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August 26, 2014 — A monthly look at the night skies of the northern Rocky Mountains, written by astronomers Ron Canterna, University of Wyoming; Jay Norris, Challis, Idaho Observatory; and Daryl Macomb, Boise State University.
Right after sunset, located directly overhead as part of the summer triangle, lies the constellation Lyra. Its brightest star is Vega, the fifth brightest star in the night sky. Lyra represents the lyre of Orpheus, the mythical Greek poet and musician. It is a very small constellation and difficult to outline due to its faint stars.
Sirius was the first star, other than the sun, ever to be photographed and to have its visible spectrum taken. Due to the Earth’s recession, Sirius will be the pole star around 13,750 A.D.
Lyra’s second brightest star is Gamma Lyra, or Sulafat. It is a blue-white giant star, a very close double star system that varies in brightness in about 13 days. Epsilon Lyra is called the Double Double star. Each of the two stars that one can see is an actual close binary double star.
The two most important deep sky objects are M 57, the Ring Nebula, the most photographed planetary nebula. It is a shell of ionized gas that was ejected in its past during its red giant star phase. The second object is M 56, a globular star cluster located to the southeast of gamma Lyra.
Planetary Watch: Early this month, on the southwest horizon right after sunset, you will see Saturn in Libra and Mars in Scorpio. Jupiter rises about 4 a.m., and Venus can be seen right before sunrise. It is on a journey to become the evening star.
September 2014 Interest: Interstellar Travel: Fundamentals
The vast distances between stars are the first thing astrophysicists consider when discussing space travel. The distances from our star, the sun, to our nearest stellar neighbors are several light years. The distance to the center of our Milky Way galaxy is about 27,000 light years.
The difficulties of making even the shortest interstellar trip may provide one explanation for Fermi's Paradox: Why there are roughly 500 billion stars in the galaxy but so far we have seen no clear evidence of interstellar travelers. Even before addressing the technical challenges -- development of efficient propulsion, shielding from radiation and matter impinging on a spaceship at extreme velocities, and a robust life support system -- we must consider the fundamentals for such a journey, namely the time and energy that will be expended.
The "Relativistic Rocket" site (best URL, above) gives correct formulas for calculating the relevant quantities, discussing how speeds close to the speed of light may be attained by traveling for just a few years with a mere constant acceleration of "1 G" -- the acceleration we feel toward the center of the Earth due to gravity. However, some interesting effects ensue with near speed-of-light travel.
Einstein's special relativity tells us that the times and distances experienced by the spaceship travelers compared to those experienced back on Earth will be very different. For the travelers, time slows down (time dilation) and distance traversed decreases (length contraction). These effects occur because spacetime is "hyperbolic" -- time intervals and space intervals effectively subtract from each other for travelers speeding by the nearly stationary surroundings. The benefit to the traveler is that the time expended during the journey is shortened, more so as the spaceship gets closer to the speed of light.
In a well-executed journey to the Galactic Center, accelerating at 1 G halfway and then similarly decelerating so to arrive at zero velocity, the traveler would age only about 20 years. However, back home, the Earth and everyone on it would age about 27,000 years -- the time that the relativistic spaceship traveling near the speed of light would take for the journey as observed by earthlings. The ratio of required fuel mass to space capsule mass for this journey to the Galactic Center would be roughly one billion, assuming that a 100 percent efficient propulsion system (matter/anti-matter annihilation?) could be developed.
Next time we will consider ramifications for a less arduous trip to the nearest stars, including spaceship requirements and what would be encountered along the way.
The constellation Lyra.