Zodiac - intro

In a previous blog I mentioned the difference between ecliptic and equatorial coordinates. The plane of the ecliptic is important because nearly all of our solar system lies in the plane of the ecliptic.  Once interplanetary travel becomes commonplace we may abandon equatorial coordinates.  The word ecliptic is derived from the word eclipse, something that happens because the earth, moon and sun all lie in the same plane.

Today I want to teach you how to orient yourself with ecliptic coordinates.  The easiest way to do this is with the constellations of the zodiac.

The word zodiac comes from the latin word zodiacus which means circle of animals.  The signs of the zodiac do not line up with their constellations.  This is mostly due to precession.

The northern zodiac constellations are Virgo, Leo, Cancer, Gemini, Taurus, Aries and Pisces.  For me the easiest to find is Leo.  At its apex the lion lays flat on a plane elevated above the horizon in the southern sky.  The prominent sickle shape forms a mane and the bright star Regulus marks a front paw. Virgo is to the left of Leo and all the other constellations are to the right in the order above.

Zodiacal light is sunlight reflected off of interplanetary dust.  You will not see this if there is much light pollution.

If you want to spot planets I really think first you should know your zodiac.  Planets will always be in one of the zodiac constellations.

Unicode Symbols of the Zodiac

♈	Aries
♉	Taurus
♊	Gemini
♋	Cancer
♌	Leo
♍	Virgo
♎	Libra
♏	Scorpio
♐	Sagittarius
♑	Capricorn
♒	Aquarius
♓	Pisces

Some more moongazing

I figured out how to attach my telescope to a camera tripod and some other tricks.  Unfortunately the first clear night I've had in a week is a full moon.  I tried to sketch it but my confidence is naught.

When I look up at that bright celestial beachhead I am just constantly awed that what I am looking at is in fact another world.

Radiation

I've covered EM radiation in my previous post.  There is another type of radiation which has nothing to do with EM waves known as particle radiation.  Some common types of particle radiation are alpha particles, beta particles, neutrons, neutrinos and cosmic rays.

Often these particles travel very fast at significant fractions of light speed.  Unlike most type of EM radiation, particle radiation can be quite destructive, though some (neutrinos) do almost nothing at all.

Baryonic vs Non-baryonic
Particles come in all sorts of flavors.  Generally though the kinds of particles you and I might be interested in are what are called baryonic matter.  To non-particle physics baryonic matter is all the matter you will ever need to worry about.  Non-baryonic matter includes such elusive concepts as photons, the purely theoretical Higgs boson (which suposedly gives the other particles mass), practically philosophical phonons (which are what happens when sounds collapse their wave state, whatever that means).  Baryonic matter on the other hand is familiar stuff like protons, neutrons, electrons, antimatter and many more exotic particles.  Most importantly to me baryonic matter particles actually tend occasionally act like particles rather than behaving like ripples is spacetime.  Though baryonic particles may cause ripples in spacetime, they are almost never said to be ripples in spacetime.   The same can not be said for non-baryonic particles.

So particle radiation is basically like a hail of very tiny very fast BB pellets.

Electric charge
Many type particle radiation consist of particles that have positive or negative electric charge.  Alpha particles, beta particles and cosmic rays all have electric charge.

The atoms in your body, and most everyday substances, are said to be electrically neutral.  This is only true when atoms are relatively small (nearly always).  When we are talking about particles though, atoms are much much larger.

The atom is surrounded by a shell of negatively charged electroness.  The nucleus on the other hand is a densely packed cluster of positively charged protons and electrically neutral neutrons.  The whole thing is held together by forces that are beyond my (and most peoples) understanding.

The thing is though, while electrons might be electrically attracted to the nucleus something called Weak force (seriously look it up) prevents the electrons from colliding with the protons (though if that did happen charges would cancel and you would get a neutron, don't ask me how they know this).  The electrons are only weakly connected to the nucleus.  Like rebellious teenagers electrons can, and do, leave the atom if given the right influences.

Chemistry
Chemistry happens when electrons from one atom aren't content to stay with that atom but windup traveling with other atoms.

Covalent, or molecular bonds are when two atoms share electrons with each other.  This is the strongest type of bond.

Metallic bonds are when electrons are shared throughout a large crystal structure of atoms.  This is what makes metals are conductive.

