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It’s taken 400 years of scientific discoveries to make it possible for anyone to find his location anywhere on the globe using GPS. //
With the letters GPS, we instantly recognize an innovation that has revolutionized our lives. The concept was born half a century ago in a sweltering room at the Pentagon over Labor Day weekend in 1973.
That’s the genesis of the concept for a constellation of platforms orbiting the Earth, transmitting radio signals to determine location. Many years of calculation, experiment, and miniaturization led to the Navigation Signal Timing and Ranging (NAVSTAR) satellites that became known as the Global Positioning System (GPS). //
Our society has been blessed with rare and precious genius that has combined across centuries to yield the civilizational achievements we enjoy today. Orbital mechanics originated from careful geometric analysis by Johannes Kepler in the 17th century. Two centuries later, electromagnetism was empirically measured by Michael Faraday and mathematically characterized by James Clerk Maxwell.
Atomic oscillation arose from the quantized radiation law Max Planck discovered, while Albert Einstein discovered relativistic effects, both in the early 20th century. These were the giants on whose shoulders later scientists and engineers stood to build their guideposts in the heavens.
While only a tiny fraction of the electorate understands the enormity of government waste, fraud, and abuse, now and then we learn of some extraordinary achievements underwritten with your tax dollars. GPS is one of them.
Question 1: “Has anyone tried flying from Aisa to the U.S. on a straight line path?”
YES! Every day. Remember that a great circle path is the ONLY straight line between two points on the planet.
Forget about paper maps. There are several different types (projections) and they all provide a distorted view of the earth. Take a look at the globe illustrations above. The “curved” line only looks curved when you looking at it from an angle. When you look at the route from directly above, the line is straight. When flying this line in an aircraft, the nose of the jet (assuming no wind) points straight down the line, pointing at the destination. The aircraft never turns. As you pointed out, the compass and our heading move significantly as we scoot across the globe, but the aircraft remains flying the straight line. The reason for heading changes is that we are using magnetic or true north as our heading reference point. If it were possible to move magnetic north to Hong Kong and use Hong Kong as our “North” reference, we would maintain the same heading all the way Hong Kong.
You can prove this for yourself using a globe and a piece of string as I did in the article. Play with it a bit. Stretch the string in a straight line between New York and Hong Kong (or anywhere else). Looking directly above it, it should appear straight. //
Stephen Kosciesza says:
FEBRUARY 3, 2017 AT 9:54 AM
A comment, if I may, rather than a question. It’s sort of a corollary to all that you’ve said, and it looks at the picture sort of the other way round. I’ve looked at some of the questions asked; I’m not sure if this will confuse or clarify.
If you start flying exactly north or south anywhere in the world, and you keep flying straight, you’ll continue to fly north or south (at least until you get to the North or South Pole).
If you start ON THE EQUATOR, and fly exactly east or west, and you keep flying straight, you’ll continue to fly east or west.
Begin flying in any other direction–or begin flying east or west, somewhere away from the Equator–and you will have to turn gradually if you want to keep the same geographical heading (I deliberately avoid calling it the same “direction”).
So as a broad example, if you’re in the northern hemisphere and you set out flying east (or, for that matter, northeast or southeast), you have to keep bearing left in order to maintain east (or northeast or southeast).
I think a good way to picture this, in your mind or on a globe (NOT a paper map!) is to consider a trip going always east at a high latitude–i.e., one of the circles very near the North Pole. It’s easy, then, to see that from the plane’s point of view, it’s flying in a circle going left.
As another exercise, imagine that you are 50 feet from the North Pole. You face east, and start walking–always east. You’ll have to walk in a circle roughly 300 feet (more exactly, 314.15926… feet) around, constantly turning left. If you do not, you will walk east for ONE INSTANT, and then you’ll be going more and more south of east. Walk/swim the same way for long enough, and you will pass a point 50 feet from the South Pole–walking east for one instant before heading more more north.
Great Circle Map displays the shortest route between airports and calculates the distance. It draws geodesic flight paths on top of Google maps, so you can create your own route map.
Enter two or more airports to draw a route between them on the map and calculate the distance.
Enter two or more airports to draw a route between them on the map and calculate the distance.
CAPTION:
The shortest distance between two points on a globe is not always a straight line—it’s an arc called a great circle.
