Bakersfield Night Sky – May 16, 2015
By Nick Strobel
Yesterday, several hundred Bakersfield College students received their associate degree diplomas. According to a recent national research study, these students from Bakersfield, Delano and surrounding areas join the ranks of BC alumni who will get on average a 17% boost in annual earnings thanks to BC. Almost as fun will be next Saturday's free public star party hosted by the Kern Astronomical Society at Panorama Park from 8 to 10 PM. The Moon and planets, including Saturn, will be bright targets to see along with beautiful star clusters and nebulae. Observing will start soon after sunset and go to about 10 PM, depending on foot traffic. Saturn will be rising at sunset. The rings have opened up quite a bit, so they'll be easy to see in the KAS telescopes. The opening up of the rings is also why Saturn is appearing so bright in our sky. In fact, Saturn is the brightest it has been for eight years.
The attached star chart shows next Saturday's sky at 9 PM. The Waxing Crescent Moon (just two days from First Quarter) will be just below Jupiter between the constellations of Cancer and Leo. Saturn will be low in the southeast just above the head of Scorpius. Bright Venus will still be up in the sky. Look for the super-bright "star" about a third of the way up in the western sky between the two Gemini brothers. Again, the public star party is free, so check it out!
One solar system object we won't be viewing through the telescopes is Pluto but thanks to the New Horizons mission, we're now getting some intriguing images beamed to our computer screens as it closes in on Pluto for its fly-by on July 14th. The latest batch of images released a couple of weeks ago show a time-lapse image of Pluto and its largest moon, Charon, orbiting around their common center of mass (also called the "barycenter"). Because Charon is so large in comparison to Pluto, the center of mass is well outside the bounds of Pluto in the open space between Pluto and Charon. The next closest in (dwarf) planet-to-moon comparison is the Earth and the Moon. The Moon is just 1/81 the mass of the Earth, so the Earth-Moon barycenter is in the Earth's interior.
Though still just a few pixels across, the images of Pluto are showing what looks like polar caps. The latest batch of images are about the same resolution as what we get from the HST but soon Pluto will become much clearer. What will we see? Alan Stern, Principal Investigator for New Horizons, says we don't know. "No one does. That's what makes this distant exploration so very exciting, so suspenseful, and so wonderful!"
Competing for dwarf planet media attention is the Dawn mission's exploration of Ceres. The two bright spots seen in one of the craters continue to be mysterious. the Dawn team welcomes your vote on what they could be on their "What's the spot on World Ceres?" webpage at www.jpl.nasa.gov/dawn/world_ceres . Just click one of the icons to cast your vote. Choices include: volcano, geyser, bright rock, ice, salt deposit, and "other".
Now for a much darker subject. An early result from the Dark Energy Survey is a map of the dark matter over a small patch of sky. There is approximately five times as much dark matter as ordinary visible matter. Dark matter is "dark" because it does not interact with the electromagnetic force like ordinary matter does. We can only detect dark matter from its gravitational effect. However, gravity depends only on mass and distance and not composition nor charge, so we're having a hard time figuring out what it is.
Part of figuring out what it is will be finding out how it is distributed in our universe. How do you detect something that doesn't produce or block light? One way to map dark matter is to see how its gravity field bends or warps light coming from distant galaxies far behind it. Gravity is a warping of the spacetime around objects with mass. Light is bent as it passes through that warped spacetime, so the spacetime can act like a lens distorting the image of an object like a funhouse mirror.
With the funhouse mirror, if you know what the undistorted image is supposed to look like (i.e., that from a flat mirror), you can use the distorted image to figure out the shape of the funhouse mirror. Astronomers are doing something analogous with the light coming from distant galaxies to figure out the shape of the dark matter clumps. Unfortunately, most of the lensing is hardly noticeable and we don't know the true, undistorted shapes of the distant galaxies.
To get around those two problems, astronomers are using huge numbers to build up enough statistics on the distorted light from the galaxies. The early result from the Dark Energy Survey used two million galaxies to make its map. When the Dark Energy Survey is completed in the next three years, the number of galaxies analyzed will be about 200 million and the patch of sky of sky will be about an eighth of the sky or 36 times greater than the map released a few weeks ago. To do such a monumental task, the Dark Energy Survey uses a camera made of 62 CCDs each with 9.2 million pixels for a total of 570 megapixels. That's a big camera!
The preliminary map of the small patch of sky shows the stringlike filaments of matter and visible ordinary matter collecting where the concentration of dark matter is strongest just as predicted by supercomputer simulations of the development of large-scale structures. The large-scale structures look something like the criss-crossing spider webs in the Hobbit or Lord of the Rings movies but the cosmic web strands are hundreds of millions of light years long and dark matter is using gravity to trap the galaxies. As the survey continues, it will interesting to see if there are any differences between how the dark matter and ordinary visible matter are distributed and then how those differences enlighten us on the nature of dark matter.
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.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com