Sextant - Blog Posts
Navigating Space by the Stars
A sextant is a tool for measuring the angular altitude of a star above the horizon and has helped guide sailors across oceans for centuries. It is now being tested aboard the International Space Station as a potential emergency navigation tool for guiding future spacecraft across the cosmos. The Sextant Navigation investigation will test the use of a hand-held sextant that utilizes star sighting in microgravity.
Read more about how we’re testing this tool in space!
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Neutron Stars Are Weird!
There, we came right out and said it. They can’t help it; it’s just what happens when you have a star that’s heavier than our sun but as small as a city. Neutron stars give us access to crazy conditions that we can’t study directly on Earth.
Here are five facts about neutron stars that show sometimes they are stranger than science fiction!
1. Neutron stars start their lives with a bang
When a star bigger and more massive than our sun runs out of fuel at the end of its life, its core collapses while the outer layers are blown off in a supernova explosion. What is left behind depends on the mass of the original star. If it’s roughly 7 to 19 times the mass of our sun, we are left with a neutron star. If it started with more than 20 times the mass of our sun, it becomes a black hole.
2. Neutron stars contain the densest material that we can directly observe
While neutron stars’ dark cousins, black holes, might get all the attention, neutron stars are actually the densest material that we can directly observe. Black holes are hidden by their event horizon, so we can’t see what’s going on inside. However, neutron stars don’t have such shielding. To get an idea of how dense they are, one sugar cube of neutron star material would weigh about 1 trillion kilograms (or 1 billion tons) on Earth—about as much as a mountain. That is what happens when you cram a star with up to twice the mass of our sun into a sphere the diameter of a city.
3. Neutron stars can spin as fast as blender blades
Some neutron stars, called pulsars, emit streams of light that we see as flashes because the beams of light sweep in and out of our vision as the star rotates. The fastest known pulsar, named PSR J1748-2446ad, spins 43,000 times every minute. That’s twice as fast as the typical household blender! Over weeks, months or longer, pulsars pulse with more accuracy than an atomic clock, which excites astronomers about the possible applications of measuring the timing of these pulses.
4. Neutron stars are the strongest known magnets
Like many objects in space, including Earth, neutron stars have a magnetic field. While all known neutron stars have magnetic fields billions and trillions of times stronger than Earth’s, a type of neutron star known as a magnetar can have a magnetic field another thousand times stronger. These intense magnetic forces can cause starquakes on the surface of a magnetar, rupturing the star’s crust and producing brilliant flashes of gamma rays so powerful that they have been known to travel thousands of light-years across our Milky Way galaxy, causing measurable changes to Earth’s upper atmosphere.
5. Neutron stars’ pulses were originally thought to be possible alien signals
Beep. Beep. Beep. The discovery of pulsars began with a mystery in 1967 when astronomers picked up very regular radio flashes but couldn’t figure out what was causing them. The early researchers toyed briefly with the idea that it could be a signal from an alien civilization, an explanation that was discarded but lingered in their nickname for the original object—LGM-1, a nod to the “little green men” (it was later renamed PSR B1919+21). Of course, now scientists understand that pulsars are spinning neutron stars sending out light across a broad range of wavelengths that we detect as very regular pulses – but the first detections threw observers for a loop.
The Neutron star Interior Composition Explorer (NICER) payload that is soon heading to the International Space Station will give astronomers more insight into neutron stars—helping us determine what is under the surface. Also, onboard NICER, the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) experiment will test the use of pulsars as navigation beacons in space.
Want to learn even more about Neutron Stars? Watch this...
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The hardest part of determining longitude was figuring out how sailors could find their longitudinal coordinates at sea. There were a lot of methods proposed but adding a ship into the equation makes precision difficult. Learn about the Longitude Act of 1714 and how, even though this podcast loves astronomy, the astronomical method might not always be the best option.
Below the cut are my sources, music credits, a timeline of the astronomers and engineers and clockmakers I mention, a vocab list, a really cool resource that lets you drag continents all over a flattened map of Earth to compare their sizes at different latitudes, and the transcript of this episode. Let me know what you think I should research next by messaging me here, tweeting at me at @HDandtheVoid, or asking me to my face if you know me in real life. And please check out the podcast on iTunes, rate it or review it if you’d like, subscribe, and maybe tell your friends about it if you think they’d like to listen!