TYPE: Illustration
The shortest distance between two points on a globe is not always a straight line—it’s an arc called a great circle. This complicates long-distance navigation. Rather than stay on a constant heading, pilots must regularly adjust their course to stay on the arc. The great circle effect is most dramatic near the Poles.
The Prime Meridian is the universally decided zero longitude, an imaginary north/south line which bisects the world into two and begins the universal day. The line starts at the north pole, passes across the Royal Observatory in Greenwich, England, and ends at the south pole. Its existence is purely abstract, but it is a globally-unifying line that makes the measurement of time (clocks) and space (maps) consistent across our planet.
The Greenwich line was established in 1884 at the International Meridian Conference, held in Washington DC. That conference's main resolutions were: there was to be a single meridian; it was to cross at Greenwich; there was to be a universal day, and that day would start at mean midnight at the initial meridian. From that moment, the space and time on our globe have been universally coordinated.
Sir Ernest Shackleton led famed expedition that became timeless story of human survival.
In 1915, intrepid British explorer Sir Ernest Shackleton and his crew were stranded for months on the Antarctic ice after their ship, Endurance, was crushed by pack ice and sank into the freezing depths of the Weddell Sea. Today, the Falklands Maritime Heritage Trust and National Geographic announced the discovery of this famous shipwreck, nearly 107 years later, 3,008 meters down, roughly four miles (6.4 km) south of the ship's last recorded position.
The shipwreck is in pristine condition partly because of the lack of wood-eating microbes in those waters. In fact, the Endurance22 expedition's exploration director, Mensun Bound, told The New York Times that the shipwreck is the finest example he's ever seen; Endurance is "in a brilliant state of preservation." The expedition has released the first images of the wreck—the first time anyone has laid eyes on Endurance since its sinking a century ago. Bound et al. included shots of the stern (with "ENDURANCE" clearly visible), the rear deck and ship's wheel, and parts of the deck and hull. //
Shackleton's brilliant navigator, Frank Worsley, painstakingly calculated the coordinates for the position where Endurance sank using a sextant and chronometer. He recorded that position in his log book: 68°39'30" south; 52°26'30" west. But there was some question as to the accuracy of the marine chronometers he used to fix longitude, which would have affected the final coordinates. //
The wreck of the Endurance is a historical monument, marked for preservation under the terms of the Antarctic Treaty, so nothing was touched and no artifacts were removed. The images and scans that are still being collected will be used in a planned NatGeo documentary (to air this fall), as well as for educational materials and museum exhibits. You can check out NatGeo's short TikTok video announcing the discovery below.
In 1971, the United States Navy launched the Omega navigational system for submarines and surface ships. The system used radio frequencies and phase difference calculations to determine global position. A network of eight (VLF) transmitter sites spread around the globe made up the system, which required the cooperation of six other nations.
Omega’s fix accuracy was somewhere between one and two nautical miles. Her eight transmitter stations were positioned around the Earth such that any single point on the planet could receive a usable signal from at least five stations. All of the transmitters were synchronized to a Cesium clock and emitted signals on a time-shared schedule.
LOP-thumbA ship’s receiving equipment performed navigation by comparing the phase difference between detected signals. This calculation was based around “lanes” that served to divvy up the distance between stations into equal divisions. A grid of these lanes formed by eight stations’ worth of overlapping signals provides intersecting lines of position (LOP) that give the sailor his fix.
In order for the lane numbers to have meaning, the sailor has to dial in his starting lane number in port based on the maps. He would then select the pair of stations nearest him, which were designated with the letters A to H. He would consult the skywave correction tables and make small adjustments for atmospheric conditions and other variances. Finally, he would set his lane number manually and set sail.
You timed your question well - in exactly a week we will have the 20th anniversary of the Omega system permanent shutdown.
Kritchlow said: ↑
What exactly is "Omega"? ...Is the signal transmitted from the ground?
Not is but was. We are taking past tense here. Yes, a number of countries participated to have this almost global aviation/oceanic global navigation system through system of ground antennas/transmitters. The best positional accuracy you could achieve was about 3-4 miles. VLF don't 'bounce', they hug the terrain, can go around mountain ranges, all that by the principle of diffraction. My atomic watch today is also getting 'synced' up using (similar) LF signal (antenna in Fort Collins, Co). Omega receiver was a small suitcase -like box and I bet you needed a trained operator. I think (I could be wrong) Omega was ultimately much more popular on water than in the air.
