Thursday, June 28, 2012


The constellation Libra is up in the sky after dark... but where? 

It's a small constellation with mostly dim stars so it's hard to find.  The easiest way to do it is to find the zodiac constellations that are bracketing it: Virgo the Maiden on its right, and Scorpius the Scorpion on its left.

Virgo is recognizable by her bright blue star called Spica.  Spica is below a yellow "star" of similar brightness.  That star is really the planet Saturn.  Maybe Virgo is like Lady Justice holding the nearby scales?  She must have some good balance because Libra is at her feet!

Libra and Scorpius have a long history.  In fact, the two brightest stars in Libra (Zubenegenubi and Zubeneschemali) mean the "Claws of the Scorpion."  And it makes sense since the Scorpion's head, heart, body, and stinger are in the stars.  Why not some claws?  Plus I like to say "Zubenelgenubi," and Zubeneschemali!" 

Libra is the only non-living thing in the zodiac.  Since the zodiac means, "Ring of Animals," it definitely stands out.  Try to find the scales tonight in the southern sky after dark.

Wednesday, June 20, 2012


Today, June 20 is the Summer Solstice which means that the Sun appears the farthest north for the year.  You know how the Earth is tilted 23.5 degrees?  Well, the northern hemisphere is tilted most directly at the Sun today and we're soaking up solar energy to the max. 

But we are we tilted 23.5 degrees to?  It's two factors - our daily rotation on our axis, and our year revolution around the Sun.  Our axis is tilted 23.5 degrees to the plane of our orbit - the path we take around the Sun.  So our entire Earth spins a little on our side as we orbit the Sun. 

BTW, the word solstice means, "Sun Standing Still."  Now that doesn't mean that the Sun stops for a second or two.  Our ancestors noticed that on a few days in the summer and a few days in winter that the Sun rose from the same spot in the northeast and set over the same spot in the northwest.  Other times of year, they could see the Sun rise and set in slightly different places each day.  But not on the solstices!  So it's the Sun's Path that stands still for several days, not the Sun.  Civilizations around the world  marked these special days with monuments that tried to capture those rising and setting sun rays like at Stonehenge, Serpent Mound, Fort Ancient, and Chaco Canyon.

Go check it yourself.  See where the Sun rises and sets over the next few days and you'll see what I mean.

Wednesday, June 13, 2012


Thoughts on a Twice in a Lifetime Event

Tuesday’s Transit of Venus was the last time I will see the beautiful planet cross in front of the face of the Sun. I already miss her.

Sure I’ll be able to see Venus again in only a few short days as she pops out into the pre-dawn skies but she won’t be the same. A Transit of Venus has transformed her. This rarest of astronomical events changes your perspective not only the planets but the history of the universe.

A Transit of Venus only occurs when the planet Venus comes directly between the Earth and Sun. Much more subtle than a solar eclipse, the Transit of Venus is unique because of its precision, its history, and its rarity. The Sun, with Venus as a small beauty mark marching slowly across its behemoth face, has been noted just seven times in human history.

For the Transits of the 1700s and 1800s, astronomers sailed around the world to catch a glimpse of it. In 2004 I drove my Geo Metro to New Hampshire to see it over the Atlantic Ocean at sunrise. And on Tuesday I flew on a Delta jet to Arizona to witness the event over the stark, high desert. Millions of people watched the various Transit webcasts from around the world. My journeys in 2004 and 2012 and those virtual journeys would have been unthinkable to those viewing the Transit of 1882.

After the Transit of 1882, the last one prior to 2004, an editorial ran in the New York Times musing about the future when “the June flowers are blooming in 2004.” It said, “When the last transit season occurred the intellectual world was awakening from the slumber of ages and that wondrous scientific activity which led to our present advanced knowledge was just beginning. What will be the state of science when the next transit season arrives God only knows.”

Our scientific knowledge in astronomy progresses so rapidly that discoveries are made daily. The next Transit of Venus won’t be until the year 2117 and even that one won’t be visible from Cincinnati. Our ancestors will have to travel to Asia, Australia, or Africa to see it. How will they get there? What will life be like 105 years from now? In the 22nd century will space tourists watch Transits of Venus far above the Earth any day they choose?

Even as an astronomer it’s hard to wrap my mind around distances, cycles, and expanses of time that are, well, astronomical. But I am reassured that no matter what may happen on Earth, the Transit of Venus will occur again on December 10, 2117 and December 8, 2125. To those witnessing the next pair of Transits in the 22nd century under the December Sun, in a future I can’t begin to imagine, I wish you clear skies and the same spectacular view that we had twice in the 21st century.

Thursday, June 7, 2012


On the morning of June 4, 2012 there was a partial lunar eclipse only visible in the western United States.  As chance would happen, I was visiting Flagstaff, Arizona in route to see the Transit of Venus the very next day.  What an added bonus to be able to see a lunar eclipse followed by a Transit of Venus all within a 36-hour span!

I took some pictures of the eclipse and it got me thinking...  Whenever I teach students about the Moon phases I try to demonstrate that they are not caused by the shadow of the Earth.  The Earth casts a round shadow on the Moon so how could it make a gibbous Moon?  It's impossible - the dark part is curved the wrong way.  In fact when I ask students to draw a gibbous Moon and they give me an eclipsed Moon - ouch, I give them double-points off! 

Below I have a normal gibbous Moon on the left and the eclipsed Moon on the left.  Notice the difference?  Right click on the picture and open it in a new window for a close-up view.

Gibbous Moon                   and                   Partial Lunar Eclipse