Ions are atoms that are missing, or have an extra, electron and consequently carry electric charge.  Ionic bonds are when one atom takes an electron from another atom to complete an eight electron shell (this is like a greedy stamp collector stealing your stamps to complete his set).  This creates one negatively charged and one positively charged atom.  The two consequently stick to each other.  Ionic bonds dissociate in water.

Ionizing radiation
Imagine if you will, high speed charged particles reigning down on our placid molecularly bonded atoms.  If the charged particle is moving slow enough they will actually bounce harmlessly off the atoms, possibly imparting momentum but in no way altering the atom or its relationships with nearby atoms.  This is because even electrically neutral atoms have electrically charged parts.

Most of the time though the charged particle are moving very fast.  As they zip along they ionize many atoms in or near their flight path.   The high speed electric field strips atoms of their electrons.  This usually destroys whatever chemistry might have been going on.

What once was a segment of DNA that told your cells how to make that unique hue of your eyes now says nothing, it has been ripped to shreds by ionizing radiation.  You cell goes to work trying to repair the DNA, but this is like trying to reassemble documents after they have been to the shredder.  Now the instruction seem to be telling the cell to reproduce ceaselessly and ignore all pleas from your body to stop.

Months later the descendents of this cell have now formed what is known as tumor.  Before you die of cancer the doctors have a number of gambits they would like to try.  One of these is to blast your tumor with radiation.

This may sound like fighting fire with gasoline but it actually makes sense.  It was really a fluke that created the tumor in the first place.  Blasting the same cells again would cause the DNA to say something else this time, assuming the cells don't die instantly which they would.

EM radiation can also be ionizing radiation.  This hinges on frequency (wavelength) rather than total intensity.

Radioactive Decay
Certain configurations (actually most configurations out of whats possible) of protons and neutrons are intrinsically unstable.  They can emit alpha, beta and gamma radiation until they reach a stable configuration.

Nucleons are the components of an atomic nucleus.  You should probably know by now that these are protons and neutrons.

Mass number is the total number of nucleons. Uranium 235 has a mass number of 235 nucleons.

Atomic number is the number of protons.  This determines chemical properties and what element an atom is.

An isotope has a specific atomic number and mass number.  All uranium isotopes have the same atomic number but only Uranium-235 has a mass number of 235.

Decay Modes
Alpha decay is when an unstable (usually large) isotope gives up a helium size chunk of its nucleus in order to reach a more stable state.  Alpha particles are just helium atoms that have no electrons and move at excessive speeds.  Alpha decay reduces mass number by 4 and atomic number by 2.

Beta decay happens when nuclei have too many or too few neutrons.  A neutron can release energy and form a proton and an electron. A proton can turn into a neutron by absorbing energy and releasing a positron.  A positron is like an electron only with positive charge (actually its the anti-electron).  Electrons and positrons are known collectively as beta particles.  Beta particles are ejected from the nucleus at high speeds by the weak force.  Beta decay will reduce or increase atomic number by 1 while conserving mass number.  Beta particles have very little mass.

Gamma decay is just when the nucleus needs to release excess energy.  Gamma rays are released but the nucleus does not need to change mass or atomic number to do this.  Often gamma decay follows immediately after other decay modes that may have left the nucleus in an excited state.

A decay chain is the chain of radioactive unstable isotopes a nucleus will transition through until it reaches a non-radioactive stable isotope.

Half life is the amount of time it takes for statistically half of an isotope to decay into something else.  Although some isotopes have half lives of millions of years, most decay in no time at all.  The isotopes that stick around longer are more stable and less radioactive.

Gamma radiation is the most penetrating.  It can go right through your skin and even your hazmat suit with no trouble.  The best precaution is a nice thick layer of lead.

Beta and alpha radiation are less penetrating and simple rubber hazmat suit is ample protection.  The danger with alpha and beta sources is contamination.

Nuclear Contamination
So you hear that the nuclear power plant is spilling nuclear radiation into the ground water.  It must be having affect on peoples minds because they seem to think that the noun form of the verb radiate can somehow be a substance.

Can I spread intimidation on bread or sprinkle consternation on my flowerbed?  No I can not.

Radioactive substances can leak.  This is known as contamination.  Nuclear contamination is scary because if it isn't handled properly a lot of people are going to get sick, the kind of sick you don't get better from.

Blowups happen.  Your nuclear plant might only be designed to handle acts of god of certain magnitude.  Something bigger could come along and screw things up.  Though every safeguard may prevent it, sabotage or even simple negligence can conceivably cause contamination as well.

