Star Struck


Over the next 16 months, the data collected during the New Horizons spacecraft’s mid-July flyby of Pluto will find its way back to Earth, a few bits at a time. Already there are surprises in the data so far received. How could there not be? We are seeing a whole new world revealed in detail for the first time in human history. The analyses and debates will surely only have begun once all the data are in.
The image below on the left is from the Hubble Space Telescope, and until July 2015 it was the best we had. The true-color image on the right is from the New Horizons flyby.
Pluto before and afterI thought it might be useful to write on what we have learned about the small icy worlds of the solar system from our previous explorations. Perhaps a more appropriately humble description would be that this is what we think we know! Each new world forces us to re-examine our assumptions, each new question begets ten more. Such is the nature of science, and the source of its endless fascination for so many of us.
Worlds of Rock, Gas, and Ice
Leaving out a lot of detail, we can think of solar system bodies as being composed of rock, gas, ice, or some combination thereof. The four innermost planets (Mercury, Venus, Earth, and Mars) are relatively small and rocky, and the four outermost (Jupiter, Saturn, Uranus, and Neptune) are mostly gaseous, with ice becoming more prominent as we reach the more distant environs of Uranus and Neptune.
800px-Size_planets_comparisonAmong the inner planets, Mars has two tiny rocky moons that may be captured asteroids, and the Earth has a rocky moon that is likely the result of a massive collision early in its history. Neither Mercury nor Venus has a moon.
The inner solar system has numerous smaller bodies collectively called asteroids that are mostly rocky. The greatest numbers of these lie between Mars and Jupiter, or co-orbiting ahead of and behind Jupiter in its orbit. Icy bodies wander into the inner solar system from farther out, spewing gas and dust tails as they are warmed by the sun. These are the comets that periodically grace our skies.

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The Great Age of Planetary Exploration

How do you measure the milestones in your life? We all have events that help us mark the passage of years: school and jobs, marriage and family, births and deaths. These are of course primary in all our lives, but the recent encounter of the New Horizons spacecraft with the Pluto system has reminded me of the very special period of time that my own life has spanned. In the last 65 years, we have slipped the bonds of gravity that held us to the Earth and completed a survey of our solar system. Nothing comparable has happened since the great age of Earth’s exploration begun 500 years ago; nothing comparable is likely to happen for decades or centuries to come.

I was barely three weeks old when the first rocket was launched from Cape Canaveral, Florida in July 1950.

July 1950 Cape Canaveral
I was fifteen years old and completely obsessed with space when Mariner 4 flew by Mars in July 1965 and sent back the very first pictures of another planet.
Mars had no canals! Instead, it had moon-like craters and a disappointingly desolate appearance. As it turned out, Mariner 4’s flyby path took it over some of the least interesting of Mars’ topography. It fell to Mariner 9, which settled into orbit around the planet late in 1971 and patiently waited while global dust storms abated, to discover the solar system’s largest (extinct) volcano and a chasm that could swallow Earth’s Grand Canyon in one gulp.

But perhaps the greatest planetary explorers of all time were the twin Voyager spacecraft launched in 1977. Both Voyager 1 and Voyager 2 explored Jupiter and Saturn and their moons, while Voyager 2 was directed on to Uranus and Neptune. The images that the latter craft took of these giant planets are the only close-ups we are likely to see in our lifetimes.

And now, 50 years to the day after those first grainy black-and-white images from Mars that so astounded us, we have our first images of Pluto, taking four and a half hours to travel over 3 billion miles, and providing our first clues to new mysteries of planetary formation that await us.

It is a remarkable time to be alive. I can’t help but wonder what it must have been like for people greeting Captain Cook and Joseph Banks on the English docks in 1771 as they returned with stories of exotic Pacific Islands and hundreds of miles long coral reefs. How their world must have been enlarged by this new knowledge!

The world is much larger than our own dust mote of a planet, larger even than the system of planets that circles our life-giving star. But we have completed an important first round of exploration of the vastness that surrounds us.