This is a quick writeup of a lesson on how GPS (or in general, satellite based navigation) works. I’d like to thank Jasper Vos and Michel Dingen of OBS De Notenkraker for the opportunity & the very useful feedback on the lessons!
Context
10-11 year old children mostly have phones here, and almost all of them turn out to have location sharing turned on with their parents. They also use their phones while on holiday to figure out where they are.
A smattering of kids here knew that phones use satellites for precise positioning, and one or two even know about GPS. So that is good!
It also turns out there is healthy interest in discovering how it actually works.
With the advent of mandated computerized surveillance, Big Brother is indeed watching. Here’s what you can, and can’t, do about it.
Mark 3 Marine SextantSometimes referred to as a "lifeboat" sextant, the Mark 3 is an inexpensive training sextant. Yet this model has taken sailors around the world, too! It is full-sized and has sunshades, but no optical magnification to help you find dim celestial with instruction booklet.
Description
Mark 3 Marine SextantSometimes referred to as a "lifeboat" sextant, the Mark 3 is an inexpensive training sextant. Yet this model has taken sailors around the world, too! It is full-sized and has sunshades, but no optical magnification to help you find dim celestial with instruction booklet.
Features & details
The Mark 3 is a plastic Training Sextant
Comes with Instruction Booklet
The Mark 3 Sextant has taken Sailors around the World
Sometimes referred to as a "Lifeboat" Sextant
It is Full-Sized and has Sunshades, but no optical magnification to help you find dim celestial bodies
Product Description
With just four required items: 1-This all inclusive book (with simple terms, teaches you how to use a sextant/navigate and includes all celestial data needed till the year 2056), 2-sextant, 3-compass and 4-universal time (shortwave radio or time piece) you can navigate the globe by using latitude and longitude derived from the sun with these four items and have peace of mind knowing that you have a reliable backup to GPS. Once you have your position in latitude and longitude, this book teaches you basic navigation (destination, heading and distance), so you will never be lost.For safety reasons and because equipment fails, batteries die, and equipment falls overboard, people going to sea should have at least two different methods of navigation. The preferred primary method is using a GPS system. This book will teach a secondary backup method of my version of the “Noon Shot Fix”.If you are headed offshore, just curious about celestial navigation or have an old sextant and wonder how it works, buy this book with the other required items and you won’t be disappointed. This book can be read in a short amount of time with sextant readings starting immediately. This book is a combination of basic theory, teaching only what you need for a noon shot fix and basic navigation/plotting, along with a checklist type form to calculate your position, all inclusive celestial data, many “completed” examples and information on emergency navigation.There are many other great celestial navigation techniques out there that people use every day, however many of these techniques require more dedication to learn/use. My goal was to create a simple book, that could be used by the average person with no background on the subject, and contain all the information needed that could be called on in a time of emergency. Anyone with basic math skills can learn/use this technique.
About the Author
Greg was a Second Class Petty Officer in the US Navy, a Sergeant in the US Marine Corps Reserve and has a Master’s Degree in Electrical Engineering. //
Douglas Smith5.0 out of 5 stars
Reviewed in the United States on March 6, 2017
An easy path to basic celestial navigation
In today’s world, it is incredibly easy for a casual, or even an experienced sailor to become totally dependent on GPS for the safe navigation of his vessel. For any sailor who ventures beyond sight of land and club house flag of his home marina, it is dangerous to be lulled into this dependency!
GPS receivers, and even the GPS satellite system are not perfect. Receivers fail, batteries go dead, and satellites suffer outages. Every sailor should possess the navigation and piloting skills necessary to bring his vessel safely home in an emergency.
The most basic “backup” navigation and piloting technique, using a sextant to compute Lat/Long and a magnetic compass to reckon direction, requires no power, electronics or radio navigation signals.
Unfortunately, teaching oneself celestial navigation is an overwhelming task for the average boater! A naval, or merchant marine officer dedicates an entire one semester course to this topic.
Greg Boyle’s book is not a comprehensive guide to celestial navigation. It will never find a home in an Annapolis classroom! But it will teach a complete neophyte a few basic celestial navigation and piloting techniques sufficient to bring him safely home in an emergency.