Though for every eventuality there is an SOP (standard operating procedure).  There is reason for this.  While it becomes increasingly expensive to protect a power plant from increasingly unlikely catastrophes it cost relatively little to run simulations and write documentation of steps to control the extent of damage is in those scenarios.

If you are unfortunate enough to be near a contamination there are steps that you can take that could conceivable prevent you from ever developing ill health effects.

Stay away from milk and dairy.  Meat and fish are also dangerous.  The goods already in your pantry before the spill as well as food from other non-contaminated areas should be totally safe.

Iodine pills keep iodine out.  Your body doesn't "need" iodine to fight radiation.  Rather iodine tablets clog your system with non radioactive iodine.  This prevents radioactive iodine from being absorbed latter thereby averting thyroid cancer.

Listen to the authorities.  They have a lot more training with this sort of thing than you.

When asked, evacuate.  Evacuation is a good thing.  It means that you are not already contaminated.  If you get cancer later on in life its because you kept smoking cigarettes, you dumbass.  Remember, as with any type of contamination the alternative to evacuation is quarantine.

Usually the worry with contamination is a chronic doses of radiation as the radiation lingers in a contaminated person for an extended period of time.


Neutron Radiation
Neutrons are not produced in nuclear decay and they carry no electric charge.  The pass right through electron shells like they are not even there.  They eventually slam into the nucleus and do numerous things to it.  Adding a neutron increases mass number by 1.  It also adds energy.  The old isotopes may have been stable but the new one probably isn't.  This causes it to transmute into new elements entirely.

Although neutron radiation does not ionize you can see why it is dangerous to people.  It can make non radioactive materials radioactive without physically contaminating it.  It can weaken strong materials by altering the elemental makeup.

Free moving neutrons are only created in nuclear fission and fusion reactions.  Neutrons are actually a vital part of sustaining power generating nuclear reactions.

Neutron activation analysis is a really high tech way to measure exactly what and how much elements and isotopes something has.  Scientist who need to radio date something like a fossil typically use x-ray spectrometry.  Though x-ray spectrometers are relatively cheap and even portable there is a limit to their accuracy.

I had the privilege once of working as an intern at a research reactor.  This reactor doesn't produce power.  It only produces neutrons.  It does so on demand for the sole purpose of neutron activation analysis.  This reactor is incredibly safe.  Nuclear meltdown is impossible.

Neutrino Radiation
Neutrinos like neutrons have no electrons and are also produced in nuclear reactions.  Unlike neutrons and virtually every other type of radiation no amount of shielding in the world can stop the onslaught of neutrinos.  Sounds dangerous right? Well no, not really.

Neutrinos interact very weakly with matter.  So weakly in fact that neutrinos from the sun will often pass right through the planet earth entirely without so much as an atomic jostle.  They have proven very difficult to detect.

Cosmic Rays
These are fragments of supernova or even weirder processes.  Cosmic Rays are composed of heavy nuclei that are traveling close to the speed of light.  They are quite hazardous to your health.  They are bombarding the planet all the time.  Metal shielding actually makes the problem worse because as the cosmic rays are slowed down by the atoms in the metal they release energy in the form of intense x-rays. This is called the bremsstrahlung or braking radiation.

Why are we surviving this onslaught?  We aren't.  The earth's magnetosphere actually deflects this stuff.  Astronauts are not so immune.  They have reported fireworks in their vision, even when they close their eyes.  This is the result of cosmic rays striking their optic nerve.  If just that bundle of wires detects cosmic rays about once a second imagine what cosmic rays must be doing to the rest of the astronauts' bodies.

Radiation and You
So you decided to live under a dome and swear off electrical devices. Are you avoiding radiation yet? No because there is no food you could eat on earth that isn't radioactive.  You decide to freeze yourself to be woken up at some date in the future when food becomes 100% radiation free.  How about then?  Make sure they wake you up before too long or naturally existing radioactive isotopes in your body will do more damaged than can be repaired (you can't suspend the animation of nuclear chemistry).

The atomic weight of carbon 12 (thats the normal kind with 6 protons and 6 neutrons) is exactly 12.  The rest of the atomic weights on the periodic table are based around that.  So why is it that when I look at my periodic table I see an atomic weight of 12.011 listed for carbon?

