Bakersfield Night Sky – April 21, 2012
By Nick Strobel
The turnout for Astronomy Day was good but the weather did not cooperate so activities outside and star-gazing did not happen. Instead of doing the Walk of the Solar System, I manned the station that had people make their own spectroscope with just a cut-out pattern on card-stock paper, glue, and a piece of a CD. The idea for the homemade spectroscope is from a fellow at the Univ Wisconsin in Milwaukee. I'm always amazed at the ingenuity of creative people and that project of making a spectroscope from everyday materials makes my list. You can check out the pattern from the link on the Kern Astronomical Society's website.
A spectroscope spreads the light out from an object (light bulb, star, etc.) into its individual colors. With hot thin gas (like the mercury vapor in a fluorescent light bulb), you will see a pattern of bright lines like a bar code and like a bar code, the particular pattern depends on the composition of the gas. While a careful analysis of the bar code will also tell you things like an object's temperature, pressure, density, speed and direction of motion, the homemade spectroscope we made is only good enough to tell the difference between one type of gas and another type of gas. More details about the use of spectra is available on my Astronomy Notes site, and selecting the "Electromagnetic Radiation (Light)" chapter link.
This being Global Astronomy Month with different astronomy events for everyone all over the globe, the Kern Astronomical Society (KAS) will be starting up their monthly public star parties. This year they will be held at Russo's Books in The MarketPlace on the fourth Saturday of the month from dusk to about 10 PM depending on pedestrian traffic. More information including directions are posted on the KAS website. This month the fourth Saturday falls on the Global Star Party night, Saturday, April 28th, where astronomy clubs around the globe will be holding public star parties. After I talk about tonight's sky, I'll give you a list of things to look for on the 28th.
We are now in the midst of the Lyrids meteor shower that happens each year from about April 16th to 26th with peak on the night of the 21st/22nd (tonight!). The Moon is a very thin waxing crescent, just one day after new phase, so it will set just after sunset and not spoil the view. Meteor showers happen when Earth goes through the dust trail left behind a comet on its elliptical orbit around the Sun. When a comet passes close to the Sun it spews out gas and dust and the dust trails along in the comet's orbit. The meteor showers appear to be coming from a particular direction in the sky so the meteor showers are named after the constellation they appear to be coming from. The Lyrids are from Comet C/1861 G1 Thatcher and appear to shoot out of Lyra which will rise at about 10:30 PM. The comet dust particles hit the atmosphere at about 30 to 40 kilometers/second and quickly burn up many tens of miles above the surface. The Lyrids will hit the atmosphere a bit faster at 49 kilometers/second. Usually, more meteors are seen after midnight because your local part of the Earth is facing the direction of its orbital motion around the Sun. Meteoroids moving at any speed can hit the atmosphere. Before midnight your local part of the Earth is facing away from the direction of orbital motion, so only the fastest moving meteoroids can catch up to the Earth and hit the atmosphere. The same sort of effect explains why an automobile's front windshield will get plastered with insects while the rear windshield stays clean. (See the "Solar System Fluff" chapter of Astronomy Notes for diagrams.) Even at its peak, though, the usually weak Lyrids will have only 10-20 meteors per hour.
The first star chart below shows the evening sky looking west-southwest at 8:30 PM tonight. Venus is now almost at the horns of Taurus. Jupiter sets just a little after 8:30 now and the gorgeous star cluster, The Pleiades at the shoulder of Taurus is now mid-way between Venus and Jupiter. The winter constellations of Taurus and Orion are getting ready to set by then. Canis Major (big dog) with brilliant Sirius at its nose or neck depending on how you connect the dots is also low in the southwest and will set by 11 PM. High up in our spring sky almost overhead is Leo with orange-red Mars near the chest of the lion. With Leo so high up in the evening, it tells us we're in the middle of spring (something people of long ago would have used to measure the passage of time). Looking east at 8:30 PM, you will find Saturn straight down from Mars about a quarter of the way up in the sky—see the >second star chart below. Saturn is continuing to move retrograde (backward) with respect to the stars and Mars has finished its retrograde motion. The bright star just to the right of Saturn is Spica in Virgo. They might just barely fit within the same field of view of your binoculars. Five times the Saturn-Spica distance to the left of Saturn is the second-brightest star as seen from Bakersfield, Arcturus, at the foot of Bootes. You can also find Arcturus by extending the curve or arc of the handle of the Big Dipper.
By next Saturday at the KAS public star party, Venus will be at the tip of the right horn of Taurus and Jupiter will have already set by 8:30 PM—see the third star chart below. Mars and Leo will be almost at the zenith directly overhead. The Moon will be at first quarter phase in the dim zodiac constellation Cancer high in the southwest. At quarter phase, the vertical relief of the craters and mountains is especially noticeable, so be sure to check out the Moon through the KAS telescopes. Just above the Moon will be the Beehive Cluster (Messier 44), another nice sight through the telescopes. Saturn will be a little higher up in the southeast at 8:30 PM than it is tonight, so it should be easily visible through the KAS telescopes. The rings are opened up about 13 degrees from edge-on, so they should put on a nice show through the telescopes.
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