Tag Archives: astronomy

The Bull of Heaven

There are so many fun visual elements in the Gilgamesh story. I think it would make a terrific graphic novel, like 300.

One lively part is when Ishtar, the Goddess of Love, wants Gilgamesh for her boyfriend. Gilgamesh says no, Ishtar gets steamed and asks the other gods to send the Bull of Heaven down to Earth to destroy him (am I the only one who thinks it really funny that the gods worry about the Bull leaving giant-sized cow-flops all over the landscape? I am? Oh). Gilgamesh and Enkidu have to fight for their lives against the Bull. For the ancient Sumerians, the Bull of Heaven was/is a constellation—a group of stars. Thousands of years later we still call that constellation ‘Taurus’—Latin for ‘Bull.’

Hey, look at Douglas De La Hoz’ interpretation of the Gilgamesh story!
Lynnie McIlvain shows us some parallels between Gilgamesh and Homer’s epics and the Bible—

I realize now I should have put horns on my Enkidu character design.

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Satellites and hamster balls

Satellites are useful for a whole bunch of purposes: talking on your cell phone; keeping an eye on the weather; broadcasting television and radio stations; seeing what your enemy is up to in times of war; communicating with people when there’s an emergency…but you probably guessed why I decided to talk about satellites.

Satellites serve the same purpose the stars did for Galileo and Maskelyne. They give you information you need to find your location on Earth. Satellites communicate with the Global Positioning System (GPS) on your phone or in the car. They constantly send out 2 bits of information: time and distance.

Most satellites orbit fairly close to the Earth, like 11,000 miles above its surface. When a satellite sends out information, its range is like a sphere—the satellite in its sphere is like a hamster in a hamster-ball.

Well, maybe not exactly, but you get the idea.

These spheres overlap. In fact, we want 3 or 4 satellite spheres to overlap. If you’re looking at your GPS device, satellites are telling it when you’re within their spheres.

So if you’re in the overlap of 2 spheres, you have a general idea where you are.

A third sphere makes that overlap even smaller, right? The smaller the overlap, the more accurately you know your position.

Then there’s a fourth sphere: Earth. You’re inside that overlap, and on the surface of the Earth.


trilateration noun

: the measurement of the lengths of the three sides of a series of touching or overlapping triangles on the earth’s surface for the determination of the relative position of points by geometrical means (as in geodesy, map making, and surveying)

triangulation noun

1 : the measurement of the elements necessary to determine the network of triangles into which any part of the earth’s surface is divided in surveying broadly : any similar trigonometric operation for finding a position or location by means of bearings from two fixed points a known distance apart

While the satellites are telling your GPS device where they are, they’re also zipping along at hundreds of miles an hour. Their positions change from second to second. All 3, 4 or 5 satellites need to tell you their positions at the exact same moment or it doesn’t work. They need a clock that’s even more accurate than Harrison’s chronometer.

https://thesciencegeek.org/2017/01/29/gps/                                                               mmmmmmmm


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Man-made moons

Okay, remember back when we talked about how Galileo thought that we could use the moons of Jupiter as a clock, and their location would help us find our location on Earth? Or how about when Nevil Maskelyne figured we could use the positions of the stars and planets to find out where we are—if we know what time it is?

Maskelyne put in a ton of night-time hours charting the courses of the stars and planets. How much easier it would have been if the heavenly bodies just told him where they are. Well, guess what? Right now, as you sit there eating your frooty kibble, there are over 19,000 moons—man-made satellites—orbiting the Earth that we shot up into space. Every last one of ‘em sends back a constant signal telling us where exactly it is, and the time.


This site shows you where every satellite is right now—https://maps.esri.com/rc/sat2/index.html
Quickie overview of satellites for kids with a charming young lady and a puppet constructed 10 minutes before showtime—https://www.youtube.com/watch?v=03pZdYVacaM

The sextant

The sextant is an instrument used to determine latitude and longitude. It was invented by Edmond Halley or John Hadley or Thomas Godfrey based on Isaac Newton’s ideas. You use a sextant to measure how far above the horizon the Sun is at noon (or how high Polaris is at night).

I’ve talked about finding your latitude or longitude by measuring the angle between a line from you to the moon and a line from you to a star. How do you do that?