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Nine Years to the Ninth Planet

Yes, you read that right. In honor of Pluto’s imminent debut on computer screens worldwide, I’ll award it planetary status for the next few months. After all, when the New Horizons spacecraft nearing Pluto now was launched in January 2006, the (in)famous demotion to dwarf planet had not yet occurred.

If you are an aficionado of rocket launches, you will note that the New Horizons booster rocket fairly leaped off the launch pad. In fact, this spacecraft left the Earth faster than any other in history, passing the moon’s orbit in nine hours and reaching its encounter with Jupiter in less than fourteen months.

The Jupiter fly-by not only redirected New Horizons’ trajectory, it sped the spacecraft up by “stealing” a little energy from the massive planet in what is sometimes called a gravity assist maneuver. The mass differential between the spacecraft and the planet means that Jupiter will never miss that stolen energy. Without this maneuver, it would have taken even longer to reach this outer region of our solar system.
So why was every third-grader’s favorite planet demoted, anyway? Rather than the last planetary outpost, Pluto is better regarded as the threshold of a different region, the Kuiper Belt. These are icy remnants of the primordial solar system, so distant and small that their very existence was not confirmed until 1992. As more and more of them were discovered, the realization dawned that Pluto was just the nearest and one of the largest of these objects. Their remoteness makes knowledge of their detailed nature not much beyond speculation. But Pluto is about to help us better understand what they are about. As unaltered specimens dating to the very earliest days of the solar system, they should help us better understand how it evolved over its 4.5 billion year history.
Closest approach to Pluto is at 7:50 am EDT on Tuesday, July 14th. It will take some time to transmit all the data collected back to Earth. Pluto is so distant that it takes the radio signal four and a half hours to reach us. The spacecraft will be busy as it whizzes by at almost nine miles a second.

The time given are UTC (Universal Coordinated Time) on July 14th; Eastern Daylight Time is four hours earlier.
And finally, here are the latest (as of July 2nd) pictures of Pluto and its largest moon Charon, each showing a different hemisphere of Pluto. These will quickly be outdated as an entire new world is unveiled for the first time in all human history.

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Venus, Jupiter…and Earth

Those of us of a certain age will remember these song lyrics:

When the moon is in the seventh house
And Jupiter aligns with Mars…

Jupiter is about to align not with Mars, but with Venus, the ancient goddess of love. We can only hope that peace will guide the planets as a result!

The commonly used term for this is a conjunction, when two celestial objects appear very near each other in the sky. Strictly speaking, this is incorrect; the astronomical term applies to two objects that share only one of the two dimensions used to map objects onto the sky. Imagine Memphis and New Orleans. They share the same longitude (roughly 90 degrees west), but Memphis lies about 5 degrees of latitude north of the Big Easy. We won’t split hairs here, however.
Here is a series of screen shots showing how the two planets will move ever closer to each other over the next few nights. Each of these shows the view from Lynchburg, Virginia at 9:00 PM EDT.

Venus Jupiter Conjunction
The exact moment of closest approach is at 10:55 PM EDT on June 30.

Their proximity is only apparent, however, not real. I can line up my finger with a distant mountain peak without having climbed the mountain! This view from above the plane of the solar system illustrates the point.

Venus Jupiter Conjunction Overhead
Enjoy the view! If you forget which of the two planets is which, Venus is by far the brighter of the two.


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Astronomy and Me

This post is not informational so much as it is a personal reflection on what astronomy has meant in my life. Our regularly scheduled programming will resume in the next post.

One of my very earliest memories comes from shortly after my fourth birthday, when my great-grandmother let me stay up late to watch a summer meteor shower. I have vivid images in my head of flaming boulders tumbling through the sky. Of course real meteor showers look nothing like that; my memories were surely shaped by what I was told about what I was seeing. Most people of my age who were interested in space point to the launch of Sputnik as the spark that lit that fire. But I was telling people I wanted to go to the moon two years before Sputnik, and I have always thought it was that night in August watching streaks of fire cross the sky that inspired me.

For many years I was an armchair astronomer, someone who only reads about it, who could tell you the names of the then-known planetary moons (so few compared to now!), could describe interplanetary transfer orbits, and could drone on about galactic classification. Somewhere along the way I let the magic of that August night, of what the wonder of that natural phenomenon felt like—somewhere that got lost. I think that sort of appreciation requires a patience that is not typical of young people in a hurry. At least it was not a prominent feature of my youthful make-up.

