Happy 86th birthday to Vera Rubin (b. July 23, 1928), a pioneering astronomer who uncovered the galaxy rotation problem. While attempting to explain the galaxy rotation problem, she encountered some of the most firm evidence up to that time of dark matter.
Landing on the moon, July 20, 1969.
Time for an experiment! Find a book and secure it shut using tape or a rubber band. Now experiment with spinning the book while tossing it into the air. You’ll notice that when the book is spun about its longest or shortest axis it rotates stably, but when spun about its intermediate-length axis it quickly wobbles out of control.
Every rigid body has three special, or principal axes about which it can rotate. For a rectangular prism — like the book in our experiment — the principal axes run parallel to the shortest, intermediate-length, and longest edges, each going through the prism’s center of mass. These axes have the highest, intermediate, and lowest moments of inertia, respectively.
When the book is tossed into the air and spun, either about its shortest or longest principal axis, it continues to rotate about that axis forever (or until it hits the floor). For these axes, this indefinite, stable rotation occurs even when the axis of rotation is slightly perturbed.
When spun about its intermediate principal axis, though, the book also continues to rotate about that axis indefinitely, but only if the axis of rotation is exactly in the same direction as the intermediate principal axis. In this case, even the slightest perturbation causes the book to wobble out of control.
The first simulation above shows a rotation about the unstable intermediate axis, where a slight perturbation causes the book to wobble out of control. The second and third simulations show rotations about the two stable axes.
Unfortunately, as far as my understanding goes, there’s no intuitive, non-mathematical explanation as to why rotations about the intermediate principal axis are unstable. If you’re interested, you can find the stability analysis here.Mathematica code posted here.
A few days ago, we found out that comet 67P/Churyumov–Gerasimenko is a contact binary. Now we have rotating view of it. This gif uses 36 images each separated by 20 minutes to show a 360° view of the comet. It takes the comet 12.4 hours to complete one rotation.
Read more about the comet on the Rosetta Blog.
Neil Whosis? What You Don’t Know About The 1969 Moon Landing
“Forty-five years ago, this week, 123 million of us watched Neil and Buzz step onto the moon. In 1969, we numbered about 200 million, so more than half of America was in the audience that day. Neil Armstrong instantly became a household name, an icon, a hero. And then — and this, I bet, you didn’t know — just as quickly, he faded away.
"Whatever Happened to Neil Whosis?" asked the Chicago Tribunein 1974.
This is a missing chapter in the space exploration story. We like to think that after Apollo 11, the first duo on the moon became legendary. We know the names Aldrin and Armstrong now (or, at least many of us do), and we imagine they’ve been honored and admired all this time, the way we honor our favorite presidents, athletes, and war heroes. But that’s not what happened.”
Read more from Robert Krulwich at NPR.
A Mosaic of the Tarantula Nebula
"The Tarantula Nebula (also known as 30 Doradus, or NGC 2070) is an H II region in the Large Magellanic Cloud (LMC). It was originally thought to be a star, but in 1751 Nicolas Louis de Lacaille recognized its nebular nature.
The Tarantula Nebula has an apparent magnitude of 8. Considering its distance of about 49 kpc (160,000 light-years), this is an extremely luminous non-stellar object. Its luminosity is so great that if it were as close to Earth as the Orion Nebula, the Tarantula Nebula would cast shadows. In fact, it is the most active starburst region known in the Local Group of galaxies. It is also one of the largest such region in the Local Group with an estimated diameter of 200 pc. The nebula resides on the leading edge of the LMC, where ram pressure stripping, and the compression of the interstellar medium likely resulting from this, is at a maximum. At its core lies the compact star cluster R136 (approximate diameter 35 light years) that produces most of the energy that makes the nebula visible. The estimated mass of the cluster is 450,000 solar masses, suggesting it will likely become a globular cluster in the future.”
Credit: Mazlin from starshadows.com/Wikipedia