Jupiter has captured my imagination this month so on Throw Back Thursday (TBT) I’m pointing you to one of my favorite January topics: The Moons of Jupiter.
It’s a Jovian January.
Watch for another Jupiter post later this month.
(retouched photo of the moons of Jupiter by Don E. Stewart from Wikimedia Commons. Click on the photo to see the original.)
When the sky is clear on cold January nights, the planet Jupiter shines brighter than the stars. Step outside with binoculars and you can see up to four of its moons.
These are the Galilean moons, named for Galileo because he was the first to report them in 1610. He used an improved 20-power telescope that wasn’t even as good as today’s birding scopes. When the moons are in the right position you can see what Galileo saw — something like this.
However on the night of Friday January 23 you’ll need a real telescope to view them because three of the moons — Europa, Callisto and Io — will transit (pass across) the disk of Jupiter and cause eclipses on the planet.
Above, the Hubble Space Telescope captured Io playing “Me and My Shadow.” At one point on January 23-24 all three moons will play this tune.
Astronomy.com calls it a triple shadow transit. Click here for their drawing of what you’ll see in the telescope at 1:40am EST on January 24.
This is your last chance to witness Jupiter’s triple shadow transit until 2032, but it’ll take some preparation and luck to see it. You’ll need a telescope and the sky has to be clear.
In Pittsburgh we’ll have to cross our fingers. Our sky is usually overcast in winter.
(photo of Io and its shadow on Jupiter from NASA’s Hubble Space Telescope. Click on the image to see the original)
A fast moving cold front crossed western Pennsylvania yesterday. The wind roared and temperatures fell from 61 degrees F Sunday morning to 19 degrees yesterday afternoon. The weather news called it a clipper.
Technically it’s an “Alberta clipper,” described by Wikipedia as a fast moving low pressure area that typically affects the central provinces of Canada and parts of the Upper Midwest and Great Lakes.
Clippers start as warm moist wind from the Pacific that crosses the Rockies into Alberta. When the wind hits cold air on the Canadian prairies it becomes a storm that rides the jet stream on a fast track east. By the time clippers get to Pennsylvania, Alberta is rarely mentioned.
Though clippers sweep across the continent, they’re regional so if you live outside their zone — say in California, Colorado, or Florida — the word brings to mind the fast-moving sailing ships of the mid 19th century, famous for sailing through dangerous storms at Cape Horn (above). The weather system is named for the ship.
Yesterday’s clipper left Pennsylvania but now we’re in for real winter — a low of 1 degree F Thursday morning.
Fill your bird feeders! Birds need food to survive this cold.
(Clipper Ship at Cape Horn, painting by James E. Butterworth, public domain via Wikimedia Commons. Click on the image to see the original)
p.s. Here’s what clippers look like on eBay. 😉
(click on the clippers to see the original eBay photo)
Today is the earth’s perihelion, the moment each year when we’re closest to the sun.
Because the earth’s orbit is slightly elliptical, we’re always closest in early January and furthest in July (aphelion), a difference of about 3 million miles. This sounds like a lot but it’s tiny compared to the size of our orbit. The distance has no practical effect on our temperature.
… but …
When the earth gets close to the sun, the gravitational pull makes us speed up as you can see in the animation. Right now we’re moving about 1 km/second faster (2,237 mph) than we do in July and this does affect our seasons. The season surrounding early January (our winter) is 5 days shorter than the season surrounding early July. This is nice for us but too bad for Australia where their summer is short.
This animation shows our fast and slow progress but its real purpose is to illustrate earth’s orbital precession (in an exaggerated way).
Earth’s orbit is not a closed ellipse. Instead it tracks out a little further each time as if drawing a huge daisy in outer space without lifting its pencil. In 21,000 years we come back to where we started and trace the same daisy again.
(animation posted by WillowW on Wikimiedia Commons. Click on the image to see the original with documentation)
Seen from the Southern Hemisphere, there’s a cat’s paw in the sky.
The Cat’s Paw Nebula, NGC 6334, was first noted by John Herschel at the Cape of Good Hope in South Africa in 1837.
At -35 degrees declination it’s hard to see this footprint even on a clear night in Pittsburgh. Cat lovers will have to go south — far south — to get a good look.
This image was taken by the European Southern Observatory (ESO) in Chile.
