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Hacker News HighlightsMar 20, 2025 | Days lengthening, AI LLM blindspots, GitHub Actions painThis is a recap of the top 10 posts on Hacker News on Mar 20, 2025.How fast the days are getting longer (2023)https://joe-antognini.github.io/astronomy/daylighthttps://news.ycombinator.com/item?id=43413935AI Blindspots – Blindspots in LLMs I've noticed while AI codinghttps://ezyang.github.io/ai-blindspots/https://news.ycombinator.com/item?id=43414393The Pain That Is GitHub Actionshttps://www.feldera.com/blog/the-pain-that-is-github-actionshttps://news.ycombinator.com/item?id=43419701Muons used to test the condition of a road bridge in Estoniahttps://news.err.ee...2025-03-2012 min
The Song of UraniaClock Around the RockWe turn to the astronomy of Mesoamerica, with a particular focus on the Maya and Aztec. The central feature of their astronomy was a pair of interlocking calendars which regulated all aspects of life. The surviving Maya manuscripts also deal extensively with the motion of Venus, which may also have driven decisions to go to war. We also look at the famous Aztec Sun Stone, the 2012 phenomenon, and the fall of the Itzá Kingdom. NOTE: The Song of Urania will be going on hiatus and will return on the first full moon of 2026.2024-11-021h 50The Song of UraniaThe Stars from StarboardThe most important application of astronomy in Polynesian societies was oceanic navigation. Polynesian navigators regularly traversed from one small island to another across hundreds of miles of open sea. To accomplish these feats of seafaring, they relied on an intimate knowledge of the night sky.2024-09-281h 02The Song of UraniaLooking Up Down UnderAboriginal Australian societies are believed to be among the oldest continuous cultures on the planet. Some of their oral traditions appear to preserve a cultural memory of celestial events from multiple millennia in the past. Aboriginal Australians were also keen observers of the heavens and recognized phenomena both common and rare, from the solstices, to solar eclipses, to auroral sounds, and stellar variability.2024-08-241h 04The Song of UraniaAd Maiorem Dei Gloriam Per AstraIn his second attempt, Matteo Ricci was able to gain access to the Forbidden City. Over the next century, the Jesuits came to surprising influence in China through their knowledge of European astronomy, though this journey was not without its perils.2024-07-201h 01The Song of UraniaWhen the Saint Comes Marching InAfter the fall of the Mongol Yuan Dynasty, the Ming Dynasty drove the few small Nestorian Christian communities in China underground and largely closed China off to foreigners. Only in the 16th century with the arrival of Portuguese traders did contacts with the West begin to be revived. The newly founded Jesuit order organized a mission to China led by Matteo Ricci. After finding his efforts at establishing a presence in the country stymied by the government, Ricci discovered that the key to securing a permanent Jesuit presence in China was his knowledge of Western astronomy.2024-06-2649 minThe Song of UraniaA Tale of Two ReformsAfter Wang Mang had usurped the Imperial throne, a disastrous series of reforms led to the collapse of his dynasty. The reestablishment of the Han Dynasty called for yet another calendar reform. About a millennium later, a group of officials, including the astronomer Shen Kuo, instigated a treacherous period in court politics by pressing for a radical set of reforms called the New Policies.2024-05-3056 minThe Song of UraniaLiu Xin's Theory of EverythingAfter Wang Mang deposed the Han Dynasty and instituted his new Xin Dynasty, he needed to promulgate a new calendar to mark the occasion. One of his court astronomers, Liu Xin, developed a new calendar that integrated the lunar and solar cycles with the planetary cycles and imbued it with numerological significance. We then talk about how Huan Tan, another astronomer of the era, would have gone about measuring the lunar mansions.2024-04-2647 minThe Song of UraniaEmperor Wu's WooWe learn about the political events and omens that led to the calendar reform of 104 BC.2024-03-2955 minThe Song of UraniaThe Guest StarsWe turn to the ways that the Chinese Emperor's astronomers predicted and interpreted eclipses, as well as the so-called "guest stars" that they occasionally reported observing in the skies. Then we discuss the role of the planets, particularly Jupiter. Towards the end we hear a few examples of astronomy in Chinese folklore.2024-03-0150 minThe Song of UraniaThe Organization of Heaven & EarthThis month we turn to the astronomy of China in the early Imperial Era. We look at the way that the Emperor's astronomers were organized within the imperial bureaucracy and then walk through the three significant cosmological theories of the era.2024-01-2943 minThe Song of UraniaThe Mandate of HeavenWe start to explore the relationship between the heavens and the Earth in Ancient China, along with the role of astronomers. One of the most important concepts in Chinese political thought to emerge from this was