Bakersfield Night Sky – December 19, 2015
By Nick Strobel
This month is the century anniversary of Einstein's publication of the General Theory of Relativity, often shortened to "General Relativity". In General Relativity, Einstein extended his Special Relativity theory (published ten years before) to include gravitation, so it worked in a broader range of conditions. Special Relavity introduced the idea of spacetime since time and space once thought to be independent of each other as described by Newtonian physics, were actually intricately linked together. General Relativity says that this spacetime becomes warped around objects with mass and the curved paths we see objects take is actually the objects following the shortest distance between two points in curved spacetime. An analogy is the seemingly curved path that intercontinental flights from Los Angeles to London take over Greenland on a flat map. If you stretch a string tight on a globe between Los Angeles and London, you'll see that the string goes over Greenland.
This stretching of spacetime has been confirmed many, many times to the point where General Relativty has even played the starring role in Hollywood films (e.g., Interstellar). One recent astronomy discovery used stretched spacetime to see something that should have been too faint to see. A team of astronomers were able to detect a small galaxy from a time period of about 400 million years after the Big Bang. Small galaxies like it have been too faint to see before and are probably more representative of the first galaxies than the extraordinary ones detected in earlier observations.
The warping of spacetime around a closer galaxy cluster can make the spacetime around the galaxy cluster act like a lens or magnifying glass that redirects light back toward our direction. Without the gravitational lens, the light from a very distant object would spread out in all directions equally with just a tiny, tiny fraction reaching the Earth. With the gravitational lens, more of the light from the small galaxy nicknamed "Tayna" ("first-born" in Aymara, a language spoken in the Andes and Altiplano regions of South America) is bent towards us making the small galaxy look 20 times brighter than normal. Some 22 other young galaxies were found by the team using this technique. See www.jpl.nasa.gov/news/news.php?feature=4780 for more details.
Earlier this month was the launch of the LISA Pathfinder spacecraft that uses an advanced thruster system developed by NASA/JPL to very precisely control the position of the spacecraft to within a millionth of a millimeter (a millimeter is the finest tic mark on a typical metric ruler). Such precise positioning will be used by the full-blown LISA mission that will launch in the 2030s to detect gravitational waves---ripples in spacetime produced by accelerating bodies such as binary black holes or neutron stars, exploding stars, and other disturbances in the force.
LISA (Laser Interferometer Space Antenna) will use an array of three spacecraft, separated by one million kilometers from each other in an equilateral triangular formation, to measure the stretching and squeezing of spacetime as gravitational waves from a distant violent event pass through the array. The three spacecraft will notice that the distances between them change by less than a picometer due to the gravity ripples. The LISA Pathfinder launched in early December is a technology pathfinder---testing one key component of the future LISA mission. For more about LISA and gravitational waves see www.elisascience.org .
One last General Relativity story is the Event Horizon Telescope project to directly image a black hole. Black holes are extremely compact, so their boundary, the event horizon, is incredibly small. Even a supermassive black hole such as the 4-million solar mass one at the center of the Milky Way is too small from our distance to view it with regular telescopes. You need something that could see a poppy seed in New York City from Bakersfield.
Astronomers working on the Event Horizon Telescope (EHT) project will be able to do this with a planet-sized array of radio telescopes located in Chile, Europe, North America, Hawaii, and Antarctica. Furthermore, it will observe at the wavelength band of about 1 millimeter that passes easily through all the dust clouds that block our view of the galaxy center at the optical wavelengths our eyes can see. We should start receiving images from EHT in the next year or so.
In the much flatter spacetime sky of Earth you will see the brilliant stars of Orion rising up in the east a little over an hour after sunset. The even brighter star, Sirius, in Canis Major will become visible shortly after 8 pm low in the east and rising ever higher as the night progresses. It will be highest due south shortly before 1 AM. See the second star chart below.
For solar system objects, the pre-dawn morning is the time to observe. At 6 AM, you will be able see the planets Saturn, Venus, Mars, and Jupiter in that order from lowest to highest in the sky. The first star chart below shows this view. I also note the position of Comet Catalina. You will probably need binoculars to spy it in our Bakersfield sky.
The December solstice is at 8:48 PM Pacific Time on December 21st. That marks the beginning of our season of winter and it is when the Sun stops its southward motion among the stars. The Moon tonight will be in a Waxing Gibbous phase in the stars of Pisces. It is heading toward Full Moon on the night of December 24th/25th, so Santa should have no problem seeing where to land on the rooftops.
Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
Many blessings to you this holiday season and I hope you all have an excellent 2016!
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com