JamesCronen.com

Welcome to the International Year of Astronomy 2009!

IYA2009 is a global effort, initiated by the International Astronomical Union and UNESCO, with participating organizations ranging from NASA, the American Astronomical Society, the European Space Agency, and likely the astronomy department of your local university.

I first heard about IYA2009 thanks to the tireless promotion of Dr. Pamela Gay of Southern Illinois University Edwardsville and AstronomyCast. I had the good fortune to speak with Dr. Gay herself last year at Dragon*Con, and she conveyed such exceptional enthusiasm for this event that I knew it had to be important.

Events for the Year of Astronomy are planned all over the world. There will be the usual conferences and meetings for the professional astronomers, but there will also be myriad museum exhibits, planetarium shows, television programs, and observation events open to the public.

Don’t we already know pretty much everything we need to know about the Earth? Why study astronomy? Space is empty. It’s dark. There’s nothing of interest except for stars and dust.

Besides, it’s exceptionally unlikely that barring enormous advances in rocketry in the next few decades any of us will leave the biosphere of Earth. Throughout our lifetimes, space travel will consist of Earth orbit, the Moon, and if we’re lucky, the neighboring planets of the Solar System (most likely Mars).

What separates humanity from the animals is our exploratory nature. Humans have always sought the next frontier, only satisfied once they have completely exhausted that which the previous frontier could give. Space is, as the voices of William Shatner and Patrick Stewart told television viewers week after week, the final frontier.

Pragmatic physicists love space because it is the only almost perfectly pure physics laboratory we know. It gives us the opportunity to examine what happens when matter interacts over huge time, distance, and energy scales. On Earth a very long-running experiment might last ten years. (The absolute longest-running experiment I can think of is approaching its eightieth birthday.)

By observing what happens in space we can watch the results of billions of years of interactions. Even better, we can literally look backwards in time. The light reaching us from the most distant quasars is at least a billion years old — that is, we’re seeing the quasars as they were a billion years ago.

By studying astronomy, we can also begin to learn about the origins of life on Earth. How did life begin? We’re taught in our science classes from a young age that the conditions needed to support life are very precarious. But how did we even get that far? Which chemical reactions occurred at just the right temperature and pressure to allow life to form? The goal of astrobiology is to answer these questions.

Finally, studying space gives us perspective. We humans are an amazingly self-centered lot. It’s worth remembering that we are such a tiny part of the universe. This famous photograph from Voyager 1, later entitled “Pale Blue Dot”, shows the Earth as just that:

That tiny pixel in the center right of the image is the Earth, as seen from 3.7 billion miles away.

I look at that image and realize that no matter how bad my day may have been, there is so much more than just me. There’s so much more than all of us. While this might make some people feel insignificant, it makes me realize exactly how special and lucky we are to live on this beautiful planet.

It is in our interest and in our nature to learn about the black skies above. Take the opportunity this year to renew or initiate your love of the cosmos.

Space.com reported yesterday that NASA astronomers have found the smallest black hole yet. The little guy has a mass of only 3.8 times the mass of the Sun and is only about 15 miles in diameter.

Gravity is the force that causes masses to be attracted to one another. On Earth, our gravity causes objects to fall towards the center of our planet at an acceleration of 9.8 m/s². That is, for every second an object falls, its downward speed increases by 9.8 meters per second. This means that if I throw something up in the air at 9.8 m/s, it will take one second before its velocity is zero again. After two seconds, the object is traveling downwards at 9.8 m/s.

There are two ways to increase the rate at which objects fall on a planet’s surface. They’re both related to the geometry of the planet.

The first approach is to increase the mass of the planet. The more mass, the greater the pull. Makes sense. The other approach is to keep the mass of the planet the same, but compress it into a smaller ball.

The “shell theorem” states that you can treat a uniformly-distributed sphere of mass as if all of the mass were located at a single point at the sphere’s center. Since we’re on the surface of the Earth, we’re exactly one Earth radius away from that single point where all the mass would be compressed:

The force of gravity experienced by both of the little scientists in this picture would be the same. However, one cannot stand on nothingness, and so this isn’t exactly a tenable situation for our little guy.

