How can latitude be determined from observation of the sky

Figure 2 An easy exercise Find your latitude on a globe. So, if you live in, say, Paris at 48 o North, Polaris will be 48 o above the Northern horizon. Put in another way - the North Star Polaris will be placed high on the sky when viewed from the Arctic 90 o from the Pole :.

Limpus and J. Click to obtain larger figure GIF, 35k. Some history During the Middle Ages, every Christian man with self-respect should visit Jerusalem at least once during his life. Bishop Nicolas from Iceland published a method to determine the altitude of the North Star and thereby to determine the geographical latitude in Figure 4. Click to obtain larger figure JPG, 85k.

This method works the following way: Lie down on the ground and put your right hand above the knee, as shown on the picture. When the North Star is right above your thumb, then you have arrived at the latitude of Jerusalem. There are several ways to do this, first of all by means of the astrolabium - an instrument applied by Columbus during his voyages to America:.

Furthermore, the geocentric perspective reinforced those philosophical and religious systems that taught the unique role of human beings as the central focus of the cosmos.

However, the geocentric view happens to be wrong. One of the great themes of our intellectual history is the overthrow of the geocentric perspective. Let us, therefore, take a look at the steps by which we reevaluated the place of our world in the cosmic order.

If you go on a camping trip or live far from city lights, your view of the sky on a clear night is pretty much identical to that seen by people all over the world before the invention of the telescope.

Gazing up, you get the impression that the sky is a great hollow dome with you at the center Figure 1 , and all the stars are an equal distance from you on the surface of the dome. The top of that dome, the point directly above your head, is called the zenith , and where the dome meets Earth is called the horizon. From the sea or a flat prairie, it is easy to see the horizon as a circle around you, but from most places where people live today, the horizon is at least partially hidden by mountains, trees, buildings, or smog.

Figure 1: The Sky around Us. If you lie back in an open field and observe the night sky for hours, as ancient shepherds and travelers regularly did, you will see stars rising on the eastern horizon just as the Sun and Moon do , moving across the dome of the sky in the course of the night, and setting on the western horizon.

Watching the sky turn like this night after night, you might eventually get the idea that the dome of the sky is really part of a great sphere that is turning around you, bringing different stars into view as it turns.

The early Greeks regarded the sky as just such a celestial sphere Figure 2. Some thought of it as an actual sphere of transparent crystalline material, with the stars embedded in it like tiny jewels. Figure 2: Circles on the Celestial Sphere.

Here we show the imaginary celestial sphere around Earth, on which objects are fixed, and which rotates around Earth on an axis.

In reality, it is Earth that turns around this axis, creating the illusion that the sky revolves around us. Note that Earth in this picture has been tilted so that your location is at the top and the North Pole is where the N is. The apparent motion of celestial objects in the sky around the pole is shown by the circular arrow. Today, we know that it is not the celestial sphere that turns as night and day proceed, but rather the planet on which we live.

It is because Earth turns on this axis every 24 hours that we see the Sun, Moon, and stars rise and set with clockwork regularity. Today, we know that these celestial objects are not really on a dome, but at greatly varying distances from us in space.

Nevertheless, it is sometimes still convenient to talk about the celestial dome or sphere to help us keep track of objects in the sky. There is even a special theater, called a planetarium , in which we project a simulation of the stars and planets onto a white dome. As the celestial sphere rotates, the objects on it maintain their positions with respect to one another.

A grouping of stars such as the Big Dipper has the same shape during the course of the night, although it turns with the sky. During a single night, even objects we know to have significant motions of their own, such as the nearby planets, seem fixed relative to the stars.

This is because they are not stars at all. We can use the fact that the entire celestial sphere seems to turn together to help us set up systems for keeping track of what things are visible in the sky and where they happen to be at a given time.