the Mandate of Heaven. Finally, we look at the oldest record of Chinese astronomy, the story of the astronomers Xi and Ho.2024-01-0153 minThe Song of UraniaAryabhata & the SiddhantasIn our final episode on ancient Indian astronomy, we tour the five astronomical Siddhantas, and then meet some of the astronomers whose names and works survive to us, most importantly, the great Aryabhata.2023-12-0148 minThe Song of UraniaThe Vedanga Jyotisha & BeyondWe delve into the contents of the Vedanga Jyotisha, the earliest Indian text to deal explicitly with astronomy. Then we turn to early Hindu cosmology and their explanations for various celestial phenomena, from the phases of the Moon to solar eclipses. Lastly, we briefly cover the unique cosmology of the Jains.2023-11-0331 minThe Song of UraniaWhat Happened in HarappaIndia developed one of the most advanced astronomies of any of the ancient cultures, even rivaling European astronomy in its accuracy by the 18th century. We look at how the geography of India influenced its history and then turn briefly to the little we know about the astronomy of the Harappan Civilization. Finally we end with the astronomy of the Rigveda.2023-09-3037 minThe Song of UraniaHow the Moon Became BlueWe take a break from the main narrative in honor of this month's blue moon and turn to a somewhat more frivolous topic — how the term "blue moon" came to mean the second full moon in a calendar month.2023-09-0134 minThe Song of UraniaAll Along the Watchers of the HourThis month we tour the astronomers of ancient Egypt from the Old Kingdom to the last native Pharaoh of Egypt just prior to Alexander's conquest. We look at how astronomers fulfilled their primary responsibility of keeping track of time during the night so that the priests could perform the appropriate rituals in the temple. Finally, we end our journey through Egypt with their calendar, arguably the most reasonable calendar any civilization has ever used.2023-08-0657 minThe Song of UraniaWe Need to Talk About KhufuBefore getting back into Egyptian astronomy proper, we start by looking at Nabta Playa, a site of megalithic activity in the Nubian desert during the late neolithic. Then we turn to the megaliths the Egyptians are best known for — the pyramids. The pyramids have remarkably precise alignments to the cardinal directions and the techniques the Egyptians used to set these alignments remains a mystery. Finally, we look at the largest of the pyramids, Khufu's pyramid, whose so-called ventilation shafts have a possible astronomical connection.2023-07-0534 minThe Song of UraniaEgypt in a Nut-ShellWe turn to ancient Egypt, one of the oldest and most beguiling of the ancient civilizations. Egypt is particularly notable for the sheer conservatism of its civilization and changed little in more than two millennia. After a brief overview of its geography, history, and textual sources, we look at Egyptian conceptions of the creation, structure, and end of the universe.2023-06-0648 minThe Song of UraniaThe Astronomy of Saharan and Sub-Saharan AfricaThe oldest plausible astronomical artifacts known are African, as are many of the oldest megaliths, around 10,000 of which dot the Sahara and whose orientations are astronomical in character. We then briefly survey some of the creation stories and sky myths from a number of the peoples of sub-Saharan Africa. Finally, we turn to a few of the more unique calendars in the region.2023-05-1051 minThe Song of UraniaThe Stars in StoneWe turn the clock back to the astronomy of the Paleolithic and Neolithic. Clues about humanity's interest in the heavens during the Paleolithic can be seen in linguistic, mythological, and archaeological evidence. In the Neolithic, groups of people constructed tens of thousands of megaliths across Europe, many of which had astronomical connections.2023-04-0753 minThe Song of UraniaAstronomicaIn this episode we examine the work of two Roman astrologers to see how Roman astrology worked in practice: Marcus Manilius, who wrote Astronomica, and Firmicus Maternus, who wrote the Matheseos.2023-03-1155 minThe Song of UraniaMatters of Life & Death in Roman AstrologyAs Rome expanded to the East, the cultural influence of the Greeks deepened, and this included a strong interest in astrology. Despite resistance from conservative Romans, by the Imperial Era, astrology played a critical role in Roman politics, both as a tool to support conspirators attempting to assassinate emperors, and wielded by emperors as a way to eliminate challenges to their power.2023-02-101h 15The Song of UraniaThe Stars of BethlehemThis month the full moon falls on Three Kings' Day, traditionally a day that celebrates the adoration of the magi, so we investigate the famous Star of Bethlehem story. Through the centuries there have been dozens of astronomical and astrological theories put forward as to what the Star of Bethlehem was. We look at a few of the more prominent theories and their shortcomings, finishing with what is plausibly the leading candidate, the astrological theory of Michael Molnar, though as we'll see, this explanation, too, is