But one night in my back yard with a new telescope, I encountered the mystery and the awe, the numinous experience of seeing light that had traveled for 25,000 years just to be focused into my eye. The combination of light pollution, my initial lack of dark adaptation, and the relatively small size of my instrument meant that all I could see at first was a tight ball of stars. Gradually, more and more stars began to appear, as the shape and stellar distribution of M13, the Great Hercules Globular Cluster revealed itself.


Suddenly—and this is a trick of vision and of the mind—it was as though someone had flipped a switch, and the view became three-dimensional. It was as though I was falling head-first into a field of stars. I actually gasped and stepped away from the eyepiece.

I was hooked.

Why stand under a dark night sky, and why look through a telescope of any size, when spectacular images of every sort of astronomical wonder are only a few mouse clicks away? Here is my answer, several of them actually. First, it teaches us that appearances can be deceiving. It’s really not at all obvious that the stars are more than a few miles over our heads. And these points of light that are extinguished by the daytime sun? In reality they are vast nuclear furnaces dimmed only by equally vast distances. Second, it teaches us humility. It is difficult to maintain arrogance in the face of stretches of empty space where the earth is a dust mote, and where objects that are just middle-aged are hundreds of millions of times older than an elderly human. Lastly, it teaches us to truly see instead of just looking. A quick glance at a galaxy will surely show something. But the sweep of spiral arms, the subtle patterns of dust lanes in those arms, the clustering stars in the central hub, the companion galaxy, the streamer of stars bridging the two, the subtle shape distortion caused by their interaction—all these require the patience of the person who sees and does not just look.


Humility in the face of the time and distance scales of the universe is certainly appropriate. It need not, however, lead to despair. In all this emptiness, there is an uncharacteristically rich collection of matter in one little corner of the universe, where matter is sufficiently organized to contemplate questions of origin and place. We have discovered other places where that may be possible, but that is all we can say with any certainty. So far as we know, there may be no other such place than our Earth.

We are small and we have but a few short years in all this vastness. But perhaps we are not so insignificant after all.


Posted in Sky Phenomena

Cute Little CubeSats

What do this

Questar Telescope
and this

Dove Satellite
have in common?

The first picture is of Lynchburg College’s 3.5-inch Questar telescope, a gift to the college from a long-time Board of Trustees member. For those who don’t know, Questar is to small telescopes as Mercedes-Benz is to automobiles: beautifully made, and they last forever. This one was manufactured in 1963.

The second picture is of a Dove CubeSat, manufactured by Planet Labs. CubeSats are designed to be a cheap way to get something into space. A 1U (one unit) CubeSat is ten centimeters on a side with a mass limit of one kilogram—the size and mass of one liter of water. The Dove is a 3U CubeSat, 10 x 10 x 34 centimeters.

What these two images have in common is the Questar telescope, although the one in the Dove is made of Invar, an iron-nickel alloy notable for its resistance to thermal expansion. This is especially important in the space environment, where instruments are alternately baked and frozen. The Lynchburg College instrument is made largely of aluminum.

The remarkably small size of this satellite is testimony to the huge advances in consumer electronics over the past twenty years. Most of its components are off the shelf: the electronics are essentially those of a smart phone and of a radio transmitter and receiver. The telescope has a high-resolution CCD camera at its focus, and the images it captures can be sent back to a relatively small radio dish on Earth. The picture below is of strawberry fields in Florida. Beatles fans will know why I picked this image.

florida-strawberries from dove satellite
You can view a gallery of such images here.

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New Horizons Update

As the New Horizons spacecraft closes in on its July flyby of Pluto, its cameras capture ever higher resolution images.  Here is a link to the latest released images.  It’s starting to get real!


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A Cosmic Dance

The two brightest planets in the sky right now—and the two brightest planets, period—are Venus and Jupiter. Shortly after sunset at the end of April, Venus is the very bright object in the west, and Jupiter is only a little less bright high in the southern sky. In actual fact, they never get very close to each other. Venus orbits closer to the sun than does Earth, and Jupiter much farther from it. At their closest, Venus and Jupiter are well over 400 million miles apart: four and a half times the distance between the Earth and the sun.