The periodic table gives atomic weight of relative abundance of the elements in all their isotopes.  The average atomic weight of any clump of carbon I pick up on earth is going to be 12.011.

Some quick back of the envelope math

1 - 12/12.011 = 0.0009

So 0.09% of all carbon on earth is something other than carbon 12 and probably radioactive.  This applies especially to living beings such as ourselves.

Organisms digest and respirate so they are constantly recycling carbon.  As long as an organism lives they maintain the same ratio of radioactive isotopes.  When an organism dies those isotopes decay without the interference of chemistry or biology.  Because the rates of decay are well known radio dating is used to determine how long something has been dead.

Light - an Introduction - EM spectrum

What do you think when you hear the term radiation. Poisoned milk? Heavy metals that stick around for millions of years? Jumping under your desk and covering your head? Brain cancer causing cell phones?

When I think of radiation I think of light bulbs, old style radiators (notice any similarity between the words radiator and radiate?) or burning ants with a magnifying glass.

Radiation comes in many flavors, one broad category of which I would like to discuss today; electromagnetic radiation aka light.

Light is a wave. Some scientist will tell you that it is a particle. These scientist aren't wrong but thinking of light as a particle can get you in trouble if you don't have some grasp of the quantum mechanics. For the purposes of this discussion (and many to come) we will treat light as wave. This is at least as valid as treating it like a particle. The material below may help persuade you.

Light is called electromagnetic radiation or EM radiation for short. To understand light it helps to understand a little about electricity and magnetism.

Electricity and Magnetism
Two like charges repel one another and two opposite charges attract. Each charge is said to have its own electric field around it that affects the behavior of other charges in that field. This field drops off with an inverse square law. Inverse square laws are common in the field of radio transmission (incidently another type of radiation).

If you were standing next to fire and decided to move twice as far away from it as you have been standing how bright would the fire seem? If you answered half as bright, you are mistaken. If you said one quarter the initial brightness, then good for you, have a treat. The same goes with broadcast radio transmissions or star brightness or electric fields. Just about anything that disperses over three dimensional space will have to weaken as it moves away from the source. It will follow the inverse square law.

This electric field follows field lines that point radially toward or away from the charge (depending on convention and weather the charge is negative or positive). In physics convention field lines are continuous and magnitude is shown by the density of field lines. Calculus is somewhat different. The density, or strength, of field lines drops of with the square of the distance.

Magnetic fields are generally the result of current. Many models of magnetism are just hypothetical loops of current. To find the conventional magnetic field direction of current imagine wrapping you right hand around the current with your thumb pointed in the direction of conventional current. The Direction you fingers curls is the direction of the magnetic field. Magnetic fields lines are said to always be continuous. They are always perpendicular to electric field lines.

EM Waves
Imagine again our charged particle.  So far I may have given the impression that field lines are infinite (if ever weakening) , but thats not entirely true.  It takes time for a filed to "set up".  Other charged particles wont "know" that another particle appeared (or disappeared for that matter) until the field lines reach them.  This follows very well known speed limit of 300,000 km/s.  For some reason this is called the speed of light but I think it might be more accurately named speed of field propagation.  This same limit applies to magnetic fields, gravity fields and everything else in the universe.

Imagine for a moment that our particle is attached to some armature that can move it up and down very quickly.  Imagine what is happening to field around the particle.  The field cannot update instantaneously so the field near the particle moves in sync with the particle but further away it does not.

Now imagine the field as a kind of elastic fabric.  Moving the particle generates circular ripples to propagate from it through the field "material".

Because it is a moving particle we can treat it as current and we can therefore predict magnetic fields as well as electric  ones.  The magnetic field is always perpendicular to the electric field.  It will propagate in a ripple pattern at the exact same speed as the electric field.

Electro magnetic waves are nothing more than this, though they may vary in the way they are generated it generally boils down to oscillating electric charges.

Radio Waves
Radio waves are a type of EM radiation that is often the result man made devices.  Current is a collection of moving charged particles.  Alternating current is a type of current that switches direction many times a second.  It is alternating current which transmits radio waves.

Because radio waves are ripples in electric and magnetic fields they can exert force on charged particles, even generate current. Wires that have their electrons moved by radio waves receive radio transmissions.  This process is called electromagnetic induction.

The Electromagnetic Spectrum
EM waves - light can exist on virtually any frequency.  At the low end in the bassists section we have radio waves which I already mentioned.  But as we move up the orchestra of the universe there are -in order of increasing pitch- microwaves, infrared, visible light (red to blue), ultraviolet, x-rays and gamma rays.