(photo from ESO via Wikimedia Commons. Click on the image to see the original)
Today’s going to be a dark day in Pudasjärvi, Finland, where this photo was taken. Within the next 12 hours, the sun will reach its southern solstice(*).
Pudasjärvi is so far north (at 65° 22? 39? N, 26° 55? 04? E) that during the winter solstice the sun is up only 3 hours and 30 minutes, rising at 10:27am and setting at 1:58pm. At high noon it will be only 1.5 degrees above the horizon — barely risen — and to make matters worse the moon is New so it won’t provide any light at all.
The day will be brighter here in Pittsburgh with 9 hours and 17 minutes of sunlight — as soon as the heavy clouds open up and allow the sun to shine.
Starting tomorrow the days will get longer.
Things will get better. I promise!
(photo from Wikimedia Commons. Click on the image to see the original)
(*) The solstice is at 6:03pm Eastern Standard Time, 1:03am Eastern European Time.
If you live in southwestern Pennsylvania, when’s the last time you saw a shadow outdoors?
A review of weather data for the past 30 days shows the sky has been overcast or foggy every day except for three days near Thanksgiving and on December 7 and December 9.
We’ve had only five days with enough sunlight to make a shadow. Otherwise, we’ve seen only brief glimpses of sun.
Oh, for a moment when the clouds are broken! It will finally happen this weekend. Check the Pittsburgh Clear Sky Chart(*) to see how long it will last.
When the sun comes out, I’m going outdoors to make a shadow of my own.
(photo of Avenue Foch, along the Saint-Roch Square, Le Havre from Wikimedia Commons. Click on the image to see the original.)
(*) Astronomers use the Clear Sky Chart to find out when to view the stars at night.
The news was bad this week for the Marshall Islands, South Florida, the Netherlands and Lower Manhattan.
Contrary to earlier predictions, satellite data from Greenland’s ice sheet shows that climate change is melting it a lot faster than we thought. When all that land-based water melts into the sea, the ocean will rise and permanently flood low-lying land around the world, including the places I named above.
Why is it melting so fast? A big reason is the action of numerous superglacial lakes (i.e. lakes on top of the glacier) that form in the summer. The lakes collect ice melt but they also speed up melting because they empty all at once — downward! — and flow under the ice sheet, lubricating it and sending it much faster to the sea.
If you find this hard to imagine — or even if you don’t — click on the screenshot above (or here) to see a great video showing how this happens.
In the video National Geographic follows a group of scientists camped near a superglacial lake as they studied its development. One day the lake disappeared, but the weather was so foggy they couldn’t see what happened. All around them the ice they were standing on cracked and heaved and boomed. Scary!
When the weather finally cleared they retrieved the measuring devices they’d left on the lake bottom (now no more) and pulled the data.
The lake they’d camped next to — two miles wide and 40 feet deep — had emptied to the ground 3,000 feet below in only 40 minutes!
(screenshot from National Geographic online video. Click on the image to watch the show)
Have you ever seen these ice structures?
Needle ice forms when the soil is still warm and the air is freezing. As ice forms on the soil’s surface, it draws up subsurface water by capillary action and builds new ice from the bottom. The result is a structure that looks like needles or tiny barricades. Since there is very little soil above the ice it pokes into the air.
Later in the season when the soil freezes, needle ice forms underground as part of a frost heave. Click here to see a cut-away frost heave in Vermont.
This patch of needle ice formed above a seep at Moraine State Park last weekend. Downstream the ground was squishy but here it was forming ice that looked like tiny walls.
Watch for these ice sculptures on moist soil.
(photos by Kate St. John)
If our eyes could look deep into space we’d see the clouds in this stellar nursery in the Centaurus constellation, 6,500 light years away.
This pink glowing nebula and clouds of dust were photographed by the European Southern Observatory (ESO) at Cerro Paranal, Chile. The nebula’s formal name is IC 2944. Because it’s visible to the naked eye it has a nickname too: The Running Chicken Nebula.
According to ESO’s description, the clouds are Thackeray globules “under fierce bombardment from the ultraviolet radiation from nearby hot young stars.”
Click here or on the image to find out what will happen to the clouds.
If you know where to look on a clear night, you can see a running chicken in the sky.
(photo of stellar nursery IC 2944 by ESO, the European Southern Observatory at Cerro Paranal, Chile. Click on the image to see the original)