But if astronomy teaches us anything, it is that what you see very much depends on where you stand. From our vantage point on Earth, Venus and Jupiter sometimes appear to be quite close to each other. And at the end of June, they will be less than half a degree apart, less than the width of a full moon. Such an apparent meeting of two celestial bodies is called a conjunction.  Here is a view of the sky at 9 pm tonight (April 24, 2015) as seen from Lynchburg, Virginia.

Venus Jupiter April 1

When we look at the sky, it’s easy to see how our ancestors imagined it as a bowl, with all the celestial objects about the same distance away from us. In fact, it has enormous depth, with some objects like the moon quite close, and others like Jupiter much farther away. Its three-dimensional nature is not readily apparent.

If we take a different perspective—if we stand in a different place—we can see how two objects that appear to be close together do so only because they lie along the same line of sight. Here is a view from above the solar system. In this view, the Earth’s north pole is directly below us, and all the planets orbit the sun in a counter-clockwise direction.

Venus Jupiter April 2
At the end of April 2015, Venus and Jupiter lie in different directions as viewed from the Earth. But as the planets orbit the sun, those nearer the sun move faster. Venus closes on the Earth as the weeks pass, and at the end of June it is much nearer to us. The more distant Jupiter meanwhile has moved only a little along its nearly twelve year long path.

Venus Jupiter Conjunction 2
On the evening of June 30/July 1, the two will be at their closest approach, less than the width of your finger held at arm’s length.

Venus Jupiter Conjunction 1
The weeks leading to that night will be rewarding as well, as we watch the two brightest natural sky objects after the sun and the moon approach each other in a cosmic dance, and as we remind ourselves that a different location in the solar system would provide a very different view.


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Ceres Awaits

Dawn is sneaking up on Ceres from behind.

On March 6, this well-traveled spacecraft slipped into orbit around the dwarf planet (or asteroid; take your pick) after having spent 14 months orbiting the asteroid Vesta and more than two years in transit to Ceres. But Dawn’s approach to Ceres is from its unlit side. Pictures taken on the approach to orbit revealed two bright spots that have scientists intrigued as to their nature. The best guess is water ice, but the details await higher-resolution images.

In this diagram below of the approach to Ceres, the view is from the side, with Ceres’ north pole at the top of its disc, and the sun to its left. I’ve darkened the unlit side of Ceres to make this more obvious. Dawn’s current (April 18) approximate position is marked by the yellow X. The white circles mark one day intervals along the path.

You can see that for the last several weeks, Dawn has had only Ceres’ dark side in view. Once the spacecraft is in its initial science orbit, it will be able to see the entire surface as it rotates beneath. But we finally have some images released of the sunlit north pole of Ceres. Enjoy this animation as we await the unveiling of yet another previously unexplored solar system body!



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Getting to Pluto

What were you doing on January 19, 2006? If you were in any way connected to the New Horizons mission to Pluto, you were at the Kennedy Space Center in Florida to watch it being launched on its long journey. I chose this video for the audible reactions of the onlookers as much as anything. A rocket launch is a thrilling event!

When New Horizons began its journey, Pluto had not yet been demoted to “dwarf planet” status. Still, for most people, it marks the outer boundary of our solar system, the farthest outpost on the way to the stars. Getting there requires a very fast ship.

Getting anywhere in space is always a trade-off between how fast you can get there and how big a payload you can transport. A limiting factor for both is how big a velocity boost you give your mission at the outset. Once most interplanetary missions have achieved orbit around the Earth, they use very powerful chemical rocket engines that burn for a matter of minutes but change the spacecraft’s velocity significantly. (There are exceptions; see this article about the Dawn spacecraft.) They then coast for months or years on the way to their destination. The resulting trajectory is a long and curving one, as planets and spacecraft all orbit the sun. For example, this is the path taken by the Curiosity rover spacecraft to Mars:

So how do you get to Pluto?

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