Bakersfield Night Sky – July 4, 2015
By Nick Strobel
The big day is almost here. The big day, of course, is New Horizons flyby of Pluto! (What other big day is there in July 2015?) In ten days (on July 14th), the New Horizons will fly by the Pluto-Charon binary system and their multiple satellites frantically taking pictures and gathering data from its suite of instruments as it streaks past at 8.6 miles per second.
Launched 9.5 years ago, New Horizons's mission is to map the global geology of Pluto and Charon, determine their composition and study Pluto's atmosphere before it freezes out. Since 1989 Pluto has been moving farther out from the Sun in its elliptical orbit. Pluto is now about -387 deg F (about 40 deg Celsius above absolute zero). Eventually, Pluto will be so cold that the nitrogen molecules in its atmosphere will be too sluggish to remain in gaseous state and they'll fall onto the surface of Pluto. That was one reason why the New Horizons wanted to get to Pluto as soon as possible.
Slightly over a year after it launched, New Horizons flew by Jupiter to get a gravity assist. While it flew by Jupiter, the New Horizons took a lot of measurements as a practice run for its Pluto-Charon encounter. The New Horizons team has had other practice sessions of the encounter sequence including working through various emergency scenarios to make sure the contingency plans and decision-making processes would work on this first-ever exploration of Pluto.
What will we find? We don't know. That's why we're going there! As of the end of June, the images displayed on the New Horizons website at http://pluto.jhuapl.edu showed that Pluto has a widely varied range of surface markings and Charon has an unexpected dark spot at its north pole. We're going to see A LOT more in the next several days. All of the high-priority reconnaissance will take place in the 48 hours around closest approach.
Closest approach to Pluto of just 7,767 miles will be on July 14th at 4:49:57 AM Pacific Daylight Time. We'll be able to see features as small as 200 feet across. Closest approach to Charon happens 14 minutes later at a distance of 17,931 miles. At 5:51 AM, New Horizons will point back toward the Sun and Earth to see how the sunlight and radio transmissions from Earth are affected as they pass through Pluto's atmosphere. Perhaps Charon will also have a trace of an atmosphere, so New Horizons will look back toward the Sun and Earth as Charon blocks them about 1.5 hours later at 7:18 AM.
Because the communication antenna and instruments are in fixed positions on the spacecraft's body, New Horizons will transmit data of the close encounter the day after closest approach. During the encounter, the baby grand piano-sized New Horizons will be spinning and tilting to various positions to get the various instruments and cameras pointed at Pluto and Charon. The first flyby data of Pluto should be received on July 15th at 12:25 PM Pacific time. Because New Horizons is so far away, it will take the radio waves from its transmitter 4 hours and 24 minutes to traverse the distance between Pluto and the Earth. The radio signals are very weak and dilute, so the data rate will be very low. Through July 20th, we'll receive a carefully selected tiny subset of data from the encounter---just 1% of the data.
Between September 14th to November 18th, we'll receive the rest of a compressed version of the encounter data. Between November 18th and October of 2016, we'll receive the uncompressed version of the encounter data. Therefore, it will be more than a year after July 14th until we get all of the data back from this historic encounter!
The cost of the mission including the launch vehicle and operations over the ten years from launch to getting the data back from the encounter is about $700 million, or about 25 cents per person in the U.S. per year.
In tonight's sky as you "oo and ah" over the fireworks up in the sky, also look at the close pairing of Jupiter and Venus. On June 30th, they were just 0.3 deg apart from each other, or less than a pinky at arm's length. Tonight they are about 2 deg apart from each other (or the distance between two knuckles at arm's length). Venus is the very bright one on the left and Jupiter the fainter one on the right. Venus will continue moving closer to the star Regulus at the end of the Sickle part of Leo over the following two weeks. Between July 11th to 18th, Venus and Regulus will fit very comfortably within the field of view of your binoculars. The Sickle part of Leo is the head and chest of the lion, so Regulus very likely is the heart of Leo.
Tonight the Moon is in a Waning Gibbous phase and won't rise until about 10:15 PM, so it shouldn't spoil most of the fireworks shows. On July 18th, it will be a thin Waxing Crescent about 1.5 deg from Venus---a beautiful photo opportunity!
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