THE BLACK MOON MADE ME FORGET SOMETHING I ALREADY KNEW.  BIG CORRECTION AT 10:45AM!  We never see the dark side of the moon except from outer space. Thank you, Tom Hoffman, for reminding me. (Shaking fist at Black Moon!)

30 September 2016:  Today the media is peppered with the ominous words “Black Moon.”  Here’s what that’s all about.

By the time you read this the moon has already risen in Pittsburgh at 6:46am. It came up half an hour before sunrise, will reach its zenith at 1:00pm, and will set at 7:07pm four minutes after sunset.  It’s in lock step with the sun.

But we won’t see it.

It’s a new moon traveling so close to the sun that the sun’s glare hides it.  And it’s not illuminated.  It is back lit by the sun.

This is the second new moon this month, the so-called “Black Moon.” Like its bright twin, the Blue Moon, two of these in a month are a relatively rare occurrence.  The last Black one was 32 months ago.

What about the dark side of the moon.  Is it always black?

No. Today’s Black Moon is sunlit on the other side.  But if we could see it, it would look unfamiliar.

During the new moon last July, the dark side of the moon was facing the DSCOVER satellite when NASA’s EPIC camera recorded time lapse photos.  Watch as the dark side flies by the southern hemisphere.  Doesn’t it look odd!

For starters, it’s darker than we expect.  Even when fully illuminated the moon is darker than Earth from outer space because it reflects less light.  Our planet is bright blue and white because it has lots of water.  The moon is dry and dark.  It matches the color of Australia.

Here’s the dark side in a still photo from August 2015.

Look closely and you’ll see that it’s missing the craters we always see.

Of course we shouldn’t expect the dark side to match the bright side.  But the fact that it looks so different makes this Black Moon unsettling.  😉

(New moon symbol from Wikimedia Commons. Moon and earth animation from NASA.  Click on the images to see the originals.)

It’s not the heat, it’s the humidity.  But its not the relative humidity.(*)

As a raw number, relative humidity doesn’t tell you anything.  The video above shows how the same amount of water produces different relative humidities depending on air temperature.

For example, early yesterday morning in my backyard it was 80 degrees with relative humidity 79%.  Last Tuesday it was 66 degrees with relative humidity 83%.

So didn’t yesterday’s 79% humidity feel better than 83% last Tuesday?  No!  Yesterday’s 80 degrees held a lot more water.

Dewpoint (the temperature at which the air is so saturated that it rains or produces dew) is the helpful number that tells us that.  If you know the temperature and relative humidity you can calculate the dewpoint here.

The National Weather Service in Chicago made a chart to describe how we feel at various dewpoints.  I’ve marked it in red to show my own heat-averse opinion.  (Click on the screenshot to see their dewpoint video that includes this chart.)

So here’s what was really going on this week and why it felt so hot yesterday even though the temperature never reached 90 degrees.  Notice that the relative humidity was at its lowest yesterday afternoon.

Find out the dewpoint before you go outdoors and you’ll know whether you want to brave it!

(*) p.s. See the comments!

(video from Richard Clements on YouTube. screenshot from NWS Chicago video. Click on the screenshot to see the video)

June 20, 2016:

Today is astronomical.  It’s been 68 years since we’ve seen one like it.

The last time the summer solstice occurred on the same day as the full moon was in 1948.

By the time you read this the moon will have done its job, having reached maximum fullness at 7:05am in Pittsburgh.  It had already set by then (6:13am) so we didn’t see it.

The summer solstice is yet to come — 11.5 hours after the moon’s event — at 6:34pm.

The moment when the sun stands still is such a big deal that they’re celebrating it with a four-day solstice festival at Stonehenge, pictured above.  But they won’t be able to see the sun during its special moment.  It’ll be almost midnight at Stonehenge, 11:34 pm.

Read more about this astronomical event at the Old Farmer’s Almanac.

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

Today we get the gift of time.  Leap Day, February 29, gives us 24 hours that are usually missing from our calendars.

You probably know we have to insert this day every four years because the earth revolves around the sun in approximately 365.25 days.  To make the calendar match the stars and seasons we add an extra day every fourth year with a complicated century exception.  The 4-year-old video above explains the details of this astronomical problem and how Julius Caesar and Pope Gregory XIII figure into it.

Last June 30 we received the gift of an extra second.  You probably missed it because it happened just before midnight.

Leap Years and Leap Seconds are unrelated but caused by a similar problem. Just as calendars must adjust for Earth’s rotation, so too must atomic clocks. The clocks are extremely accurate but Earth’s rotation is slowing down and not even at a consistent rate.  An extra second is added whenever the difference between mean solar time (UT1) and Coordinated Universal Time (UTC) reaches 0.9 seconds.  The need for this second is so unpredictable that it’s announced only six months in advance.  Computers hate this but there are workarounds.

In the past eight months we’ve gained 24 hours (on February 29, 2016) + 1 second (on June 30, 2015) + 1 hour (changed to Standard Time on November 1, 2015).  This nets us 25 hours + 1 second.

