On the next available clear night, take a break, walk outside and look up for a few moments then let your contemplations move you from this bright star to that brilliant planet swimming above your head. Whether standing or seated, your daily cares can, at least temporarily, recede as you gaze into the deep recesses that form the dark face of forever. Slowly, perhaps, you'll begin to notice new stars peeking over the roof or tree tops where, only minutes ago, dark sky existed. Although the ancients mistakenly assumed that the sky was in motion, we now take for granted the fact that it is we that are on the go. For example, over the course of about four minutes, the Moon will seem to pass through a distance equal to its diameter. The minute hand on a clock appears to move much faster than the parade of stars marching through the sky at night. Yet, all of this is an illusion- even now all of humankind is traveling at an unimaginable speed although none of us have any sensation of this epic journey!
For example, since the circumference of the Earth is about 25,000 miles and because it rotates once every twenty-four hours, a person standing at the equator is actually moving at about 1,000 miles per hour, which is considerably faster than the speed of sound. Since the Earth rotates from West to East, it would take a jet flying at Mach 1.6 towards the West to counteract this effect and keep the Sun stationary in the sky. For half the day we travel closer to the distant stars and for the other half, farther away. Of course, distance north or south relative to the equator has the effect of reducing your actual speed. For instance, people in Calgary, Alberta, Canada are moving at the sub-sonic speed of only 650 miles per hour.
Of course, the Earth is in orbit about the Sun- a 585 million mile journey that takes a year to navigate. During a given day, the Earth will move slightly over two hundred times its diameter. This translates to about 67.000 miles per hour or over ninety times the speed of sound!
The Sun is also in motion about the middle of our Galaxy. Located approximately two-thirds from the Milky Way's center, our Star makes one revolution about every 250 million years. This means our solar system has completed an estimated eighteen orbits during the Milky Way's 4.5 billion year history! To accomplish this feat requires a tremendous amount of speed- about 450 thousand miles per hour! This is almost seven times the speed of our planet's movement around the Sun and about 430 times the speed of the Earth's rotation at the equator!
But, the Milky Way is not stationary, either. For example, our Galaxy and the Great Galaxy in Andromeda (M31) are approaching each other at about 900 thousand miles per hour! The Milky Way and Andromeda Galaxies are both members of the Local Group of galaxies. The Local Group contains over thirty (relatively) nearby island universes of various shapes and sizes. This group is one of several (also relatively nearby) galactic gatherings that, in combination, form the Local Supercluster of galaxies. Interestingly, our Supercluster is moving toward something called the Great Attractor- a source of gravity with incredible strength equivalent to the mass of tens of thousands of island universes. There are other galactic superclusters and each are racing from each other at an increasing rate due to the expansion of the Universe!
It would be possible to summarize the effect of all of these motions if their speed could be compared with something stationary- this is similar to measuring an automobile's speed relative to a static road beneath its tires. Such a ruler exists and it's called the Cosmic Microwave Background (CMB) radiation. This is the residual noise from the Big Bang- the event that most scientists now regard as the origin of our Universe. Highly sensitive satellites have been able to detect a slight variance in their measurements of the CMB using the Doppler shift imparted by the Earth's relative movement. The enormous distance of the CMB makes it an essentially immovable stake. Therefore, we are now able to estimate that our local group of galaxies (which contains the Milky Way, our Sun, our planet and all of its inhabitants) is moving with the expanding Universe at a speed of about 1.3 million miles per hour!
Travelers on commercial jet aircraft have little sense of movement as they stretch their legs to, say, visit the restroom- yet, their seat seems where they left it upon return even though it has moved tens of miles during the time that intervened during their absence. We, too, are unaware of our planet's motion- each morning we awake in familiar surroundings unsuspecting that we are more than 31 million miles from where we arose the day before!
In one of the groups of galaxies that share our Local Supercluster, there lies a spiral galaxy that is tilted towards our line of sight so that we can only glimpse its profile. It's a favorite target for visual stargazers because its relative brightness allows views of the central bisecting dust lane through modest telescopes. Known as NGC 891, this galaxy can be spotted towards the constellation of Andromeda during the northern hemisphere's fall season.
It's wracked by furious new star production as evidenced by the jets of dust and gas that gush like geysers vertically above and below the dust engorged edge of its broad, flattened disk. Eventually, these streams slow their vertical ascent, shift to a horizontal orientation high above the galaxy's plane and, over time, rain inward to serve as material for future stellar births. This new image shows these trails of dust quite clearly. Located about 30 million light years from Earth, NGC 891 is one of the most photographed edge-on spiral galaxies in the northern skies.