# What is Longitude: Definition and 41 Discussions

Longitude (, AU and UK also ) is a geographic coordinate that specifies the east–west position of a point on the Earth's surface, or the surface of a celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians (lines running from pole to pole) connect points with the same longitude. The prime meridian, which passes near the Royal Observatory, Greenwich, England, is defined as 0° longitude by convention. Positive longitudes are east of the prime meridian, and negative ones are west.
Because of the earth's rotation, there is a close connection between longitude and time. Local time (for example from the position of the sun) varies with longitude, a difference of 15° longitude corresponding to a one-hour difference in local time. Comparing local time to an absolute measure of time allows longitude to be determined. Depending on the era, the absolute time might be obtained from a celestial event visible from both locations, such as a lunar eclipse, or from a time signal transmitted by telegraph or wireless. The principle is straightforward, but in practice finding a reliable method of determining longitude took centuries and required the effort of some of the greatest scientific minds.
A location's north–south position along a meridian is given by its latitude, which is approximately the angle between the local vertical and the equatorial plane.
Longitude is generally given using the geometrical or astronomical vertical. This can differ slightly from the gravitational vertical because of small variations in Earth's gravitational field.

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1. ### I Converting Longitude coordinates to feet (for separation)

I have two longitude decimals readings and they are .11330 apart how many feet is this?
2. ### Comp Sci Draw Longitude Lines of a Sphere on a Circle

I'm trying to draw a 2D globe
3. ### Longitude contraction / time dilatation

I get the same values for both observers, which is not nice I think.
4. ### I Finding the Sun's Angle from Longitude, Latitude & Time/Date

If you had your longitude/latitude, and the time/date, how could I go about working out the angle between your normal and the sun? At first I was doing a simplistic approach of assuming elliptical orbit in only two dimensions and that the Earth is a perfect sphere,Can I get a more accurate...
5. ### B Zero degrees longitude on other planets

Does anyone know if there is any internationally agreed method for determining where zero degrees longitude is when mapping other planets etc.?
6. ### I Why on Earth's surface, longitudinal or merediance lines are perpendicular to equatorial line?

I think its a defination to have infinite longitudnal lines , if line are not perpendicular than the infinite point will not add up to give the circumferance of equator, please help
7. ### Galactic longitude and radial velocities

Hi, I'm pretty happy with my answer to part i). But could I get guidance for my answers to part ii), iii) and iv). I think they are correct... However I'd like to understand that with the data provided is there a way of actually determining the distance for each component to the GC and...
8. ### Shortest Distance Between Two Latitude/Longitude Coordinates

Homework Statement We need to find the shortest distance between two given cities. For this I'll use Bangkok, Thailand (13°N, 100°E) and Havana, Cuba (23°N, 82°W ). Earth is assumed to be perfectly spherical with a radius of 6.4x106m. These aren't the places we were given but the coordinates...
9. ### Euler angles in latitude longitude space

In most physics introductions Euler angles(pitch, roll, yaw) are defined with respect to Cartesian coordinate system. If I chose not to use a Cartersian coordinate system but instead use a latitude, longitude and a proprietary vertical coordinate(and no back transformations to Cartersian...
10. ### Calculating the latitude/longitude from known distance

For a small distance (in the range of 10's of metres) how can I calculate the latitude/longitude of a point if I know the distance in ΔN and ΔE from a known latitude/longitude using the 'flat earth' assumption? Thanks in advance :)
11. ### Measuring the current Longitude and Latitude of your current position

Is there such a electronic device that measures the current Longitude and Latitude of your current position on the Earth?
12. ### Calculating latitude and longitude at any time

Calculating latitude at noon is easy: say I got ##73^o## on 6/20/2014 So, ##90^o-73^o=17^o## then ##17^o+(\frac{1}{91})^o=17.01^o##(i forgot how to find N or S:biggrin: Calculating longitude is also easy: First I set my watch to 12 00 at solar noon. Then, I find the time difference between my...
13. ### Latitude & longitude & air pressure