The celestial navigation portion of the book is dedicated almost exclusively to one specific celestial observation – observation of the sun at “Local Apparent Noon” (LAN).
This one technique is an excellent choice for emergency navigation:
• The LAN sun is one of the easiest observations to make with a sextant
• This single sextant observation yields BOTH Latitude and Longitude
• The “reduction” of the LAN observation to a Lat/Long fix is relatively easy
Greg’s book provides a step by step guide to the LAN shot. Everything from calibrating and observing with a sextant, to a simplified method of computing the “fix”. Numerous examples are included.
Any reader with a calculator and an understanding of very simple algebra will soon be successfully “shooting the sun”.
The book also teaches the reader basic piloting techniques which require only a magnetic compass.
I recommend this book to a newcomer who wishes to learn emergency navigation, and especially to sailors who have “tried and failed” to learn celestial navigation using other books.
Most average sailors will successfully complete this course. They will experience that special (and usually surprising) satisfaction the first time they shoot the sun, and using only a sextant and an accurate watch, compute a Lat/Long position which MIRACULOUSLY agrees with their GPS!
Fidsplice
5.0 out of 5 starsVerified Purchase
Reviewed in the United States on May 31, 2013
An extremely good product - great value. When you see it you'll realise you would be nuts not to buy it.
This is an exceptional and elegant description of "why", "what you are doing" and "how to get a result" in celestial navigation. So much teaching in this subject is procedural without explanation. This brief card cuts through to the guts of the problem.
I will recommend it without qualification to whoever wants to listen, regardless of the fact that someone scewed up in the production layout so that you can't break off the stub as they suggest. (You'll see what I mean when you buy it, but my recommendation is "Buy it!!")
Davis started out making the mark 15 in the 1960S and it remains popular today. Made of stabilized impact-resistant plastic, Davis sextants have circled the globe for decades. Includes carrying case and Instruction booklet
3 x 27mm Star telescope and 7 sun shades
Traditional half-silver split image mirror
Made of stabilized high-impact and weather-resistant plastic ///
REVIEW
San Franciscan4.0 out of 5 stars
Reviewed in the United States on February 6, 2017
Know why you want one and when to use it before buying
After spending a long time reading reviews for Mark 15, Mark 25 and Mark 3, Astra IIIb and other sextants, also after finishing my celestial navigation course and playing with a couple of very different types of sextants and taking sightings, I went ahead and bought a second hand but practically unused Mark 15 and decided to write this review. I will explain my reasoning below but if you are in the process of shopping for a sextant, you need to think WHY you want to have one. You may think it is obvious and the same for everyone, but it is not. I think there are at least three different categories:
1) A sextant looks so cool, I want one.
2) I am an off-shore sailor. Having GPS is good but what if it stops working because of lightning, cyber war, apocalypse etc.
3) I am into stars, I like gadgets and I am a geek of sorts. I want to learn more and have fun (or) I want to challenge myself to navigate in open ocean by only looking at the stars, I want to be a Polynesian! (Ok, maybe by cheating a bit with a sextant, Polynesians certainly didn’t have any. But you get the idea.)
Depending on where you land on this scale, your preferences could be vastly different. I personally land somewhere between 2 and 3, I call it 2.5.
If you are in the first category and want a sextant for decoration, simply stop reading here and go elsewhere. Davis Mark 15 is not for you. While it looks like a real sextant, it is plastic and unnecessarily expensive in relative terms for a decoration purpose. There are a ton of brass sextants for prices less than $50 here and elsewhere. They look good, much better than Mark 15. They will address your need better for much less. But if you decide to buy one of those $50 brass sextants, please do all of us a favor and don’t give poor reviews because they don’t work. They are not meant to work.
Let’s now look into 2nd category. But before we go much further, let’s also do a contemporariness test. It is worth to ask if a sextant is even relevant and needed for sailing these days, with multiple different services and emerging ones like GPS, GLONASS, Galileo and Beidou and abundance of cheap receivers. It is fairly easy to carry multiple (sometimes in the order of 10 including mobile phones and tablets) receivers onboard and keep them at different places, including in faraday cages (oven) for lightning protection. That said, sailors are opinionated people and they will have very different but equally strong opinions. Have a look at what they have to say. Check this poll on Cruisers Forum, a leading web forum that brings long distance sailors and cruisers together: http://www.cruisersforum.com/forums/f121/poll-blue-water-is-a-sextant-necessary-91929.html If you have time, read 15 pages of comments as well (did I say sailors are opinionated?). At best you will see many of those contemporary sailors saying it is desirable but not required. You need to make your own conclusion and decide where you land here for yourself. If you decide you are better off by carrying more GPS receivers, then you can also stop reading and start looking for backup GPS and faraday cages.
