Happy Birthday, Carl

(Originally posted on Maddow Blog, 9 November 2011)



Thirty-four years ago, NASA launched the Voyager 1 space probe as part of a Planetary Grand Tour proposed by scientists at the Jet Propulsion Laboratory. The plan was to use the technique of gravity assists to exploit an alignment of the outer planets that would allow for a single probe to visit Jupiter, Saturn, Uranus, Neptune, and Pluto using the encounter with each planet to slingshot it on a trajectory to the next.

The Grand Tour was eventually cut back, and Voyager 1 only visited Jupiter and Saturn before heading to the outer reaches of the Solar System and eventually interstellar space. The design life of the probe was approximately three to four years, just long enough to complete its primary mission, but once it became clear it would continue to function for some time to come, Carl Sagan proposed the turning the spacecraft around to take a last look at Earth. His purpose was more philosophical than scientific; no one had ever seen Earth from such a great distance before. He was more interested in the perspective such an image might provide to a species that had, for the most part, never been away from home.

In the spring of 1990, Voyager 1 sent a series of images back to Earth, one of which we now know as the indelible portrait of our planet from over 3.5 billion miles away. In honor of Carl Sagan's birthday, I thought it appropriate to revisit this unique view of all that we know in this Universe, all that we call home, the only home we've ever known.

Maddow Blog

I haven't posted here in a while for several reasons, one of which is that I've occasionally be writing posts for The Rachel Maddow Show over on Maddow Blog. But in the interest of alerting those of you that may only follow me here, I'm going to start cross-posting. Just wanted to let you know!

Godspeed

I've been obsessed with space ever since I first looked up at the night sky. My mom even has me on tape at 18 months or so trying to talk about the moon.

So as the space shuttle program comes to a close this month, I (along with many others) have been reflecting back on what it's meant to me. Essentially, the shuttle program and I have grown up together. It's been a major influence in my life and what I've chosen to do. Regardless of any political, economical, or even scientific arguments on the practicality of manned spaceflight, the sheer power of inspiration cannot be ignored.

I grew up just outside of Washington, D.C. and was lucky enough to be able to go to the National Air & Space Museum almost whenever I wanted. In 1985, my mom took me there to see The Dream is Alive, the IMAX film on the shuttle program, which was still in its infancy. If I had any doubt that I wanted to go to space before then, that film obliterated it. I can still close my eyes and replay it in my mind. I can hear the sonic booms at the start, retrace the camera sequence over the beach and marshes to the shuttle on the launch pad, and jump despite myself when the astronauts practice their emergency egress from the cockpit and zip down the escape lines.

I won't bore you with every space shuttle related memory I have (we would be here all day), but I'd like to mention someone who went out of his way to help me pursue my own space dreams. After college, I went to work at Orbital Space Sciences Corporation, in Dulles, VA on the X-34 Reusable Launch Vehicle Program. Somewhere in my first year, we got a new program director: ex-astronaut G. David Low. David was not what you immediately think of when picturing an astronaut; he was relatively small in stature and quiet in nature, not at all the outgoing fly-boy stereotype. I can still remember our first all-staff meeting in the high-bay where I had to strain to even hear him. Soon enough though, I got to experience what an amazing leader and mentor he could be.

One weekend when we were all working through a program review, I was grabbing a slice of pizza in the conference room and David mentioned to me that he had heard I wanted to be an astronaut. I never in a million years would have walked up to him and asked for advice, that's just the way I was at the time, but here he was actively volunteering to answer any questions and do what he could to help. In the summer of 2001, he helped me plan a trip to Johnson Space Center to meet with the head of the astronaut office and some of his former colleagues who were still active in the astronaut corps. Every single person I met welcomed me with open arms and spoke fondly of working with David. When I finally did apply to be an astronaut, David jumped at the chance to provide a reference.

I left Orbital to go back to school in the fall of 2001, but I frequently went back to visit my colleagues (most of whom are now good friends) and I always made a point of stopping in to see David. He had a way of making me feel full of potential, like I could do anything I set my mind to. He made everyone around him better. I'm speaking in the past tense because David passed away in March of 2008 due to colon cancer. I still miss him greatly and often come across things I wish I could share with him. I would love hear his perspective on the future of manned spaceflight given the crossroads we are currently at. I know he would say this is not the end, just a hiatus of sorts.