Hi there, I have a peculiar question. Imagine that you are in a Earth position, obtained by google, that gives you the latitude and longitude. Those values are given in the decimal notation (ex: lat=20.44 ; long=-8.5). Now imagine that you want to know the air pressure in your position...
14. ### Calculating longitude and latitude given the duration of sunset

Hello! I've been trying to solve this problem for some time but I can't seem to find the answer. Can you help me? Homework Statement On the night of 5th april an observer watches the sunset(η = 3.5 minutes,η = correction of time). The solar disk touched the horizon at 20h 02 m 02 s and then...
15. ### Longitude problem on a Terrestrial Sphere

Homework Statement How far apart (in miles) are 2 points on the equator if their longitudes differ by 1 degree? The correct answer is 69.8 miles, I'm not sure if typo Homework Equations S=r\theta radius of Earth = 3959 milesThe Attempt at a Solution \theta = 1\deg*\frac{\pi}{180}...

archeoastronomist are bufled at polinesian finding out longitude without a clock here the concept i just found out how to prove: you have a dial with two geared counterotating needles you move by hand every rotation of the sun around you you rotate a needle ten times with which the...
17. ### Longitude of the Ascending nodes (calculation, wrong data perhaps?)

Question: Calculate the Longitude of the Ascending node for a satellite of Tundra Orbit. Satellite's longitude of perigee is 21.8 degrees and its argument of perigee is 270 degrees. Satellite must cover an Earth station with 21.8 degrees longitude and 63.5 degrees latitude. My approach...
18. ### How to get longitude from Two Line Element (TLE)

Dear All I want to know the formula to extract the longitude of the satellite from the TLE below. I hope someone can help. Thanks 1 24652U 96063A 97251.85429118 .00000144 00000-0 00000-0 0 568 2 24652 0.0850 104.0202 0008355 303.2059 279.6585 1.00288964 3492
19. ### Longitude conversion according to your latitude

I have two latitude/longitude points. They are really close together. What I want to do is find the difference between the two longitides and calculate how many yards that would be. If I did the calculation with with the two latitudes, it would be just 2025yds per minute of latitude. However...
20. ### Converting RA & Dec into Normal Earth Surface Latitude & Longitude

Good Day Everyone, Been searching this site and the internet for over a week and have not found the answer to my questions. What I want to do, is take the sun's and moon's RA and Dec and convert them to their normal Earth surface coodinate (latitude & longitude). Also, should I be using...
21. ### Longitude and Latitude to Distances

Hi, How can I calculate the longitudinal and lateral displacement from the longitude and latitude in degrees from a GPS. Thx!
22. ### Comp Sci Display city and time by Longitude in JAVA

Java Help! I have Duty for my Jave class, My teacher needs to disply city and time by Longitude. which I set up to GMT but I have trouble problem. code seems to me work fine, I can't figure out wht's problems. it will be nice to get from you help. package worldclockdriver; import...
23. ### Converting Longitude and Latitude into Meters

Hi, I'm trying to convert latitude and longitude into meters (x,y). I was thinking of UTM however I don't understand the equations as the ones I've seen just go on forever. Could somone help me understand how to use these equations? heres the website that I've been trying to understand...
24. ### Calculating Distance Between Copenhagen and Rome on Same Longitude

Assuming that the Earth is spherical and recalling that latitudes range from 0° at the Equator to 90° N at the North Pole, how far apart, measured on the Earth's surface, are Copenhagen (55.67° N latitude), and Rome (41.90° N latitude)? The two cities lie on approximately the same longitude. Do...
25. ### Ecliptic Longitude Measurement

I have an idea how to measure the ecliptic longitude with a sundial type device. Ecliptic longitude is a astronomical variable so I chose this forum. Suppose we have a verticle flag pole poised on the equator of the Earth. A "coordinate circle" is drawn that surrounds the flag pole, radius =...
26. ### How is Heliocentric Earth Longitude Measured?