You continue reading, so you do want to have a sextant, good. Now it may be good to give some reference point for pricing. Working brass sextants sell around $2,000, aluminum ones around $600. When it comes to plastic ones, Mark 15 is around $150, Mark 25 is around $200 and Mark 3 is around $50, which is as basic as it gets. You need to decide between these three options. As you can see, it is a very wide range. It is important to mention that these are all brand new. Sextants last LONG if used properly, especially considering that they are not used that regularly. I used a sextant from 1944 and it worked like a charm. So there is a huge second hand market. Prices vary significantly but you can find a good aluminum sextant like Astra IIIb for anywhere between $250 to $300.
The question for a used sextant is not how old it is, how well it has been taken care of and whether it actually works. But there lies the problem. If you are reading this review, it probably means you are trying to learn about sextants and do not know enough already. If that is the case, how will you know if a second hand sextant is in decent shape? This doesn’t mean that there is foul play on the side of sellers, there usually is not. I have seen many sellers saying “I don’t know if this works because I am not knowledgable on sextants, I got this from my <fill in the blanks>”. And if they don’t know if it is working and you don’t know yourself, well that is a vicious circle. So be careful when you read a review here or elsewhere when someone says “Go and buy a second hand <XYZ> sextant instead of this new one as they are the same price”. While it may be a perfectly sound advice in theory for the person giving it, it may not work that well for you in practice. Also when people say they are the same price, they usually are not. I notice about 2x price difference between new plastic sextants and working second hand metal sextants.
It is also good to ask WHEN you will use the sextant. One thing important to know about sextants is they are almost useless for proper navigation unless you have other accompanying stuff. At a minimum you need to have an almanac, which changes yearly (although there are ones that go until 2050). For finding your longitude, you also need an accurate clock (you can find your latitude without a chronometer). An error of just one minute of time means 15 miles, so the clock needs to be accurate. And on top of everything you need quite a bit of practice, it is not the most intuitive thing when you do it for the first time. Obviously there are apps and computer programs that automate the calculations but again, you assume the electronics might have fried in the very first place otherwise one of the backup GPSes would work. Also it is important to think about the context here. If you were hit by a lightning in the middle of the ocean that was severe enough to fry all electronics onboard, even if you were lucky not to have a structural damage on your boat because of that lightning, I would assume you wouldn’t be continuing your regular cruise. Instead, you will head to closest port for repairs or simply go for a landfall anywhere you can. So you will need some emergency navigation skills and tools. A sextant will be handy then, even if you may not have an up-to-date almanac. If what you are concerned about is this scenario, I would highly recommend the book “Emergency Navigation: Improvised and No-Instrument Methods for the Prudent Mariner” from David Burch. For such use, I think Davis Mark 15 or even Mark 3 are good and useful to keep onboard (more on Mark 15 vs 25 below). Would having a more expensive metal sextant be better? Presumably but I personally don’t think the difference will be materialistic enough given all other suboptimal conditions. Remember, this assumes you are in an emergency and trying to do a landfall somewhere, many more things will be suboptimal and a plastic sextant as opposed to a metal sextant may be least of your worries.
And finally if you are in the 3rd category, into serious celestial navigation for fun and you are learning and plan to use your sextant frequently, then I’d look for higher end metal sextants. Astra IIIb seems to be the decent choice when you look for reasonably priced metal sextants. Used ones sell around $300 on eBay and around $600 new.
One last note on plastic sextants. If you buy a plastic sextant (or maybe before buying one), I recommend reading “How to Use Plastic Sextants: With Applications to Metal Sextants and a Review of Sextant Piloting” again by David Burch. Plastic sextants have their quirks. Many techniques in the book can also also be recommended for metal sextants but they are more important for plastic sextants. And Burch has a note on Davis Mark 15 vs Mark 25: "[...] the full mirror on Mark 25 makes the easier sights easier and the hard sights harder.". Read the book for more details on his reasoning.
