Upcoming Highlights
May 11, 2000 7:30P.M.- Reading Public Museum
Inge Heyer of the Space Telescope Science Institute will present a combined program on Extra- Solar Planets, and an update on the Hubble Space Telescope. The program will run approximately 90 minutes in the Planetarium.
July 13 , 2000 7:30P.M.- Reading Public Museum
Our speaker this month is our own George Babel who will talk to us about "Warm Weather Observing".George is an experienced observer, and will have many good tips for us.
August 10, 2000
No regular meeting this month. Picnic at Dave Brown's farm on Saturday August 19th starting at 5:30PM.
In this issue:
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Convention Time 2. Mythology of the night sky 3. The Hydrogen Fusion Process |
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Pegasus is a bimonthly publication of the Berks County Amateur Astronomical Society
Editor/Desktop publisher: Bob and Joanne Capone
E-Mail submissions may be made to: BobC1957@Netcarrier.com
The Mid-East Region of the Astronomical League (MERAL) will be holding a convention September 22-24 in Charlottesville, Virginia. This event is a convention and star party. The event will include speakers and workshops, vendors, door prices, a lunch and non-astronomy events around Charlottesville. I have so much information on this event that I can’t put it all in this newsletter. The Astronomy Department at the University of Virginia is making their two observators available for use! Plus there is plenty of space to set up your own scopes.
There are several hotels in that area that have reserved a block of rooms for those going to the convention. The reservation expires middle of August. If you are interested in more information, please contact me. I also have a small supply of registration forms.
MYTHOLOGY OF THE NIGHT SKY - LEPUS
We are all familiar with Orion, the mighty hunter of the night sky, along with his Hound. But did you know what Orion is actually HUNTING something in the sky? He is hunting rabbit! Located below Orion and westward from his Hound is the small constellation of Lepus, the hare. The story of how the hare was placed in the night sky near Orion comes from the Greeks of Sicily, a country noted in early days for the great devastation caused by rabbits. Sounds like they could have used a mighty hunter on earth in those days.
Other cultures, however, that did not suffer through a plague of rabbits saw something different in this star grouping. The early Arabs called the principle stars the Chair of the Giant and the Throne of the Jauzah. These stars were also called the Thirst-slaking Camels since they are located near the celestial river, the Milky Way. The earliest Egyptians called it Boat of Osiris. The Chinese called it The Shed.
Many ancient people saw a connection between The Hare and the Moon, some of them implying that the markings on the moon were made by the hare. One such story comes from the Hindu. A holy man in an early stage of his existence was a hare and, when in the company of an ape and a fox was applied to by the god Indra (hence, India) disguised as a beggar. Wishing to test their hospitality, he asked for food. All went in search for food but only the hare returned unsuccessful. To not fall short in his duty to his guest, he had a fire built and cast himself into it for the guest’s supper. In reward, Indra placed the hare in the moon.
This constellation is very low in the southern sky and looks very small. However in his star catalog, Gould finds 103 stars down to 7th magnitude! Orion and his Hound must have caught many of those stars since the time of Gould because I don’t see how there could possibly be 103 stars in this small constellation today!
Article 6, The Hydrogen Fusion Process
In the prior article we discovered that a protostar becomes a star when the nuclear fusion of Hydrogen became the energy producing process within it's core. A star in this phase of it's life cycle was called a Main Sequence star. In this article, we will describe this nuclear fusion mechanism and determine why some stars evolve much faster than others beyond the M-S stage of their evolution.
The energy production mechanism of M-S star is called nuclear fusion, specifically Hydrogen fusion. Fusion involves the fusing of atomic nuclei into new, higher mass nuclei. It is the opposite process that occurs in a nuclear reactor, where the nuclei of atoms are typically split apart by a process called fission to produce energy. In fusion, atomic nuclei are fused to form larger mass nuclei. Both fusion and fission processes are nuclear process in that they involve the nucleus of the atom. In our ordinary daily life we do not experience any processes involving nuclear or atomic reactions. All of the every day reactions or processes, e.g. rusting, digestion, are chemical reaction, involving only the electrons which circle around the atomic nucleus. Nuclear process require very high temperatures not found in the ordinary daily environment, temperatures that can typically only be generated in the cores of stars, nuclear reactors, and atomic bombs.
Only in the core of a star is the temperature hot enough, 10 million degrees, to drive a nuclear reaction. Here atoms, exist only as bare nuclei since they are stripped of all elections due to the extreme temperature. A Hydrogen atom minus it's electron is simply a proton, e.g the nucleus of the hydrogen atom. The fusion process starts when two protons (bare Hydrogen atoms) collide to form a nucleus of Deuterium (heavy Hydrogen). In the process, one of the protons converts into a neutron, emitting a neutrino and a positron particle. The created Deuterium atom then collides with another proton forming Helium3 and in the process emits a high energy photon, a gamma ray of light. Lastly, two Helium3 atoms collide forming a stable atom of Helium4 while emitting two protons. The net result of all of this activity is that basically 4 protons (Hydrogen atoms) combine to form one Helium atom, and a minute amount of mass is converted into energy which appears as a gamma ray photon. This is often referred to as Hydrogen burning although it is not a chemical burning process but rather a nuclear process. Helium4 consists of two protons and two neutrons. The net result of the conversion of two of the protons into neutrons involves the emission of a neutrino particle, a positron particle, and gamma ray photons of light. The energy we receive from the sun is derived from these high energy gamma ray photons. An interesting fact about these photons is that it takes the emitted photon about a million years to make it's way from the core of the star where it was created to the surface of the star where it is emitted. And in the case of the sun, that photon then takes only 8 minutes to reach the earth once emitted from the surface of the sun.
The efficiency of the Hydrogen fusing process increases very rapidly with increasing temperature. Since a massive star will collapse with a stronger gravitational force, it ends up with a hotter core temperature. And since the star is a delicate balance between the crush of gravity and the out-ward pressure of the generated energy, the hotter core temperature enables the Hydrogen fusion process to run faster, be more efficient, and thus generates energy faster. In a sense it's gravity-pressure thermostat is set higher than in a less massive star. Thus a massive star, although it has much more fuel than a less massive star, actually burns or fuses it's fuel at a much faster rate than a less massive star. The higher internal temperature explains the much higher observed energy output rate, evident as a high absolute magnitude for massive stars. And for massive stars, this is the reason why they exist for such a short time in the Main Sequence phase of their life cycle.
Nuclear fusion of Hydrogen into Helium is the energy producing mechanism of a Main Sequence star. The temperature of the fusion process determines the rate at which a star produces energy and thus ultimately determines how long it lives on the Main-Sequence. In the next article, we will discuss what happens when the nuclear fusion process runs out of Hydrogen and how some stars evolve into the Red Giant and Supergiant phases of stellar evolution.
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