If we were to keep the mass the same but shorten the distance between us and the center of the Earth, the force would be greater since we’d be closer.

The only way to keep the mass the same but compress it all into a smaller ball is to increase the average density.

A black hole is formed when a large star dies. The star has burned through most of its fuel, and its furnace isn’t producing enough energy to maintain its own structure. Gravity causes the star to collapse in on itself until all the mass is concentrated in a very small volume.

Black holes have such an intense gravitational pull that nothing can ever escape from their clutches. Their “escape velocity”, the speed required to completely escape a planet’s or star’s gravity, is greater than the speed of light. Even though light has no mass, it is still (effectively) subjected to gravitational forces. At least that’s what Professor Einstein has had us believing since he published his theory of general relativity in 1916.

Just for fun, let’s figure out how dense this black hole is. The mass of the Sun is approximately 2.0 × 10³⁰ kilograms. That’s 2,000,000 trillion trillion kilograms for those of you that don’t like scientific notation. The mass of the black hole is 3.8 times this, or 7,600,000 trillion trillion kilograms.

Compress all of this into a sphere 15 miles across (so the radius is 7.5 miles). To find the volume of a sphere, multiply 4/3 times π times the radius cubed. This gives us a volume of 1,770 cubic miles. Or, if you like bigger numbers and smaller units, 7.3 trillion cubic meters. Then divide the mass by the volume to find the density.

This newly-discovered black hole has a density of one million trillion times that of water. For comparison, lead, the densest commonly-occurring material on Earth, has a density of about eleven times that of water.

A spoonful of this black hole would have a mass of fifteen billion tons! If my mass were compressed into a cube of this density, the sphere would be approximately six microns across. This is about one-twentieth the width of a human hair!

Physicists can usually learn a great deal from these extreme conditions. But, since light can’t escape from a black hole, no information can escape either. We have no way of observing the interior of a black hole. We only know of black holes’ existence because of their influence on the stars and nebulæ around them.

What we have learned is a new lower-limit for the size of star that will become a black hole at its death. Astronomers can now look for known dying stars of about this size and perhaps learn something about how stars die and how black holes are formed.

The asteroid belt is a collection of minor planets that orbit the Sun in the space between Mars and Jupiter. The belt is comprised of rocks of varying chemical composition from a diameter of about 950 km (the distance between New York City and Cincinnati) for asteroid 1 Ceres down to the size of tiny grains of sand. As our observing power improves, we find more and more of them.

Tens of thousands of objects in the asteroid belt have been designated — the designation is a sequential number and a name suggested by the discoverer. The names given were once based on mythology (as were the other bodies in the solar system) — 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, 5 Astræa, et cetera.

As more asteroids were discovered, it wasn’t as easy to follow the same naming convention. Places started getting added to the list: 334 Chicago, 341 California, 371 Bohemia, 416 Vaticana, 484 Pittsburghia, 2118 Flagstaff, 3512 Eriepa (yes, that’s Erie, PA).

After a while, discoverers started naming asteroids after respected people: 2001 Einstein, 2002 Euler, 2041 Lancelot, 3534 Sax (after Adolphus Sax, inventor of the saxophone), 3600 Archimedes, 13926 Berners-Lee, 18125 Brianwilson.

I did not know, however, how ridiculous some asteroid names get.

Yes, there’s 2138 Swissair (the airline).

Don’t forget 9007 James Bond, which you think would be related to 13070 Seanconnery, except for the fact that they were discovered a good eight years apart. Also note the last three digits of asteroid 9007 James Bond.

Fans of British comedy will want to observe 13681 Monty Python or 18610 Arthurdent. Sports fans will enjoy 17493 Wildcat (after the University of Arizona’s sports teams) and 8217 Dominichašek.

How about 19367 Pink Floyd? 19383 Rolling Stones? 19521 Chaos? 19535 Rowanatkinson?

My favorite: 20461 Dioretsa. The word “Asteroid” spelled backwards, because of 20461 Dioretsa’s retrograde orbit.

This is my new goal in life: Get an asteroid named after me. In the meantime, I’ll have to dream up something clever. Suggestions go in the comments below.

(Thanks, Wikipedia!)