Higher frequency light tends to be higher in energy than lower frequency light.  Higher frequency also means a shorter wavelength.

Microwaves
Microwaves are just high frequency radio waves.  The reason they are dangerous to humans and make a convenient way to heat your lunch is because of that peculiar Micky Mouse of molecules, the water molecule.

Water molecules are electric dipoles. I have not the foggiest notion why this is (actually its the Mickey Mouse shape that causes it but why that shape is a mystery)  The hydrogen "ears" of the molecule are slightly positively charged and the oxygen "chin" is slightly negatively charged.  This allows life to exist and snow flakes.

Because H2O is an electric dipole it is susceptible to forces being exerted on it through EM induction, particularly in the frequency of microwaves.  When your microwave oven cooks a bowl of noodles it is using EM to shake just the water molecules.  The moving water molecules then impart heat to everything else around them.

As an experiment try heating up water and oil simultaneously in separate glass dishes.  Leave the water in for a few minutes and it will boil.  The dish with the oil in it shouldn't be heated at all.

Infrared
There are three types of ways that warm objects transmit thermal energy to rest of the universe.  They are called convection, conduction and radiation.  For this blog in general we are mostly concerned with that last one.

Everything that has a temperature radiates thermal energy.  For everyday things like people, animals and machines all of this happens in the range of infrared.  Infrared goggles are what allow the special forces to spot tangos (bad guys) in the dead of night without the add of illumination.  It is also what allows some predators to hunt at night.  There is no trick that can hide this radiation except maybe an infinite heat sink or actually lowering your temperature to background levels.

Spaceships do not have the advantage of air circulation or underground water tables to keep cool.  The only way a spaceship can release thermal energy is by radiation.  If the ships radiators fail then the crew is in big trouble.

Visible light
Visible light is just a small sliver of the EM spectrum.  It also contains the range that most of our suns energy is released at.  Our eyes evolved to take advantage of this particular bath of radiation.  I speculate that creatures that evolved around a red dwarf would see our star Sol as bluish and creatures that are born around large blue stars might see our sun as rather red.

Visible light is a higher frequency and therefore more energetic than all the types of radiation I have discussed so far.  Less energetic forms of light have less ability to penetrate and damage tissue.

It makes less sense to talk about the cancer causing potential of cellphones (radio waves) than the cancer causing potential of light bulbs.  I would say if you want to prevent cancer, live in a cave but there are reasons why that wouldn't even help anyways.

Blue light has a slightly higher frequency, and shorter wavelength, than red light.

Ultraviolet
Ultraviolet or UV light is what causes you to tan or it can cause skin cancer.  It is what makes all your white threads light up when you visit the club or it allows the dentist to more clearly see how well you've been brushing your teeth.

UV rays cause certain substances to excite their outer most electrons.  When the electrons fall to a lower energy state they release energy in the form of visible light.  Its usually safe, but from here on out radiation becomes more dangerous.

X-rays
X-rays are usually created when high speed charged particles pass through a conductor.  The charged particle slows down but all the while imparting unusually high amounts a energy to the surrounding metal.  The metal immediately releases this energy in the form of x-rays.

When you go to the doctor to get an x-ray, the technician gives you a led bib and some reassuring words then steps behind a thick lead wall.

X-rays are a little dangerous.  They are high in energy and short in wavelength.  This allows them to penetrate solid objects.  This in turn allows pictures to be taken of your beautiful insides.  Other types  of radiation bounce harmlessly off your skin but not x-rays.

For the most part you don't have to worry to much about x-rays.  There is a difference between acute and chronic doses of radiation.  The x-rays you get at the doctor are nowhere close to giving you an acute dose of radiation and because you only get x-rayed a few number of times in your whole life you are not likely to receive a chronic dose either.

For the technician it is a different story.  If they stood next to every patient who got an x-ray while they got the x-ray they would receive a chronic dose of radiation.  They would be at a high risk of cancer.

Gamma Rays
The deadliest of all, gamma rays are only produced in nuclear reactions or radioactive decay.  Gamma rays are usually associated with alpha and beta radiation (alpha beta gamma get it?).  Although alpha and beta radiation are produced in the same type of processes they are not EM radiation at all but particle radiation.