Sailors have been using a sextant for centuries. Isaac Newton dreamed up the idea, then Edmond Halley built one in 1692. Several refinements were made around 1730, until we finally got the good old sextant you see people using in the movies with wooden ships and guys wearing wigs. A sextant is like an astrolabe—you sight something familiar in the sky, like a star, by lining it up along a sighter or pointer or alidade. Then you mark the alidade’s position on the frame and use that information to find your location.

Instead of an alidade the sextant has a telescope you look through. Then you find both the object (usually the Sun) and its reflection in the mirror. There are 2 mirrors facing each other and smoked lenses so you don’t fry your eyeballs. One mirror is half mirror/half glass so you can see both images at the same time. You bring the image of the Sun down to the horizon by moving the arm on the sextant and—oh, who am I kidding? Do you think I know what I’m talking about? What I need is a video to show how it’s done. Luckily, there are a bunch of them on the ol’ internet. Listen to these guys.

Here’s an in-depth 4-part tutorial covering everything you ever wanted to know about how to use a sextant.: https://www.youtube.com/watch?v=00ZEIZsl5xk

And a guy who doesn’t own a comb but knows what he’s talking about: https://www.youtube.com/watch?v=DrAkrgZRb9Y

The thing you have to know is: the sextant will give you a precise angle between 2 objects that you can transfer to a chart or map to get your position on Earth.


Look! Look! Here’s a cardboard sextant you can build yourself! https://www.landfallnavigation.com/cardboard-sextant-kit.html?gclid=CjwKCAjwq832BRA5EiwACvCWsWqv38smCfmUdVE5SqxRVkVJI_R0B9aN9jSb-3oaweER7b4KTm4iJhoCUbMQAvD_BwE

Here’s a plastic sextant—https://www.google.com/shopping/product/15301038968540324177?q=navigation+sextant&prds=epd:1143652539522712674,prmr:3,tpim:CKyp-dn168W22QEQ1N-msv7m0OotGMCbhR4iA1VTRCjg3sL8BTCNyIhA,pdprs:6&utm_medium=tu_image&utm_content=eid-lsjeuxoeqt&utm_campaign=134358029&gclid=CjwKCAjwztL2BRATEiwAvnALcqb-eUHLE4Y_XEM7QpPWFcXOcl2YbghLFCIcLIG1ItYYMc__vQ3_jBoCA14QAvD_BwE

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The clockmaker

In our last post you saw how to find your location by observing the moon and stars to calculate lunar distance. The object is to know both your local time and prime meridian time, or Greenwich Mean Time. A navigator needs to be an astronomer and a math whiz to use this method.

You may have asked yourself, “Wouldn’t it be easier to keep 2 clocks aboard the ship—one showing Greenwich Mean Time and the other kept to local time?” That’s an excellent question and I’m glad you asked it. In fact, that’s the question John Harrison asked.

John Harrison, English inventor and horologist, 1767.

John Harrison was a cabinet-maker with a side business building and repairing clocks. To win the Longitude Prize, he went for a straightforward solution: build an accurate clock that always, ALWAYS showed precisely the correct time in Greenwich.

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Lunar distancing

Okay, let’s say you’re in a rowboat at night with some friends—and you haven’t seen land for a while. You’re LOST. Nobody’s getting a signal on their cellphones, so you don’t know where you are. The strange old lady at the boat rental place left nothing but a weird navigational device; a map; and a book of star charts in the boat’s locker. Your friends are getting panicky and start blubbering. What do you do?

Because you’re a devoted reader of The Western Civ User’s Guide to Time and Space, you know exactly what to do. You tell your pals to stop their noise so you can concentrate. It’s a clear moonlit night, so you can see the moon, stars, and the horizon. You pick up the lovely brass sextant and set its sights on the moon—and a star, how about Regulus, just there to the left? You measure the altitude (how high above the horizon) of the moon; the altitude of Regulus; and the distance between them. You figure the angle of the 2 lines from you to the moon and you to Regulus. You do this measuring not in feet or miles but in degrees.

