For those of you that celebrate, appreciate, or just tolerate Halloween, I offer you a cosmic witch to look out for!

Catching some rays from Orion’s blue supergiant – Rigel, the witch is actually a reflection nebula (hence the bluish color) that is over 50 light-years long.   The Witch Head Nebula (IC 2118) is about 1000 light-years distant, so we have nothing to fear from this witch on Halloween!

Click the link for more information about, and a larger image of the Witch Head Nebula.

Till next time,

RC Davison

When I look at a globular cluster like Omega Centauri I always imagined that the 10 million stars in the cluster rotated majestically about a central mass in an orderly fashion.

Thanks to some new work by two astronomers from the Space Telescope Science Institute in Baltimore, Md, my peaceful, orderly vision of a globular cluster has been trashed!

Jay Anderson and Roeland van der Marel, using data from the Hubble Space Telescope, have measured the velocities of some of the stars at the heart of the cluster and their motion is far from peaceful!

In the close-up image below, we see the brilliant blue and red stars that reside in the center of this ancient globular cluster.  The area in the rectangle is magnified and displayed below showing the relative velocities of the stars contained within.

Source: Hubblesite.org

This motion was gleaned from images Hubble took in 2002 and 2006.  Its precise optics allowed the astronomers the ability to measure the relative motion of these stars over such a short period of time.

In the Hubble clip below, you will zoom into the heart of Omega Centauri and ultimately see the predicted motions for these stars over the next 10,000 years.  It is interesting to note that this random motion gives astronomers clues that may dispel the theory of a massive black hole at the center of globular clusters.  There may be a black hole present, but it would not be equivalent to the massive black holes found in the center of galaxies, like the one at the center of the Milky Way, which is about 4 million times the mass of our Sun.

Till next time,

RC Davison

My post on August 21, 2010, “Do They Know We’re Here?” contains a bit of misinformation, which I hadn’t thought of until reading the latest Planetary Report from the Planetary Society.

While we’ve been experimenting and transmitting radio signal for over a 100 years, those early transmissions were low frequency, typically 1 MHz or less.  The ionized layer of our atmosphere – the ionosphere, reflects those signals back down to the surface, so they won’t escape the planet.

If any of you have listened to AM radio (Remember that?) at night, you find that you can pick up stations from 100s to 1000s of miles away, whereas you can’t hear them during the day.  This is because at night, the sunlight is no longer showering the atmosphere with UV radiation, which knocks electrons off the oxygen and nitrogen atoms charging them – ionizing them.  The lower layer of the ionosphere rapidly dissipates when the Sun sets, leaving the higher layers to reflect the AM transmissions, allowing them to reach much further.

We don’t see this with our FM radios,  because they operate at much higher frequencies (in the 10-100 MHz range) and don’t rely on the ionosphere to  reflect them to your radio.  For your radio to receive your favorite FM station, you have to be able to receive the signal directly from the transmitting antenna, this is why they are called “line-of-sight” transmissions.  These higher frequencies were used commercially for FM radio and early television in the early 1930s, and they blasted right through the ionosphere and out into space.

So, a long winded explanation to say that we’ve really been broadcasting to the cosmos for about 75 years, as opposed to the 100 years mentioned in the earlier post.

Comments always welcome!

Till next time,

RC Davison