The atomic nucleus has different energy states just like the "orbital" electron shell.  Gamma rays are the result of higher energy states collapsing inside the nucleus.  Because electric forces are non negligible in their role inside the nucleus this collapse sends ripples into the EM fields around it.

Film review - Pioneer One

Pioneer One is a political thriller drama that challenges our notions of space exploration during the cold war. The show revolves around the crash of a manned Russian module, a module that modern post-soviet Russian has no knowledge of ever existing. To say much more would be to give away spoilers. The best thing about this show, its absolutely 100% free.

The show makes its money entirely through donations. It is distributed via file-sharing technology. I think the show is seen to be a proof of concept that this strategy is a viable alternative to more traditional copy-protected marketing schemes.

Anyways check it out at www.pioneerone.tv go ahead, I'll wait.

You can download add-free torrent files of the episodes (3 so far) at vodo.net as well as other totally legal to copy and distribute films.

Bicentennial of Manned Spaceflight

50 years ago to the day cosmonaut Yuri Gagarin became the first human to orbit the earth. Exactly 20 years latter NASA's space shuttle transport system was kicked off.

Last night was the first night in a few days to have a really clear view of the night sky. Unfortunately the waxing quarter moon dominated the starscape.

The first constellation I was able to recognize was Ursa Major. The term ursa major is latin for "great bear". Many distinct civilizations saw a bear, including the Greeks and Native Americans. I will tell you the Greek story of Ursa Major.

Apollo had a sister named Artemis. Artemis was more than a little crazy. She was basically a nun in that she was eternally a virgin and demanded that her pupils (young girls) also never ever have sex with anyone.

At the opposite end of the spectrum we have Zeus, a real playboy in ancient mythology. Zeus seduced one of Artemis' young companions, a young woman by the name of Callisto. Callisto became pregnant and Artemis banished her.

Callisto is not done being punished for Zeus' crimes however. Zeus' wife Hera turns Callisto into a bear after Callisto gives birth to Arcas. One day while Arcas is out hunting he nearly shoots his mother in bear form. Zeus intervened at the last moment by placing them both in the Heavens. Callisto is Ursa Major and her son Arcas is Ursa Minor.

Ursa Major is one of the largest objects in the northern hemisphere. It is also one of the most important to newcomers of astronomy such as myself as it makes a great sign post. The edge of the "cup" of the "Big Dipper" as some like to call Ursa Major points straight to the tail of Ursa Minor. The tail of Ursa Minor is the most important star of celestial navigation in the northern hemisphere. It is Polaris the "North Star".

Sketch - Small Telescope

This is a Jason 335 Comet Chaser Newtonian reflector. The diameter is 76mm. The focal length is 600mm. That is f/7.9. It has an azimuth mount. It comes with 20mm and 6mm lenses. In the picture there is a sort of extender tube thing that comes with scope. So far I have found this to be a very respectable hobby scope. The biggest drawback I have found is that the built in tripod is tiny and it has no tripod mount.

Astronomy Units - Angles and Time

I may reference this blog in the future alot.

How does one find ones way in the night sky? In ancient times constellations were the landmarks in the sky. The agrarian revolution led to the invention of more precise systems of angular measurement. Astrologers could predict the motion of the stars and planets. The invention of calendars made it possible to predict the seasons. To ancient people the math seemed like spell casting and divination and the astrologers rudimentary meteorological skills seemed like downright prophecy.

Throughout this blog I will mostly use decimal degrees or degrees minutes seconds (°, ', "). I will sometimes use time units as a sort of angular measurement (described below). When I post computer programing code, for reasons that are beyond the scope of this post, I will often use radians.

Most celestial coordinate systems are a variation of spherical coordinates. If you are lucky enough to have taken calculus you know that spherical coordinates are described with a distance and two angles. Though many star catalogs give all three values as well as other data, were are mostly concerned with the two angles. In vector terminology we are interested in direction but not magnitude.

I will refer to an object. This can be anything, such as a star, planet, spacecraft or Santa's sleigh.

Topocentric Coordinates

The first system of coordinates is the topocentric coordinates. You may also here this system called horizon or altazimuth coordinates. This system is centered around the observer. The z-axis corresponds to straight from the ground. The zenith is the highest point in the sky. The angular separation between the object and the virtual horizon (where the horizon would be if the landscape were totally flat) is called the objects altitude. The heading of the object given in degrees clockwise from true north is called its azimuth.