I like to think the same of my time with David. It didn't end when he died, it just got disrupted. He led and inspired others by example; something he and the space shuttle program have in common. Both have played important roles in my life and have made me who I am today. And I will carry both of them in my heart and my mind as I step into the future.

Godspeed G. David Low, wherever you are, and godspeed Atlantis.

Eratosthenes' Shadow

Some days the world feels really big and somedays it feels quite small, but as you might suspect, it doesn't actually change size. Here in the 21st century, we know the circumference, density, and other physical properties with great accuracy. However, back in 3 BC even the first of these was still a mystery. That is, until a man named Eratosthenes devised a simple yet elegant way to calculate the size of the Earth using nothing but the Sun and some mad geometry skills.

My friend, Gene Gordon, a high school physics teacher in upstate New York got me excited about the simplicity of Eratosthenes' original experiment. Gene had the great idea to use social media to get students all over the country (and even the world) to recreate Eratosthenes' experiment "simultaneously."

I'm going to let the one and only Carl Sagan give you the full background on Eratosthenes farther down the post, but in the spirit of Gene's lesson plan, I want to demonstrate how you too can determine the size of the Earth with a little help from your friends.

Now comes the math. I promise it won't hurt.

1) Calculate the angle the sun's rays hit your stick at solar noon using the equation given below. You and your friend should each do this separately. This will give you TWO ANGLES, one for the person at the higher latitude location and one for the person at the lower latitude location. [Hint: the function below is called "arctan" and appears on any scientific calculator.]

2) Whichever one of you has the smaller angle, subtract this from the bigger one. This is your THETA.

3) Find the distance in miles or kilometers between the LATITUDE of your location and the LATITUDE of your friend's location. (DO NOT find the distance as the crow flies.) This is your DISTANCE.


4) Now for the grand finale! Your THETA represents a portion of a full circle, a fraction of 360 degrees. Your DISTANCE is the equivalent fraction of the Earth's circumference. So divide your THETA by 360 and multiply by your DISTANCE. TA-DA! You've calculated the circumference of the Earth. [Note: your circumference will be in the same units as your stick and shadow so a little unit conversion may be in order.]


Eratosthenes actually had it easy, he already knew of a nearby city (Syene) where the Sun was directly overhead at midday on one day of the year - the summer solstice - meaning that all he had to do was measure the angle of the Sun in Alexandria, where he was.



Because the Sun is so far away from Earth, incoming light rays are essentially parallel. And thanks to geometry, we have a handy-dandy theorem for determining angles when two parallel lines are transected by a third line: alternate interior angles are congruent (or equal). In practical terms, this means that the angle measured by Eratosthenes in Alexandria is equal to the angular distance between Alexandria and Syene. To get the last piece of the puzzle, Eratosthenes paid a guy to actually pace out the distance between the two cities. E voila! He had all he needed to calculate the circumference of the Earth. And he was surprisingly accurate, coming well within 10% of the present day value of ~40,000 km (depending on historical interpretations).

But enough math for now! I'll leave you with how Carl tells the story of Eratosthenes, which is of course beautifully.

Mercurial Musings

For the first time since 1975, a manmade spacecraft is surveying the innermost planet of our Solar System.

MESSENGER, which stands for "MErcury Surface, Space ENvironment, GEochemistry, and Ranging," left Earth's surface back in 2004 and took the long way round the inner Solar System before reaching its final destination on March 17th, 2011. And when I say "long," I mean 4.9 billion miles long. The full route consists of multiple flybys of Earth, Venus, and Mercury itself, as visualized in this animation. (For a more detailed discussion of gravitational assists, see my previous post on MESSENGER here.)

Now, almost eight years later, MESSENGER has settled into its new home and will begin taking data next week. The spacecraft's primary mission is to look for answers to such questions as: Why is Mercury so dense? What is the nature of Mercury's magnetic field? And what is the structure of Mercury's core?

Of the terrestrial planets in our Solar System, Mercury is by far the smallest and densest. Its surface is extremely old and undergoes daily temperature swings of over 1000 degrees. And its also the least explored. The better we can understand how Mercury formed and evolved, the better we can understand the conditions during the formation of our Solar System -- and our Earth.

