover my costume.
This year has been very warm, even hot. Only ten days ago it felt like August and today the temperature is 5-10 degrees above normal. When will we experience the first killing frost?
Some of you already have. If you live east or north of Pittsburgh the growing season is shorter (bluer), as shown on the USDA Plant Hardiness Map below. Bradford, Pennsylvania is three growing zones colder than Pittsburgh and the Monongahela and Ohio Valleys. I’ll bet they’ve had a killing frost.
Pennsylvania within the USDA Plant Hardiness Map retrieved October 2016 (map from USDA)
Here in Pittsburgh the weather forecast says we won’t dip near freezing for the next several days. Today it’ll be 10 degrees above normal.
When do you think we’ll have our first killing frost?
The effect is too tiny to see. It takes 100 years for the day to gain 1.4 milliseconds. To put that in perspective, a day was 23 hours long for the dinosaurs and is close to 24 hours now.
The only way we can measure Earth’s rotation is by using an array of instruments stationed around the globe (VLBI) that precisely record their first sighting of certain quasars. We then crunch the data to arrive at the length of a day and add a second to our atomic clocks when necessary.