To sum up, as I said I am in category 2.5 and didn’t want to spend several hundred dollars on a metal sextant. I just wasn’t sure if I would use it frequently enough. Yet I wanted to have a sextant, to get a feel of sailing by the stars like older navigators did, and to have a gateway of last resort if everything else fails, however unlikely it may be. I eliminated Mark 25 because of above comment from David Burch and eliminated Mark 3 when I actually played with one in real life. I bought a practically unused Mark 15 for half the price, and spent the delta on the books mentioned above. If you get a sextant of any sort, I highly recommend downloading and using the open source and free OpenCPN navigation application and celestial navigation plugin for it.
Without modern electronics, how could you determine your longitude, latitude, and altitude while lost deep underground?
Altitude (or depth) can be measured with a barometer.
Latitude is doable, but tricky. Two methods come to mind, but they require staying on one spot for rather a long time to make accurate measurements.
The first option is to use a Foucault pendulum. The rate of precession of such a pendulum is directly related to latitude; the pendulum conveniently serves as its own timekeeping device, so you don't even need a pocket watch to go with it. A projector and a single-sheet conversion table would be sufficient. You just have to hang around in one spot long enough to get an accurate measure of the precession rate, which would take several hours at least, and while it could be packed down quite compactly for transport, the device would be rather tricky to set up.
The second option is to use a gyroscope. //
Longitude is much harder. //
With a combination of pocket watch and really good gyrocompass, however, you can do better. To make this work, you will need an extremely accurate gyrocompass set rotating at a known position (say, when you enter the dungeon system) exactly perpendicular to the planetary axis. If you were to stay in one place, it would appear to rotate at a known rate as the planet spins, making one full rotation every day, so you can compare its actual rotation with that predicted by your pocket watch. If you stay in one spot, they will match exactly--but if you move east or west, they won't. The difference in the actual position of your gyrocompass at any point from that predicted by the pocket watch will indicate transport around the planet's axis farther or lesser than would be accomplished by the planet's own rotation--and thus, indicates how far you have traveled across the planet yourself.
A history lesson that needs to be learned and understood.
How did this accident even happen? Some articles in the press characterized the subs as having been involved in a cat-and-mouse game that had gone too far. Indeed, such games were common between the attack submarines of rival nations, and had resulted in collisions in the past.
However, that account remains unlikely because a submarine can only play a cat-and-mouse game if it is able to detect the other ship. And in the shallow waters off of Kildin Island, it is unlikely either vessel could.
It’s tempting to think of sonar as a sort of radar that works underwater. However, water is a far less compliant medium than air even for the most modern sensors, and wind conditions, temperature variations and sounds rebounding off the ocean floor can all dramatically degrade its performance. When attempting to detect the extremely quiet submarines currently in use, just a few adverse factors can turn a very difficult task into an impossible one.
Therefore, a submarine spying close to an adversary’s home port might not be able to spot another submarine heading towards it until after the collision—which can be worse than embarrassing for everyone involved.
On February 11, 1992, the USS Baton Rouge, a nuclear-powered Los Angeles–class attack submarine, was lurking twenty meters deep in the shallow waters off of Kildin Island, fourteen miles away from the Russian port of Murmansk.
The OMEGA radionavigation system, developed by the United States Navy for military aviation users, was approved for full implementation in 1968 and promised a true worldwide oceanic coverage capability and the ability to achieve a four mile accuracy when fixing a position. Initially, the system was to be used for navigating nuclear bombers across the North Pole to Russia. Later, it was found useful for submarines.
When the eight station chain became operational, day to day operations were managed by the United States Coast Guard in partnership with Argentina, Norway, Liberia, France, Japan and Australia. Coast Guard personnel operated two U.S. stations - one in LaMoure, North Dakota and the other in Haiku, Hawaii. OMEGA employed hyperbolic radionavigation techniques and the chain operated in the VLF portion of the spectrum between 10 to 14 kHz. Near its end, it evolved into a system used primarily by the civil community. By receiving signals from three stations, am Omega receiver could locate a position to within 4 nm using the principle of phase comparison of signals. In the Royal Canadian Navy, the OMEGA system was used in the AOR, 280 and Halifax class ships.
This web page is intended to review hyperbolic radionavigation systems of the past. The systems featured here are specific to my area of interest.