6 January 2021

The desert dips below freezing on winter nights but if you want ice in the summer, how do you get it? This is a story of human innovation using natural processes.

In the 17th century BCE the Persians (Iranians) figured out how to make ice in the desert and store it through long hot summers. They used this method for 3,600+ years until electric refrigeration replaced it in the 20th century.

Though water is scarce in Iran, the method works well because the air is so dry. The process requires many steps: deliver water, make ice, store ice and keep it cool.

Deliver water to the ice-making location: The Persians built underground water channels called qanats to deliver water from uphill wells to the downhill population. Water in the qanat does not evaporate in the sun and stays cooler because it’s underground.

Make ice: To make ice the Persians built plaza-like ponds, shaded by a high wall, where the shallow water froze on winter nights. Collecting the ice before sunrise, they stored it in the ice house (dome in the background). Here are two photos of the same ice plaza no longer in use. People give it a sense of scale.

Store the ice: The ice house, called a yakhchal, stored ice underground, where conditions are naturally cooler, and protected it with an insulated dome. The hole at the top of the dome allowed hot air to escape.

Keep the ice cool: The ice was kept cool using natural ventilation to draw in cold air and remove hot air. Windcatcher towers in some towns were quite ornate.

Here’s a video that puts it all together.

Very cool!

(photos from Wikimedia Commons; click on the captions to see the originals)

21 December 2020

Today is one of two days per year when the sun stands still.

By the time you read this article the December solstice has already happened. The sun paused over the Tropic of Capricorn at 10:02 UTC, the same moment everywhere on Earth. In Pittsburgh it occurred at 5:02am local time, more than two and a half hours before sunrise.

If you wanted to experience sunrise and the December solstice simultaneously the best place would have been Georgetown, Guyana where the sun rose at 5:59am and the solstice occurred 3 minutes later at 6:02am local time (GYT). It’s too late to do that this year but 2021 is a possibility. By then we hope to travel safely thanks to the COVID-19 vaccine.

The good news for now is that the days are already getting longer in Pittsburgh. Tomorrow will be 3 seconds longer than today.

(photo by Fir0002/Flagstaffotos via Wikimedia Commons; click on the caption to see the original)

p.s. I am old enough that… I cannot think of Guyana without remembering the Jonestown, Guyana massacre orchestrated by cult leader Jim Jones on 18 November 1978. 918 people died in the mass murder-suicide. It is the origin of the phrase “Drinking the Kool-Aid.”

16 December 2020

An event of astronomical proportions will happen on Monday 21 December 2020 when two bright planets — Jupiter and Saturn — converge in the night sky, visible just after sunset.

A “conjunction” occurs when two astronomical bodies appear close to each other as seen from Earth. This one is called “Great” because it involves the two largest planets, Jupiter and Saturn.

A Great Conjunction happens every 20 years but this one is rare, as NASA explains:

It’s been nearly 400 years since the planets passed this close to each other in the sky, and nearly 800 years since the alignment of Saturn and Jupiter occurred at night, as it will for 2020, allowing nearly everyone around the world to witness this “great conjunction.”

— NASA: The Great Conjunction of Jupiter and Saturn

When Steve Gosser took the photo above on Friday 11 December the two planets had not yet converged but you can see Saturn’s rings at top left and Jupiter with four moons at bottom right (the fourth moon is faint in the bottom right corner).

See the Great Conjunction yourself using NASA’s sky map …

.. and check these websites for the cloud forecast at sunset in your area.

• National Weather Service sky cover
• Clear Dark Sky for North America
• Pittsburgh Clear Sky Chart

Sunset in Pittsburgh is at 4:57pm on 21 December. Unfortunately our sky will be overcast that evening.

Learn more in this video. Get an astronomy app at this link: https://www.secretsofuniverse.in/top-5-astronomy-apps/.

(photo by Steve Gosser, sky map from NASA/JPL-Caltech)

6 December 2020

The National Weather Service forecast for Pittsburgh is:

Today Cloudy, with a high near 35. Northwest wind around 6 mph.

— National Weather Forecast for Pittsburgh, PA, 6 December 2020 at 7am

Cloudy? Nope. Overcast! Here’s what it looks like in my neighborhood at 7:30a.m.

We call this Pittsburgh Gray.

(photos by Kate St. John)

p.s. It is hard to keep a positive attitude when the sky looks like this and our hospitals are overwhelmed with COVID patients. Hang in there! Take a walk. Sit among the birds.