The Historic Discussion of Ptolemy’s Star Catalog

A page from the star catalog in a 1515 printing of Ptolemy's Almagest.
A page from the star catalog in a 1515 printing of Ptolemy's Almagest.

From the time of its writing in the 2nd century CE, Claudius Ptolemy’s Almagest stood at the forefront of mathematical astronomy for nearly 1,500 years. This work included a catalog of 1,025 stars, listing their coordinates (in ecliptic longitude and latitude) and brightnesses. While astronomers within a few centuries realized that the models for the sun, moon, and planets all had issues (which we today recognize as being a result of them being incorrect, geocentric models relying on circles and epicycles instead of a heliocentric model with elliptical orbits), the catalog of stars was generally believed to be correct.

That was, until the end of the 16th century, when the renowned observation astronomer Tycho Brahe realized that there was a fundamental flaw with the catalog: the ecliptic longitudes were low by an average of 1 degree.

What’s more, Brahe proposed an explanation for why. He suggested that Ptolemy had stolen the data from the astronomer Hipparchus some 250 years earlier, and then incorrectly updated the coordinates.

The question of whether this was a cosmic coincidence or the oldest case of scientific plagiarism is a question that historians of astronomy have argued for over 400 years.

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The First Stars May Have Weighed More Than 100,000 Suns

The first stars
A visualization of what the universe looked like when it was going through its last major transformative era: the epoch of reionization. Credit: Paul Geil & Simon Mutch/The University of Melbourne

The universe was simply different when it was younger. Recently astronomers have discovered that complex physics in the young cosmos may have led to the development of supermassive stars, each one weighing up to 100,000 times the mass of the Sun.

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Drag Sail Success! This Satellite Won't Turn Into Space Junk

The deployment of the Drag Augmentation Deorbiting System (ADEO) was captured by a camera onboard the ION satellite carrier. Credit: ESA.

The European Space Agency successfully tested a solar-sail-type device to speed up the deorbit time for a used cubesat carrier in Earth orbit.  The so-called breaking sail, the Drag Augmentation Deorbiting System (ADEO) was deployed from an ION satellite carrier in late December 2022. Engineers estimate the sail will reduce the time it takes for the carrier to reenter Earth’s atmosphere from 4-5 years to approximately 15 months.

The sail is one of many ideas and efforts to reduce space junk in Earth orbit.   

“We want to establish a zero debris policy, which means if you bring a spacecraft into orbit you have to remove it,” said Josef Aschbacher, ESA Director General.

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Good News! Webb is Fully Operational Again

Artist image of JWST in space. Credit: NASA

The James Webb Space Telescope is back to full science operations. One of the telescope’s instruments, the Near Infrared Imager and Slitless Spectrograph (NIRISS) had been offline since January 15 due to a communications error. But engineers worked through the problem and were able to return the instrument to full operations. 

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Soon Every Spacecraft can Navigate the Solar System Autonomously Using Pulsars

If you want to know where you are in space, you’d better bring along a map. But it’s a little more complicated than riding shotgun on a family road trip.

Spacecraft navigation beyond Earth orbit is usually carried out by mission control. A series of radio communication arrays across the planet, known as the Deep Space Network, allows operators to check in with space probes and update their navigational status. The system works, but it could be better. What if a spacecraft could autonomously determine its position, without needing to phone home? That’s been a dream of aerospace engineers for a long time, and it’s getting close to fruition.

Pulsars are the key.

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Astronomers Come Closer to Understanding How Mercury Formed

Artist's concept of the MESSENGER spacecraft on approach to Mercury. Credit: NASA/JPL

Simulations of the formation of the solar system have been largely successful. They are able to replicate the positions of all the major planets along with their orbital parameters. But current simulations have an extreme amount of difficulty getting the masses of the four terrestrial planets right, especially Mercury. A new study suggests that we need to pay more attention to the giant planets in order to understand the evolution of the smaller ones.

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Rolls-Royce Reveals a Nuclear Reactor That Could Provide Power on the Moon

For space agencies and the commercial space industry, the priorities of the next two decades are clear. First, astronauts will be sent to the Moon for the first time since the Apollo Era, followed by the creation of permanent infrastructure that will allow them to say there for extended periods. Then, the first crewed missions will be sent to Mars, with follow-up missions every 26 months, culminating in the creation of surface habitats (and maybe a permanent base). To meet these objectives, space agencies are investigating next-generation propulsion, power, and life support systems.

This includes solar-electric propulsion (SEP), where solar energy is used to power extremely fuel-efficient Hall-Effect thrusters. Similarly, they are looking into nuclear thermal propulsion (NTP) and compact nuclear reactors, allowing for shorter transit times and providing a steady power supply for Lunar and Martian habitats. Beyond NASA, the UK Space Agency (UKSA) has partnered with Rolls-Royce to develop nuclear systems for space exploration. In a recent tweet, the international auto and aerospace giant provided a teaser of what their “micro-reactor” will look like.

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Astronomers Detect a Second Planet Orbiting Two Stars

Artist's impression of Kepler-16b, the first planet known to definitively orbit two stars - what's called a circumbinary planet. The planet, which can be seen in the foreground, was discovered by NASA's Kepler mission. Credit: NASA/JPL-Caltech/T. Pyle

Planets orbiting binary stars are in a tough situation. They have to contend with the gravitational pull of two separate stars. Planetary formation around a single star like our Sun is relatively straightforward compared to what circumbinary planets go through. Until recently, astronomers weren’t sure they existed.

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Don’t Bother Trying to Destroy Rubble Pile Asteroids

Detailed view of the rubble-pile asteroid 25143 Itokawa visited by the Japanese spacecraft Hayabusa in 2005. Credit: JAXA

The asteroids in our Solar System are survivors. They’ve withstood billions of years of collisions. The surviving asteroids are divided into two groups: monolithic asteroids, which are intact chunks of planetesimals, and rubble piles, which are made of up fragments of shattered primordial asteroids.

It turns out there are far more rubble pile asteroids than we thought, and that raises the difficulty of protecting Earth from asteroid strikes.

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Watch This 12-Year Timelapse of Exoplanets Orbiting Their Star

Four faint exoplanets orbit star HR8799, which is represented by a star-shaped icon in the center. (The star itself was removed from the video because its glare is so intense that it blocks out the surrounding planets.) Credit: Jason Wang/Northwestern University.

Back in 2008, astronomers made a big announcement: for the first time, they had taken pictures of a multi-planet solar system, much like ours, orbiting another star. At the time, the star system, named HR8799 was known to have three planets, but follow-up observations a year later revealed a fourth world.

Astronomers have continued to watch this intriguing star system, and now, using observations from the last 12 years, astrophysicist Jason Wang has put together a time lapse video showing the orbital motions of the four planets.

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