The advantage of this system is that it allows quick observations without needing to refer to other constellations just to know where to look. It is popular among amateur astronomers. The disadvantage is that in this coordinate system everything is moving all the time except you guide star (Polaris for the north hemisphere) and they are totally specific to your particular geographic location (your terrestrial coordinates, latitude and longitude).

Equatorial Coordinates

The angel the object makes with the equator is know as declination. Declination is positive for angles above the equatorial plane and negative for angles below. Polaris has a declination of 90°.

Right ascension is usually measured in hours, minutes, and seconds east of the first point of Aries. The first point of Aries is where the sun crosses the equator each year during the vernal equinox.

Azimuth telescope mounts are good for finding objects with topocentric coordinates. Equatorial mounts are good for finding objects with equatorial coordinates and tracking objects as they arc across the sky. For high magnification telescopes or astrophotography you will want an equatorial mount with a clock drive. A clock drive will move the telescope at exactly the rate of rotation of the earth along the axis parallel to the earth's rotation.

Precession and the Ecliptic

Equatorial coordinates seem fine and dandy until one day, say two thousand years from now, you realize that Polaris simply doesn't point due north anymore. The process is known as precession. The earth always maintains an axial tilt of 23.4° but it tends to wobble like a top. Geographic north moves through a complete circle every 26,000 years. The equinox or solstice occurs at different times of year throughout the precession. Star catalogs, which publish data in equatorial coordinates, are only accurate for the published epoch.

In ancient times the vernal equinox happened in the constellation Aries. The summer solstice happened in Cancer. The winter solstice happened in Capricorn. Now thanks to precession names like the Point of Aries, tropic of Cancer and tropic of Capricorn just don't make any sense anymore.

The solution is to use a coordinate system that will be rock steady for the next four and a half billion years. I am talking about the plane of the ecliptic. The plane of the ecliptic is the plane that the earths orbit around the sun inscribes. Coordinates are given in ecliptic latitude and ecliptic longitude. Unfortunately the individuals who devised this system chose to place the zero point at the vernal equinox so this coordinate system is still subject to the affects of precession.

The ecliptic is useful in observing planetary bodies as most inscribe paths across the sky that are very close to the ecliptic.

Abreviation	Name
a	Altitude
A	Azimuth
dec or δ	Declination
R.A. or α	Right Ascension
H	Hour Angle
β	Ecliptic Latitude
λ	Ecliptic Longitude

Time

Time as is used everyday is known as solar time. A 24 hour day is the amount of time it takes the earth to rotate about 361° degrees. The extra degree is the angular quantity the earth revolved around the sun in one day.

Astronomers sometimes prefer a quantity called sidereal time. One sidereal day is the time it takes the earth to rotate exactly 360°. One sidereal second is exactly 15 seconds of arc.

Moon Gazing; First Night Out

Tonight was the first night I started moongazing.  I decided not to try any sketches tonight, but instead just allowed myself become familiar with the equipment.

I have this Jason 335 Comet Chaser.  It has a focal length 600mm, diameter of 76mm and a Dobsonian mount; nothing to write home about. I used a 20mm lens and a lunar filter.  I also tried a Barlow lens but I believe that it only magnified the image without adding definition.

This telescope belongs to my father but he has not used it in years so I thought I would put some good use to it.  I have found virtually no information about this telescope on the web.   I would like to learn about lens care or any other useful information.  I know Jason is part of Bushnell but there is no mention of Jason anywhere on the Bushnell site, lease I can find.  If anyone knows anything about this yellow orange Japanese made hobby telescope, please let me know.

The Dobsonian has this tiny little tripod.  I did not have a good table to put it on, so at first I was on the ground.  The moon was setting into the northwest where there is a tall line of trees from my driveway.  I had to move the telescope numerous times just to keep my view from being obstructed.  In frustration I eventually decided to take the scope down to the local park.

Finally things were interesting.  I found a picnic table with a clear(ish) view of the northwest horizon.  Even though I was only meters away from some bright sodium street lights I discovered with pleasure that they did not interfere with my ability to see the moon.

In spite of all this I had trouble viewing detail.  I was able to make out The Sea of Crisis and the Sea of Fertility. I could see some craters as well but my lunagraphy is not adept enough yet to identify them, even with a field guide.  Part of my trouble is the telescope and partly haze.

Despite difficulties I think this was a good first night and I look forward to doing it again.  Next time I will post sketches I promise.