Figure 3: Circling the South Celestial Pole. This long-exposure photo shows trails left by stars as a result of the apparent rotation of the celestial sphere around the south celestial pole. In reality, it is Earth that rotates. Imagine a line going through Earth, connecting the North and South Poles. If we extend this imaginary line outward from Earth, the points where this line intersects the celestial sphere are called the north celestial pole and the south celestial pole. As Earth rotates about its axis, the sky appears to turn in the opposite direction around those celestial poles Figure 3.

The apparent motion of the celestial sphere depends on your latitude position north or south of the equator. If you stood at the North Pole of Earth, for example, you would see the north celestial pole overhead, at your zenith.

As you watched the stars during the course of the night, they would all circle around the celestial pole, with none rising or setting. Only that half of the sky north of the celestial equator is ever visible to an observer at the North Pole. Similarly, an observer at the South Pole would see only the southern half of the sky. As the sky turns, all stars rise and set; they move straight up from the east side of the horizon and set straight down on the west side.

During a hour period, all stars are above the horizon exactly half the time. Of course, during some of those hours, the Sun is too bright for us to see them. What would an observer in the latitudes of the United States or Europe see? For those in the continental United States and Europe, the north celestial pole is neither overhead nor on the horizon, but in between.

As Earth turns, the whole sky seems to pivot about the north celestial pole. They are always above the horizon, day and night. Bob King Post Author. Hi Walter, Thank you for the invite! I still haven't seen Omega Cen through anything larger than a 3-inch scope. How I'd love to wallow in all those stars in a hefty Dob. I live in Maryland near On Jun, I briefly observed Omega Centauri globular cluster using 10x50 binoculars, the GC was distinct outline peeking above a distance tree line I was on an overlook area observing EDT.

My stargazing log note states: "All along the Patuxent River banks, the chorus of the frogs last night was incredible. June fireflies lit up areas below me as I viewed looking SE and S down the river valley. Big sky view from this location. I did see Menkent star in Centaurus using the binoculars and also Iota Centauri. These were higher elevation and frame Centaurus constellation when searching for Omega Centauri. Hi Rod, Thank you! Happy to hear about the summer wildlife — a wonderful aspect of summertime observing.

I was out till 2 a. The fireflies here were also amazing. Based on their flash patterns we have at least four species. Mink frogs, green frogs and eastern toads are also calling right now.

The night just sings! Thanks Bob. It makes sense that Xi Lupi would look yellow through that much atmosphere. I'm going to try to see it from 38 degrees north during my astronomy club's monthly members night this Saturday and see what it looks like from here. Zeta Scorpii and the open clusters NGC and Trumpler 24 combine to form the False Comet asterism which is visible to the unaided eye from a dark location.

It looks beautiful through binoculars or a wide-field telescope. It culminates about 10 degrees above the horizon from my 38 degree north latitude, so I can see the asterism in binoculars without getting a crick in my neck.

I always spend some time here when Scorpius is culminating, if I've got an open view to the south. By the way, navigators use the altitude of a culminating star and it's declination to determine the observer's latitude on the surface of the Earth. If the star is on the same side of the equator that you're on, 90 degrees minus the star's altitude plus the object's declination equals your latitude. If the star is on the opposite side of the equator from you, then 90 degrees minus the star's altitude minus the star's declination equals your latitude.

This work's for the noon Sun and for stars that are transiting the meridian at night. The Sun's declination changes hour by hour, so you need to find that number in an almanac, but a star's declination changes only very slightly over decades.

You wouldn't want to use a star that is very low in the sky because atmospheric refraction would introduce a lot of random error. A couple of years ago I bought a sextant and I've been practicing celestial navigation, mostly noon Sun sights.

It's a lot of fun, but my typical accuracy is only within a few miles of latitude and worse than that for longitude. I meant to say Zeta Sco culminates 10 degrees above my horizon. The clusters are north of Zeta. Hello, Anthony.

No need to change equation, if you take southern latitude and declination with sign 'minus'. True, unless you happen to be in the southern hemisphere! You're right, it's not so simple. There is difference when declination is greater than latitude, and there is difference when we're south of equator. Good article!

I find low southern horizons from Mt.