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.

Now that the weather is colder here’s something to ponder: Why is it warmer on a cloudy night?

Some people say it’s warmer because clouds act like a blanket to hold in the heat but that’s not scientifically true.

Clouds are not holding in heat. They are emitting it!

Clouds absorb heat during the day just as the earth does. When the temperature falls clouds emit heat in all directions including downward to us below. Their warmth can be just enough to keep us above freezing.

On a clear night there is nothing to warm us so we have frost in the morning.

Did you know you can avoid frost on your windshield if you park beneath a tree on clear, near-freezing nights? The tree is emitting heat, too. No frost in the morning.

Either it is very cold in this picture or the car was not parked under a tree.

Read more about cloud blankets and other scientific “facts” that aren’t true at Dan Satterfield’s Wild Wild Science Journal.

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

In case you missed it last week …

Back in 2018 astronomers discovered a planet 200 light-years away and five times the size of Earth. K2-141b is a lava planet so close to its sun that its rotation and orbit are in lock step; the same side always faces the sun. It also moves really fast completing an orbit in only 0.28 days. Earth’s orbit takes a year. On K2-141b a “year” lasts 6.7 hours!

All of this was so intriguing that astronomers from York University, McGill University, and the Indian Institute of Science Education and Research decided to model K2-141b’s atmosphere. Published in the Monthly Notices of the Royal Astronomical Society, their report attracted attention because K2-141b is so unbelievably hellish. For instance:

The planet rains rocks, has an enormous lava ocean over 60 miles deep, and winds whip across its surface at speeds more than four times the speed of sound. And, because of how the small planet moves around its sun, one part of it experiences permanent daylight and reaches temperatures up to 5,432 degrees Fahrenheit, while the other side exists in permanent darkness, and temperatures drop to negative-328 degrees.

— The Cut: Astronomers Discover … Earth?? by Madeleine Aggeler

Put all that together and you get a place hot enough to evaporate rock, windy enough to transport the evaporated minerals rapidly to the other side of the planet, and cold enough on the dark side for minerals to condense quickly and fall as a rain of rocks!

Oh fun. K2-141b is more hellish than Dante’s Seventh Circle of Hell.

There are a few — mercifully few — places on Earth where it rains rocks. The eruption of Krakatua, above, is one of them.

Read more at Wikipedia and at The Cut: Astronomers Discover…Earth??

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