(My thoughts on the next episode were the Voyager golden records, space race history, the transit of Venus, or maybe something about the Moon landing. I’m loving Edmond Halley again these days, too. I’m prepping to interview a friend about her graduate-level research into the history of the universe and possibly dark matter, too. Let me know by the 20th and I’ll hopefully have the next podcast up on September 25th! If not then, I’ll push for October 2nd.)
Glossary
azimuth - a section of the horizon measured between a fixed point and the vertical circle passing through the center of an object. See example in the link.
equator - Earth’s zero line of latitude. It’s the place on Earth where the Sun is directly overhead at noon on the vernal and autumnal equinoxes.
kamal - an Arabic navigation tool consisting of a knotted string and a piece of wood. A navigator would tie a knot in the string and, by holding it in their teeth, sight the North Star along the top of the wooden piece and the horizon along the bottom. To return home, the navigator would sail north or south to bring Polaris to the altitude they had observed in their home port, then turn left or right and sail down the latitude, keeping Polaris at a constant angle. Over time, Arab navigators started tying knots at regular intervals of a fingerwidth, called an issbah, that’s about 1 degree and 36 minutes.
magnetosphere - an invisible barrier that surrounds a celestial objet. It is often generated by the movement of the liquid metal core of the object. Around a planet, it deflects high-energy, charged particles called cosmic rays that can either come from the Sun or, less often, from interstellar space.
prime meridian - Earth’s zero degree of longitude. In current maps and time zones, this invisible, imaginary line runs through London, England.
sextant - a device used to determine an observer’s location based on the observation of a known celestial object and a lot of calculation. It is still in use by sailors.
tropic of cancer - a line of latitude that marks where the Sun will be at noon on the summer solstice.
tropic of capricorn - a line of latitude that marks where the Sun will be at noon on the winter solstice.
Script/Transcript
Sources
Longitude at Sea via The Galileo Project at Rice University
Vitamin C necessity via University of Maryland Medical Center
Scurvy via NHS
Scurvy via the Encyclopedia Britannica online
An interactive map that shows how our current map distorts land masses by letting you compare different countries’ sizes.
Sobel, Dava. Longitude. Walker & Co.; New York, 1995.
“anyone living below the Equator would melt into deformity from the horrible heat” (3).
“It simply urged Parliament to welcome potential solutions from any field of science or art, put forth by individuals or groups of any nationality, and to reward success handsomely” (53).
Timeline
Claudius Ptolemy, Greek (100-170 CE)
Johannes Werner (in Latin, Ioannis Vernerus), German (1468-1522)
Tycho Brahe, Danish (1541-1601)
Galileo Galilei, Italian (1564-1642)
Giovanni Cassini (in French, Jean-Dominique Cassini), Italian/French (1625-1712)
Christiaan Huygens, Dutch (1629-1695)
Sir Isaac Newton, English (1642-1726/7)
Ole Rømer, Danish (1644-1710)
John Flamsteed, English (1646-1719)
Edmond Halley, English (1656-1742)
John Hadley, English (1682-1744)
John Harrison, English (1693-1776)
Thomas Godfrey, American (1704-1749)
John Bird, English (1709-1776)
Larcum Kendall, English (1719-1790)
James Cook, English (1728-1779)
Nevil Maskelyne, English (1732-1811)
John Arnold, English (1736-1799)
Thomas Earnshaw, English (1749-1829)
Intro Music: ‘Better Times Will Come’ by No Luck Club off their album Prosperity
Outro Music: ‘Fields of Russia’ by Mutefish off their album On Draught
Observing stars is all well and good, but how can I use stars to make my life easier? With a few handy tools and a lot of complicated math and careful table scouting, of course! Okay, it’s not actually any easier to tell where you are, predict when the Sun will rise or where the star Rigel will be at 11:36pm EST, or guess when the next eclipse will be using these tools, but if you don’t have a computer handy maybe it will help.
I did my best to describe all these odd devices in the clearest terms I could but you can hit me up with questions if you have them! Definitely check out some of the video links if you can’t quite picture what I said. I’m also on Twitter at @HDandtheVoid if you’d rather ask me there. And please check out the podcast on iTunes, rate it or review it if you’d like, and subscribe! I’ll always post all the extras here on Tumblr but iTunes is probably more convenient for downloading.