not without its problems.2023-01-071h 08The Song of UraniaEtruscan & Roman AstronomyRome, the great empire of the Mediterranean, is not known for its astronomy. But while it lagged behind other civilizations, it is a mistake to think that they were entirely uninterested in the subject. Astronomical references permeated the Roman calendar and one of Rome's longest lasting contributions to Western civilization, the Julian calendar, was devised by the Roman astronomer Sosigenes.2022-12-081h 04The Song of UraniaThe Culmination of Ancient Greek AstronomyDuring the half millennium of the Roman Era in Ancient Greece, only two astronomers made any major advances. At the beginning of the Roman Era, Posidonius measured the size of the Earth and discovered the relationship between the Moon and the tides. But the triumph of Greek astronomy came 300 years later with the intricate planetary model of Ptolemy, which stood unchallenged for some 1400 years.2022-11-111h 11The Song of UraniaThe Antikythera Mechanism & FriendsIn the year 1900 a team of sea sponge divers stumbled upon a shipwreck from the late Hellenistic Era. Among the statues, coins, and jewellery, the salvage crew pulled out a small box covered in moss. Initially ignored, the contents of this box proved to be the most sophisticated mechanical device that survives from the ancient world. The Antikythera mechanism computed all the known motions of the heavens and its complexity was described by one scholar as "like finding a jet engine in King Tut's tomb."2022-10-1056 minThe Song of UraniaHipparchus the GOATAfter briefly examining the astronomy of Timocharis and Aristyllus, who developed the first known stellar catalog, we turn our attention to Hipparchus, who I claim was the greatest astronomer of ancient times. Hipparchus made major developments in virtually every area of astronomy known to him. His measurement of the lengths of the year and month were of unprecedented accuracy, he measured the distance to the Moon, and he developed a star catalog that was an order of magnitude larger than the earlier catalog of Timocharis and Aristyllus, which he was able to use to discover the precession of the...2022-09-121h 09The Song of UraniaThe Theory of Epicycles & DeferentsIn the Hellenistic Era the astronomer Apollonius of Perga (maybe) developed the model of epicycles and deferents that was to dominate Western astronomy for more than 1500 years. Around the same time, Eratosthenes, who was the head librarian at the Library of Alexandria, developed a novel technique to measure the circumference of the Earth and arrived at a suspiciously accurate result.2022-08-1347 minThe Song of UraniaThe Forerunners of CopernicusAt the dawn of the Hellenistic Age, two Greek astronomers developed radical new cosmologies. Heraclides of Pontica proposed that the Earth rotated on its axis and that Mercury and Venus revolved around the Sun instead of the Earth. Aristarchus of Samos went further and proposed that all the planets, including the Earth, revolved around the Sun. In addition, Aristarchus made the first quantitative measurement of the distances to the Sun and the Moon, along with their sizes.2022-07-131h 05The Song of UraniaAristotle, Plato's Other StudentTwo of Plato's students were notable astronomers. We looked at one of them, Eudoxus, in the last two episodes. In this episode we turn to Plato's other student, Aristotle. Aristotle embellished Eudoxus's model of planetary motion, but also developed a comprehensive physics and cosmology that ultimately became the standard model of the universe during the High Middle Ages.2022-06-151h 17The Song of UraniaThe Attic Calendar and its DiscontentsWe turn back the clock and see how a variety of Greek astronomers over the centuries contributed to the Greek calendar, and how Greek politicians ignored their developments. Then we see how the discovery that the seasons are not of equal lengths posed a problem for Eudoxus's theory of planetary motion.2022-05-1759 minThe Song of UraniaThe Homocentric Spheres of EudoxusIn working on the problem of doubling the cube, Plato's friend Archytas devised an ingenious solution that involved a three dimensional curve determined by the intersection of a torus with a cylinder. Archytas's student Eudoxus then seems to have been inspired by this solution to develop the first serious model of planetary motions in ancient Greece, his theory of homocentric spheres.2022-04-181h 00The Song of UraniaOn Plato's Broad ShouldersBefore leaving the world of the Pre-Socratics, we look briefly at the astronomy of Oenopides, which had a more observational character than many of his contemporaries. Then we turn to Plato, the first of the great astronomers in the Socratic tradition, whose astronomy synthesized the best ideas of his predecessors.2022-03-221h 09The Song of UraniaThe Atomic PhilosophersTwo philosophers, Leucippus and Democritus, attempted to synthesize the monist theories of the earlier natural philosophers with the pluralist theories of Empedocles and Anaxagoras. To do this, they proposed a revolutionary idea — that all