From the moon’s altitude you know what time it is (http://www.astrotulsa.com/page.aspx?pageid=27, scroll down)—and your latitude, too (http://www.lewis-clark.org/article/1268). Knowing the distance from the moon to Regulus, you pick up the book of star charts and find that lunar distance for your local time. Run your finger down the chart to find what time it is in Greenwich, England where it’s zero degrees longitude. The difference in time will tell you your longitude (15° for every hour, 1° for every 4 minutes). Find your latitude and longitude on the map and start rowing home. You don’t even need a compass—you keep Polaris, the North Star, above your right knee as you row.

You get safely back to land! Your friends can’t believe you saved the day with that stupid book. The lady at the boat rental gives you a wink and you all go home to bed.

This is how Nevil Maskelyne proposed finding your position while at sea.

I haven’t read these, but here’s a short list of books about ocean-going girls: https://books.google.com/books/about/From_Cabin_Boys_to_Captains.html?id=wBDWSAAACAAJ

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The astronomer

Gerard van der Puyl’s portrait of Nevil Maskelyne—just gorgeous. What a painter.

Nevil Maskelyne was the fifth Astronomer Royal at Greenwich Observatory. He proposed using the positions of the stars, planets and their moons as a method of calculating your position on Earth, just as Galileo had proposed using the moons of Jupiter as a universal clock. Maskelyne was a hard worker and determined to win that Longitude Prize. He believed that with accurate charts of stars’ positions, you could find longitude anywhere on Earth. At the Observatory, Maskelyne and a team of astronomers ‘worked feverishly through the year 1766, preparing tables for the new Nautical Almanac and Astronomical Ephemeris. Published first with data for the year 1767, it included daily tables of the positions of the Sun, Moon, and planets and other astronomical data, as well as tables of lunar distances giving the distance of the Moon from the Sun and nine stars suitable for lunar observations.’

Here’s Maskelyne in a nutshell:

Oops! Okay here’s Maskelyne in brief:

Sorry! Sorry! Here it is: Maskelyne’s idea was that you have a point zero of longitude—the Prime Meridian—as a reference point for time. Longitude is time measured in degrees. Each hour is 15° of longitude. When you’re at sea you take 2 measurements: the Sun’s position and the moon’s position. The Sun’s position tells you what your local time is; you find the moon’s position (the distance from the moon to one of the 9 suitable stars) in your almanac to tell what time it is at the Prime Meridian. The difference between your time and Prime Meridian time can be converted into degrees, which gives you your longitude.

You’re probably thinking: ‘Okay, Manders, how exactly do you measure the Sun and the moon? Usually when the moon’s out it’s nighttime.’ That’s an excellent point! You measure the Sun during the day and adjust the ship’s clock to the local time, maybe?






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Oh, it’s on

Offering 20,000 pounds back in 1714 was like offering millions of dollars today. Who wouldn’t want to win that longitude prize money? All you had to do was devise a precise method for finding your location on Earth.

The responses didn’t come pouring in overnight. You may have noticed that the big naval disaster on the Scilly Islands happened a whole 7 years before Parliament got around to forming the Longitude Commission. Some serious brainwork—and tinkering—needed to be put in. This was going to take awhile. As mentioned earlier, time/distance/astronomy are interlinked. The people who responded to the Longitude Commission’s offer worked in astronomy and time.

There were 2 main competitors in the race to find longitude: an astronomer and a clockmaker.

The Royal Observatory

Wren tore down the castle standing here and built the observatory out of the recycled stone. What a guy!

By now all 17 of you weirdos who’ve been reading this history have gotten the idea that time/distance/astronomy are interlinked—at least if you want to know where you are.

Eratosthanes, then Ptolemy, then just about everybody who drew a map chose their own prime meridian. That’s fine so far as it goes. But to be useful, a prime meridian needs to have an observatory. An observatory is where astronomers can keep track of the stars and regularly publish charts showing their positions and movements. Navigators can use those charts to check the stars’ positions and tell time from that information.

In ad 1675, King Charles II realized how important astronomy would be to all those ships who were expanding England’s trade around the world. He commissioned an observatory in Greenwich (a section of London) and had it designed by Sir Christopher Wren, the architect who designed pretty much every building in London.

Something I never knew before this morning: Christopher Wren was an astronomer as well as an architect. One of those professions was his side-gig. Makes one’s life achievements seem somewhat inadequate, doesn’t it? You’re welcome.


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