Designing, building, and operating MESSENGER is no small feat. Neither is launching a sophisticated chunk of electronics into space and maneuvering it through the solar neighborhood. The scientists and engineers who got it there deserved to be celebrated. As does our desire to explore.

(Image credit: http://www.nasa.gov/mission_pages/messenger/main/index.html)

Remembrance of Things Past

Today is the day NASA sets aside to remember those who gave their lives in pursuit of our dreams to explore above and beyond the surface of our planet.

January 27, 1967 - the Apollo 1 space capsule was engulfed in flames during a pre-launch test.

January 28, 1986 - the Space Shuttle Challenger exploded less than a minute and a half after launch.

February 1, 2003 - the Space Shuttle Columbia broke up upon re-entry.

While I wasn't alive during the Apollo program, I am old enough to remember exact where I was during both the Challenger and Columbia disasters. They both affected me deeply.

I have been in love with the Universe for as long as I can remember. I'm pretty sure it was a done deal when I first saw the Moon in the night sky. My mom can attest to that. Be it movie, book, or museum, I devoured all things space related. And while I've come out the other side of my astronaut phase (for various reasons), I would still gladly sit on top of a rocket, no matter what the risks, to have the chance to touch the stars. And I know each of the astronauts who lost their lives in these disasters felt the same.

So I'm glad NASA has established this day of remembrance to honor both the sacrifice that comes with exploration and the dreams that drives us to explore in the first place. Ad astra per aspera.

Happy New Anomalistic Year!

Time to pop the champagne again if you like to celebrate extremes. Today the Earth is at the point in its orbit closest to the Sun. Astronomers call it "perihelion," a description derived from the generic term for the point of greatest or least distance of a body from one of the foci in its elliptical orbit: apsis.

Johannes Kepler was the first to realize that the planets orbited the Sun in elliptical, rather than circular, orbits. This was radical at the time, because the heavens were considered divine and flawless; for the planets to orbit the Sun in non-circular orbits was tantamount to heresy. Yet, the detailed observations of Tycho Brahe that Kepler based his work on showed this to be the case.

Instead of a single center, like a circle, an ellipse has two centers, known as foci (plural for focus). When two celestial bodies are orbiting each other, they both move in elliptical orbits about a common center of mass where the gravitation force between them is balanced. This occurs at one of the foci. You can think of it like a seesaw where the center of mass is the fulcrum point where the seesaw balances. If two people of equal mass sat on a seesaw together, the balance point would be halfway between them. However, if one person greatly outweighed the other, the balance point would have to be moved much closer to the heavier individual. The center of mass between two celestial bodies is just the same. The mass of the Sun is about a million times more than the mass of the Earth, therefore the center of mass between the Sun and the Earth is greatly skewed towards the Sun.

Earth's elliptical orbit is characterized by an eccentricity of approximately 0.018. Eccentricity is defined as deviation from a perfect circle, where 0 is a perfectly circular orbit and 1 is a parabola, essentially a broken circle that is no longer a closed loop. Earth's orbital eccentricity actually varies from more circular (0.005) to somewhat elliptical (0.058) due to the gravitational interactions in the Solar System, but that's a post for another day.

(Figure so not drawn to scale)

With Earth's current eccentricity, it's orbit can be visualized as an ellipse with a major axis passing through both foci and connecting the two points of greatest and least distance from the Sun (the apses) This line is also formally called the "line of apsides" and the two apses as periapsis and apoapsis from the Greek "peri" meaning around and "apo" meaning from. To be specific to the Sun-Earth system, we can substitute "helios" for the more general apsis and therefore we get the slightly more familiar terms, at least to astronomers, of perihelion and aphelion which represent the two extremes of Earth's orbit. The distance between the Earth and Sun ranges from 98% to 102% of the average distance of approximately 93 million miles, at perihelion and aphelion, respectively - a difference of roughly 4 million miles. Not enough to make you take notice, unless you design spacecraft, study solar physics, and/or like to geek out on this stuff, like me.

Earlier today, at approximately 1900 GMT (~7pm in London), we swung through that point of closest approach, marking one anomalistic year since we last passed through perihelion at midnight on January 3, 2010. Daylight may be returning, but the Sun is now receding. So continue your new year(s) celebration and wave to the Sun as it sets today, as it will rise a little farther way tomorrow.