21 March 2015

The word Analemma sounds like a girl’s name or perhaps an exotic fruit but in fact it’s the name for that figure 8 hanging in the sky above.  You won’t see it in Nature but you may have seen it as a symbol printed on an old-fashioned globe of the world.

Technically speaking an analemma is the location of one celestial body as viewed from another for one complete orbit.  Practically speaking it’s the Sun’s position throughout the year at the same location and time of day on Earth.   I was surprised to learn it’s a figure 8 but that’s because the Earth’s orbit is elliptical and tilted.

This photo took a whole year to create.  Every other week in 1998-1999, Jack Fishburn took a photograph of the sun’s position from his office window at Bell Labs.  He was careful to place the camera in the exact same position and snap the photo at the same time of day (correcting back to Standard Time during Daylight Savings).  After collecting a year of photographs he overlaid them to create the analemma.

Tunc Tezel did the same thing at Baku, Azerbaijan and made it a movie here.

You can create your own analemma if you’re persistent (one whole year) and precise (same camera location and time of day for every photo) and have access to Photoshop.

When you’re done you’ll know that the top of the 8 is the summer (northern) solstice, the bottom is the winter (southern) solstice, and the crossover point is both equinoxes.  Today, one day after the Northern Equinox, the sun is very near the center of the analemma.

(photo by Jack Fishburn via Wikipedia GNU Free License. Click on the image to see the original)

Mountains in Alaska?  No, my icy sidewalk.

Yesterday more than three inches of wet snow fell across Pittsburgh.  Sometimes it changed to rain.  Overnight it froze.

Expecting dangerous footing, I put on my ice cleats and went out to see.

Under light snow on the sidewalk … Viola, a glacier!

That’s not all.  Last night I noticed that my car, parked on the street, was standing in three inches of water because ice dams prevented the water from draining.  In the dark I heaved snow and water to the storm drain, hoping to prevent my tires from being locked in ice this morning.  What do you think? Am I stuck?

I spread salt and came indoors, feeling a little smug that my ice cleats worked so well.

But the ice has one more trick up its sleeve.

Heads up!

(all photos by Kate St. John, except the ice warning sign in Montreal is by Paul Joseph via Wikimedia Commons. Click on the sign to see its original)

With temperatures as much as 33 degrees below normal, western Pennsylvania is swamped in ice and long overdue for a warm spell.  When the weather breaks, so will the ice.

In some places we’ve already seen some flooding.  On Tuesday February 24 The Weather Channel wrote:

In western Pennsylvania, flood warnings have been issued for Armstrong and Clarion counties due to an ice jam that is blocking the Allegheny River, creating a backflow of water into Parker, according to an AP report. The warning is in effect until 7 a.m. Thursday. State Route 268 has been flooded and at least two people have been rescued from the floodwaters in Parker.

In February 2009 I was hiking at Raccoon Creek Wildflower Reserve when the ice broke and jammed in front of me.  Click here or on the gray-brown ice photo for my in-person (Throw Back Thursday) report.

(photos by Kate St. John: Ice and gulls on the Monongahela River at Duck Hollow, 25 Feb 2015.  Ice on Raccoon Creek, 8 Feb 2009)

Most of us were asleep at 4:50am on Tuesday morning when a 500-pound space rock hurtled into Earth’s atmosphere.  It was on its way to Pittsburgh.

Fortunately the meteor’s aim was off a bit — just enough to miss all the populated areas and disintegrate east of Kittanning.

Considering its early morning arrival we wouldn’t know about it if a few people hadn’t been awake.  Eyewitnesses reported seeing and hearing it on the American Meteor Society (AMS) website and NASA’s camera at Allegheny Observatory recorded its arrival in the video above.

Using eyewitness reports AMS generated a map of its trajectory.  Click and scroll down to see what it was aiming for.  Yikes!

We were lucky.  In an uncanny space-time coincidence a very big meteor whooshed over Russia two years and two days before the Kittanning event.  It weighed 10,000 tons(*) and injured over 1,000 people.  February 15, 2013 in Russia.  February 17, 2015 in Pittsburgh.

…What is it about February?

I wish I had seen it.  I was awake but I wasn’t paying attention.

(YouTube video of the February 17 fireball from NASA’s Marshall Center)

(*) that’s 40,000 times heavier than the meteor at Kittanning.

Whoa!   Is this a flying saucer?

No, it’s a lenticular cloud over Mauna Kea, Hawaii.  This was the Astronomy Picture Of the Day on August 21, 2005.

Click on the image to read more about it.

(photo from Wikimedia Commons. Click on the image to see the original)

21 January 2015

Continuing my Jovian January theme …

Yo! Did you know that Jupiter’s moon Io is the most volcanically active object in the solar system?

Io is the size of our Moon but a very inhospitable place.  It’s covered in sulfur which makes pretty shades of yellow but unbreathable air.

To make matters worse, Io is so small and Jupiter is so large that Jupiter’s gravity causes 100 meter land-tides on Io’s surface.  Yes, the land rises and falls 330 feet as Io orbits Jupiter.  No wonder Io has more than 400 active volcanoes!

In 2007 NASA’s New Horizons spacecraft took photos of a plume coming off the top of Io.  What was it?  A volcanic eruption rising 300 miles above Io’s surface!

See a video of Io in action. Yo, Io!

(video from Slate.com on YouTube)

p.s. Scientists to Io: “Your volcanoes are in the wrong spot.”

A week ago I found beautiful ice formations along the Butler-Freeport Trail at Monroe Road.

Water’s constant drip made a curling fountain.

And some of the icicles accumulated frosty teeth.

The weather was warming that day and part of this massive ice cliff …

… had crashed to the ground across the trail.

Here’s one of the smaller chunks near my boot.  I’m glad I wasn’t there when it fell.  Watch out below!

This weekend the weather has been unseasonably warm.

I wonder what the icicles look like now.

(photos by Kate St. John — taken with my cellphone because I forgot to bring my camera)

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)