Do something fun with the gift of time.  Happy Leap Day!

p.s. We’ll lose an hour in two weeks on Sunday March 13 when we switch to Daylight Savings Time.  Yikes!

(Leap year video by Epipheo on YouTube. Leap second illustration from Wikimedia Commons; click on the image to see the original)

8 February 2016

Science Fun:

John English told me about this cool website that animates global weather, especially wind on water.  The website is called earth, “a visualization of global weather conditions forecast by supercomputers updated every three hours.”

Click on the screenshot above to see conditions in the eastern North Pacific. Before you do, here are some tips:

• In the animation, slow winds are blue to green, intense winds are orange to red.
• Everywhere on earth, the most exciting winds are those surrounding low pressure systems.  In the northern hemisphere, they circle counter-clockwise. (How to remember this? See below.)
• Notice the blank zones where there’s no wind. The largest are often in the center of high pressure zones.  Some of these line up with the warm water “Blobs” that are killing seabirds by starvation.
• If you watch for 60 seconds more winds on the continent will start to show up. They aren’t as intense.
• Click and drag to change the location of the map.
• Click on the word [earth] at bottom left to change the parameters.  Select a new Mode to see pollution (“chem”) or dust/smoke (“particulate”).

Follow this quick link to see the North Atlantic and Great Lakes map.  There’s usually less excitement here but look north toward Greenland and you’ll see why the North Atlantic is a dangerous place to cross in winter.

And for a really tangled mess of wind click here to see the air flow between South America and Antarctica!

Visit “earth” on Facebook for more screenshots and videos of amazing storms.  You don’t need a Facebook login; just click on the link.

BONUS: Here’s how to identify low and high pressure systems in the northern hemisphere based on the direction the winds are circling. Use the right-hand rule. Curl your fingers in the direction of the winds (B) and point your thumb. The air column (I) is moving in the direction of your thumb. Low pressure sucks the air column up; high pressure pushes it down. The orientation of this diagram would be a low pressure system in the northern hemisphere.

(screenshot of the earth wind map from earth.nullschool.net, right-hand rule illustration from Wikipedia)

In case you didn’t hear this on the news last week … you’ll be interested to know that between January 20 and February 20 you can see all five visible planets 80 minutes before sunrise in an arch across the southern sky.  That’s Mercury, Venus, Saturn, Mars and Jupiter in order left to right.

The illustration above, linked from earthsky.org, shows where to look and when.  Click here or on the illustration to read more about this phenomenon.

Sunrise tomorrow, Monday, January 25, is at 7:35am in Pittsburgh, but before you set your alarm so you can be outdoors facing south by 6:15am you’ll want to know if it’s worth it. Pittsburgh’s skies are notoriously cloudy in the winter.  Will the sky be clear enough to see five planets?

To find out, check the handy chart for Pittsburgh here at ClearDarkSky.com.

Here’s a sample of what you’ll find when you get there.  This is yesterday’s chart surrounded by an orange border to remind you that this is ONLY A SAMPLE! Click on the image to see the real thing.

On the chart, dark blue on the “Darkness” line is good.  The white to pale blue areas indicate cloud cover, moonlight or sunlight.

Check the chart and get up early between now and February 20.

If you don’t live in Pittsburgh, click here to find your location.

Good luck!

(illustration of five planets linked from EarthSky.org plus a sample of the Pittsburgh Clear Dark Sky chart from ClearDarkSky.com)

If you’ve been paying close attention, you may have noticed that most media about this weekend’s weather calls it “the storm.”   It does not have a name. But if you tune into The Weather Channel, they call it Jonas.

In October 2012 The Weather Channel announced they would name winter storms to improve their communications about the storms.  This was not a popular move.

Within a month the National Weather Service announced they would not use the names. By February 2013 Accuweather, the New York Times, the Washington Post and others went on record that they wouldn’t use them either.

That’s why, three+ years later, only those who watch The Weather Channel call this storm by name.

(screenshot from The Weather Channel. Click on the image to see the news article at TWC)

p.s. On a personal note, I get my weather from the organization that provides the data (in the public domain & mostly free of charge!) that The Weather Channel uses to make their forecasts:  The National Weather Service

Coming this month is the lecture I’ve been waiting for.  On January 27 I’ll learn how NASA finds water using satellites instead of this old method of dowsing with a forked stick.

Since 2002 NASA’s paired GRACE satellites have been circling the globe measuring Earth’s gravitational pull.  What they’ve also discovered is a way to measure groundwater.

How do they do it?  Learn more here in my January 2014 blog post:  Dowsing From Outer Space.

Want to know more?

Come to the University of Pittsburgh Honors College lecture entitled:

Monitoring Groundwater Variability from Space

by Dr. Matthew Rodell, Chief, Hydrological Sciences Laboratory, NASA Goddard Spaceflight Center

When:  January 27, 2016,  4:00 PM

Where:  Alumni Hall, Connolly Ballroom, 4227 Fifth Ave

The lecture is free and open to the public but space is limited. Click here for more information and to reserve your seat.

(photo of George Casely dowsing on his farm from Wikimedia Commons. Click on the image to see the originals)