Hello, in heliocentric coordinates the longitude of the Earth on april 15, 2010 is 204.91°... well I know that the longitude in ecliptic system (centered on the Earth ) is measured from the vernal equinox... if i started measure from V.E. in heliocentric system too I would find the Earth in...
27. ### The equations to convert x,y,z to longitude and lattitude?

Greetings, I am trying to figure out how to convert an x,y,z coordinate to longitude and latitude (or right ascension and declination). Center of Earth is origin, of course. Thanks
28. ### Lattitude and Longitude to X,Y

I was writing a program to place a markers on a map of the United States, for a Civil War battlemap generator. I tried this: Assuming x,y and lat/long are superimposed yet different coordinate systems. For example, if a coordinate system with a unary equivalent to 12 on the other were to...
29. ### Latitude 56°30'38.00'' N, Longitude 20°59'47.00'' E

I am at 56°30'38.00''N 20°59'47.00'' E
30. ### Longitude and Latitude angle at 12M

At longitude = 0 and latitude = 0 what angle does it make at midnight? And where is long=0 located, Greenwich, England?
31. ### Mesh my data with latitude and longitude

I want to put my data on a map with coastline but I don't know how to do it. my data has a value on each (lat, lon). I can draw the figure by surf command and indicate it's coordinate by using meshgrid. I want this figure contains coastline so I used hold on to keep the original figure and...
32. ### Ecliptic Longitude and Right Ascension of the Sun

Here's a question. Where do the ecliptic longitude and the right ascension ( of the Sun )reach their maximum difference? What is the declination for these events? What calendar dates do you suppose this happens? I know the answer. I've never heard anyone make this observation except me. These...
33. ### Find Longitude of Sun - Learn How Now

How do you know where the Longitude of the Sun begins?
34. ### Geometric algebra: longitude and latitude rotor ordering?

[SOLVED] geometric algebra: longitude and latitude rotor ordering? Was playing around with what is probably traditionally a spherical trig type problem using geometric algebra (locate satellite position using angle measurements from two well separated points). Origin of the problem was just me...
35. ### Latitude Longitude -&gt; Polar Form -&gt; Cartesian Coordinates

[SOLVED] Latitude Longitude -&gt; Polar Form -&gt; Cartesian Coordinates Homework Statement I need to convert 46 Degrees North 80 Degrees west into Cartesian coordinates, based on the assumption that the Earth is a sphere (althought it's not). Homework Equations...
36. ### Astronomy - Latitude and Longitude problem

Homework Statement An airliner flies from London Heathrow (latitude 51^{o}30' N, longitude 0^{o} 10' W) to Tokyo Narita (latitude 35^{o} 40' N, longitude 139^{o} 45' E). Assuming that the Earth is spherical and the aeroplane takes a great circle route, a)what is the total distance flown...
37. ### Accepted value of G with longitude

Hey I have a lab write up due, and on it I need the accepted value of g and to get it at my longitude, any idea what this means, and how I can figure it out
38. ### UMC Time, Right Ascension and Longitude

Where can I find a triplet of UTC Time, Right Ascension (of zenith) and Longitude, preferably with many, many safe decimal places?
39. ### MATLAB Reading Text File with Latitude, Longitude & Station Name

Hi, I have a text file with 3 columns (latitude, longitude, & station name) and 51 rows. Using fscanf I am able to read the first row of the file but not the whole file. Any ideas of how to read to the end of a text file that contains both numbers and letters? This is what I have...
40. ### Latitude and longitude of the most northern point

How would one find the latitude and longitude of the most northern point traveling from Vancouver to New York along the shortest path (great circle)?
41. M

### Time change and degrees longitude

The problem states: Travelers reset their watches only when the time change is 1.0 h. How far, on avg, must you travel in degrees of longitude until your watch must be reset by 1.0 h. I don't really understand what this question is asking for, but I attempted to "solve" this by keeping in...