Early darkness allows for more star gazing
Returning our clocks to Standard Time on Saturday night has given us back the gift of early darkness in which we can explore the wilderness above. Though it looks quite still, the celestial objects glittering in our sky are changing and dynamic, with most moving at speeds incomprehensible given how still they appear.
Most of the stars of the Big Dipper, our nighttime companion through all the months of the year, are actually part of a group that was formed together about 500 million years ago. At this time, life on Earth was dominated by arthropods that primarily lived on the sea floor. Since forming in a common nebula, the stars of the Big Dipper have drifted apart (as siblings do). They continue to move as a group, moving away from our Solar System at 15 kilometers per second … that’s over 33,000 miles per hour! The X-15 that flew 6.72 times faster than sound in 1967 only achieved 4,520 mph! In spite of this great speed, at distances around 80 light years, or 480 trillion miles, we can only detect their motion spectroscopically.
Turn to the east early in the evening to find the Pleiades star cluster in Taurus. As shown on the diagram, these “Seven Sisters” will be about 40 degrees above due east at 8:30 p.m. These stars formed only about 100 million years ago, about the time that bees emerged on Earth. They are grouped much more tightly than the stars of the Big Dipper, but are also moving toward us at almost 12 km/s … 27,000 mph. Below them in the sky is the bright red star, Aldebaran (al-DEB-uh-ron, “The Follower”). It forms the left top of a V of stars that are another star cluster, the Hyades, that are coming toward us at an astounding 40 km/s … 90,000 mph!
There’s an even more amazing group of stars visible to us in the evenings of fall and winter, the great galaxy in Andromeda. This fuzzy blur can be found by the paths shown on the diagram. In on, move from Alpheratz (ALL-fur-atz) at the northeast corner of the great square of Pegasus to Mirach (MEER-rock) in the bottom curve of the cornucopia shape of the constellation of Andromeda. From Mirach, go to Mu (μ And) Andromedae on the top curve of the cornucopia, then a bit farther up and left to Nu (ν And) Andromedae. Slightly beyond and right of Nu is a fuzzy blur best seen with “averted vision.” This is a technique used to astronomers to see faint objects. The rods on the sides of our retinas are more sensitive to small variations in brightness. So look at Mu or even Alpheratz, but direct your mind to the fuzzy blur to convince yourself its really there. It might be easier to spot it with binoculars, then find it with your unaided eyes.
The other path is from Cassiopeia (an easy constellation for most to find). Above the upper (or right) side of the W, Kappa Cassiopeiae (κ Cas) is centered to create a diamond shape. Follow the line from Kappa through Schedar (SHED-der) to the galaxy.
This fuzzy blur is the largest galaxy in the Local Group, the cluster of galaxies to which the Milky Way and Triangulum galaxies belong along with more than 50 dwarf galaxies. Its light is the combined fires of about a trillion stars shining across 2.5 million light years of space. It was Edwin Hubble who first estimated the distance to the galaxy in 1925. He identified Cepheid variable stars in the galaxy by using the 100-inch telescope at the University of Chicago’s Yerkes Observatory. Cepheid variables are named for Delta Cephei (SEF-fee), shown in the small triangle at the bottom of the house shape of the stick figure used for the Constellation Cepheus (SEF-fee-us). In 1908, Henrietta Swan Leavitt, a Radcliff graduate working the Harvard College Observatory as a “computer,” discovered that the period over which stars like Delta Cephei vary in brightness is directly proportional to their luminosity, the amount of energy they emit. Comparing these measurements to the apparent brightness of the stars allows us to calculate their distances. Even today, these stars remain vitally important for measuring the distances to galaxies.
Delta Cephei itself is approaching us at about 38,000 mph. The galaxy is also moving toward us, but the galaxy is approaching at a jaw-dropping speed of almost 250,000 mph. And in about 4 billion years, it will collide with our home galaxy, the Milky Way. In this collision, it will be primarily the gaseous and dark matter halos of the galaxies that will collide, not individual stars. Figure 2 shows how the view that a resident of Earth might have in 3.75 billion years. No averted vision will be needed. If there are still intelligent beings on Earth, I hope they will enjoy the view.
Though astronomers initially assumed galaxies to be so widely dispersed in the universe that they would never collide, it turns out that galaxies tend to be gathered into clusters and galactic collisions are far from rare. Google “galaxy collisions,” click on “images,” and you’ll see dozens of them. In fact, collisions seem to be a normal part of galaxy evolution from spirals of hundreds of billions of stars to giant elliptical galaxies with tens to hundreds of trillions of stars in a process known as “galactic cannibalism.”
The astronomers of the Adirondack Public observatory will be happy to focus their telescopes on these star clusters, galaxies and other wonders from our Roll Off Roof Observatory (RORO) above Little Wolf Pond in Tupper Lake. Currently, we’re open to the public on the first and third Fridays of each month, weather permitting, of course. For updates and notices, check out adirondackpublicobservatory.org and our Facebook page. On our public observing days you can also call the RORO at 518-359-6317 to talk with one of our astronomers. Observing starts about one half hour past sunset.