Below the cut are my sources, music credits, vocab list, and the transcript. I mention a play and a story/book and quote an astronomy book in this episode so if you want to see that written down, those sources are there as well. Let me know what you think of this episode, let me know what you think I should research next*, tell me a fun space fact… anything’s helpful!
*(My thoughts were planets, spectroscopy, or Edmond Halley. Let me know by the 6th and I’ll have the next podcast up by July 17th!)
Glossary:
armillary sphere - a device showing the apparent daily motion of the Sun depending on the season, the date, and the latitude of observation. See example video in the link.
Antikythera Mechanism - a device used to establish a calendar based on the Metonic Cycle; eclipse prediction; the location of planets, the Sun, and the Moon on a particular day; and determine the phase of the Moon on a particular day. See example video in the link.
astrolabe - a device for measuring the altitudes of certain celestial objects and for calculating latitude before the development of the sextant. One side is indented, the space called the mater, and can hold a plate depicting the local latitude. Over this plate is a rete, which points out different fixed stars as well as the Sun’s ecliptic, divided into 30 degree sections representing the zodiac signs. On top of the rete was a clock-like hand that stretched the diameter of the astrolabe, called the rule. The rule and rete could be rotated over the face of the plate. See example in the link.
azimuth - a section of the horizon measured between a fixed point and the vertical circle passing through the center of an object. See example in the link.
declination - the angle of the Sun relative to the equator. The Sun’s angle changes with the seasons.
ecliptic - the path of the Sun over the course of a year.
exeligmos cycle - a cycle that is 3 times the saros cycle, or 669 months. It is more accurate means of predicting eclipses and additionally predicts eclipses that will be visible from a location close to the initial eclipse.
kamal - an Arabic navigation tool consisting of a knotted string and a piece of wood. A navigator would tie a knot in the string and, by holding it in their teeth, sight the North Star along the top of the wooden piece and the horizon along the bottom. To return home, the navigator would sail north or south to bring Polaris to the altitude they had observed in their home port, then turn left or right and sail down the latitude, keeping Polaris at a constant angle. Over time, Arab navigators started tying knots at regular intervals of a fingerwidth, called an issbah, that’s about 1 degree and 36 minutes.
metonic cycle - a 19-year cycle developed by the Babylonians to sync their lunar months with the solar year. In the Metonic cycle, there would be 12 years that lasted 12 lunar months and 7 years that lasted 13 months.
saros cycle - a cycle of 223 months that is used to predict eclipses.
sextant - a device used to determine an observer’s location based on the observation of a known celestial object and a lot of calculation. It is still in use by sailors.
stereographic projection - a process for depicting a spherical, 3-dimensional object on a flat surface. An imaginary line is drawn from one point on the object to a point on the flat surface, following an angle to achieve the same relationship between each point on the object. See example in the link
Script/Transcript
Sources:
Video of how to use an armillary sphere
History of the armillary sphere via University of Cambridge
Video lecture on using an armillary sphere. It sounds like he’s trying to sell it.
Video of how to use an astrolabe
Make your own astrolabe suggestions via In the Sky.org
An old guy kept up a website on astrolabes but he died in April 2016, it’s very sad. Excellent info though.
Explanation of unequal hours
Pullman Car Hiawatha summary, just to prove it’s a real play
Chaucer’s Canterbury Tales with its brief astrolabe mention
Video on how to use a sextant
The many uses of a sextant via Classic Sailing
Why a sextant works via Trailnotes
The history of the sextant
The definition of azimuth
The definition of declination
Video of Antikythera Mechanism’s virtual model based on a theoretical and mechanical model. Just a theoretical model!
Antikythera Mechanism via Smithsonian Magazine
The Antikythera Mechanism Research Project website
Antikythera Mechanism via The New Yorker
Saros cycle via NASA
Saros and Exeligmos cycles
Crouper, Heather and Nigel Henbest. The History of Astronomy. Firefly Books: Buffalo, NY, 2007.
“The circular gear wheels of the Antikythera Mechanism reflect the ancient Greeks’ preoccupation with circles—and with the idea that everything in the sky moves around in circular paths, because the heavens are the home of perfection, and a circle is the ideal shape.” (59)
Intro Music: ‘Better Times Will Come’ by No Luck Club off their album Prosperity
Filler Music: ‘Brooklyn Nights Guitar’ loop from Garageband
Outro Music: ‘Fields of Russia’ by Mutefish off their album On Draught