matter is made of atoms.2022-02-1752 minThe Song of UraniaEx Uno, PluraAs we transition from the Archaic Period of Greece to the Classical Period, two philosophers, Empedocles and Anaxagoras, rebel against the prevailing dogma of monism and present a new idea — that matter consists of mixtures of multiple fundamental elements.Thanks to William Little of Ohio State for help with the Latin to get the opposite of "E pluribus unum" for the title.If you would like to register for the Stellar Spectacles symposium that I mentioned at the beginning of the episode, go to www.asxsociety.com.2022-01-2052 minThe Song of UraniaThe Eleatic School & the Way of TruthinessAfter the Median invasion, the Ionian philosopher Xenophanes, a student of the Anaximander, was forced to flee to Elea in Magna Graecia and brought the philosophy of the Ionians to the Eleans. His student, Parmenides, then founded the Eleatic School, which was skeptical of the senses, and argued that despite its appearance to the contrary, the Earth was round. Parmenides's student, Zeno, in turn developed his famous paradoxes to prove his teacher's assertion that motion was an illusion.2021-12-211h 03The Song of UraniaThe So-Called PythagoreansWe turn to the enigmatic, charismatic philosopher Pythagoras and the following that he inspired. Though Pythagoras is today associated with the Pythagorean theorem, he developed a school whose secrets were jealously guarded. The Pythagoreans studied astronomy, mathematics, and music, but also developed a unique philosophy centering around numbers that heavily influenced Plato.2021-11-241h 19The Song of UraniaThe Ionian SchoolMiletus became a wealthy Greek city during the Archaic Period and developed a thriving intellectual culture which included many of the most important pre-Socratic astronomers. We looked at Thales in the last episode and now we try to understand the astronomy of other members of the Ionian School — Anaximander, Anaximenes, and Heraclitus. What did their astronomy have in common with each other and what are the connections between their ideas and the ideas of modern physics?2021-10-2052 minThe Song of UraniaThales, through a Glass DarklyThales was the first of the Greek astronomers and became known as one of the Seven Sages of Greece. Over the centuries many astronomical discoveries were attributed to him, but what was the reality and what was the hyperbole?2021-09-221h 01The Song of UraniaThe Bards Sing of the SkiesWe outline the early development of Greek civilization after the Late Bronze Age Collapse and how the unique geography of Greece influenced its culture, and ultimately, its astronomy. Then we explore the cosmology, cosmogony, and astronomy of the earliest Greeks based on the works of Homer and Hesiod.2021-08-2350 minThe Song of UraniaGreek Tales of Ancient Nights & DaysAs we start to examine the astronomy of Ancient Greece we hear of the myth cycles of Theseus and Perseus, episodes from both of which appear in the night sky. These myth cycles help us to understand the conception the ancient Greeks had to the civilizations that came before them, the Minoans and the Mycenaeans and prepare us for the early cosmology of ancient Greece.2021-07-2453 minThe Song of UraniaSystem of a BWe dive into the most sophisticated model of planetary and lunar motions that the Babylonians developed: System A and System B and see how the Babylonians used this method to predict eclipses, the length of months, and even measure the precession of the perihelion.2021-06-2539 minThe Song of UraniaA System of Weights & MeasuresWe look at how the Babylonians represented information in their astronomical tablets by examining their number system and the unit system. Then we dive into the Babylonian discovery of the Saros cycle, which was a deep regularity in the pattern of lunar eclipses.2021-05-2742 minThe Song of UraniaThe Astronomical DiariesWe step back and look at Babylon's broader political history and see how Babylonian astronomy changes during the rise of the Neo-Babylonian Empire and the Persian Conquest. Then we look at some of the types of astronomical records the Babylonians produced, particularly the Astronomical Diaries, the longest continuous research program of any society in history.2021-04-2751 minThe Song of UraniaWhen the Moon DisappearsWe look at how the Babylonians associated the heavens with their gods and how Mesopotamian astrology developed after the Assyrian conquest. We hear some examples of astrological omens and see how Babylonians handled the most malevolent of omens, the lunar eclipse.2021-03-2942 minThe Song of UraniaThe Stars over BabylonWhat are the earliest records of constellations? How did the ancient Babylonians keep track of their progress through the year? And how do we know what we know about Babylonia?2021-02-2845 minThe Song of UraniaThe Heavens & HistoryHow should we approach the history of astronomy? How have the questions that astronomers have asked changed through the ages? We look at some of these questions and sketch out the broad arc of this field from antiquity to the present day.2021-01-2930 min