— by Arnab Gupta

☞ Recent ISRO satellite launch carried special imaging constellation

February 27, 2017

From the website of the company ‘Planet’, published the same day the ISRO satellites were launched:

Today Planet successfully launched 88 Dove satellites to orbit — the largest satellite constellation ever to reach orbit. This is not just a launch (or a world record, for that matter!); for our team this is a major milestone. With these satellites in orbit, Planet will reach its Mission 1: the ability to image all of Earth’s landmass every day.

This constellation therefore formed the majority (88 of 104 satellites launched) of the payload carried by the last ISRO launch. As of this launch, Planet is operating 149 satellites in Earth orbit — this is no mean feat.

Also, an interesting side note: ISRO’s previous largest payload that I referred to in my last post — 20 satellites launched in June 2016 — also seems to be for this same company:

This is our 15th launch of Dove satellites and second aboard India’s PSLV. The launch of Flock 3p comes off the successful launch of Flock 2p on the PSLV in June 2016

☞ Indian Space Research Organization launches satellites, breaks record

February 15, 2017

Indian Space Research Organisation (ISRO) scripted history today by successfully launching a record 104 satellites, including India’s earth [sic] observation satellite, on a single rocket from the spaceport in Sriharikota. This is the highest number of satellites ever launched in a single mission.

The previous record was held by Russia, with 37 satellites launched at one go. The 104 satellites include 3 of India’s own and 101 of ISRO’s international customers, including 96 from USA. (The article states ISRO’s previous record as 23 satellites launched together in June 2015, but I can’t find a record for that. The closest I could find was this: 20 satellites launched in June 2016.)

As much as this is making news, and as much as ISRO should be proud, this should come as no surprise for space enthusiasts— ISRO has been quite a force in space technology, especially using its PSLV launch system, for quite some time now.

The four stage Polar Satellite Launch Vehicle (PSLV), used for this launch, was developed by ISRO in the 1990s to launch satellites into Sun-synchronous orbits for its own remote sensing satellites. (Other than ISRO, only Russia commercially launches satellites into Sun-synchronous orbits.) PSLV was also used by ISRO for Chandrayaan 1, its lunar probe, and Mangalyaan, its Mars orbiter, becoming only the fourth space agency to reach Mars orbit.

As an aside, the Sun-synchronous orbit is a very interesting concept: it is an orbit where the satellite passes over any given point on Earth’s surface at the same local solar time. This allows the satellite to be in constant sunlight as it passes over particular regions— which is great for imaging, remote sensing, spying and weather applications. The technicalities of such an orbit are very involved and very interesting: look up the Wikipedia page I’ve linked to above.

Fun fact: due to the mechanics of the orbit, a sun-synchronous orbit is stable without external thrust only on oblate spheroid planets. This means that such orbits work on Earth and will work on Mars, but on almost spherical planets such as Venus, it will require external thrust to maintain its orbit.

☞ Hydrogen map of the sky to show the Sun’s motion in the galaxy

November 02, 2016

I know this can be hard to picture in your head, but the beauty of it is that once you do, this map sings. You can instantly see what’s what: the motion of the gas, where it’s more dense than other locations, how it’s distributed. It also shows our location in the galaxy! All those changing velocities depend on the Sun’s velocity, the velocity of the gas, but also the direction of the Sun’s motion and its position in the Milky Way’s disk. That’s a stunning amount of information.

This is fascinating.

Of Alien Megastructures

October 28, 2016

They call it Tabby’s star. It is a main sequence star quite similar to our Sun, and is about 1500 light years away from us, in the region of the constellation Cygnus. And it’s a particularly odd one. It was studied using the Kepler Space Observatory, which is the space telescope used for identifying planets orbiting distant stars. All of the exoplanet discoveries in the news over the past few years is due to Kepler.

To understand what’s odd about Tabby’s star, we need to know how Kepler operates. What it does is measure — very accurately — the apparent brightness of stars over time. If the apparent brightness of a star changes, that data is used to find patterns in how much and when the brightness changes occur.

Consider what happens with a planet revolving around a star. The apparent brightness of the star dips every time the planet passes in front — i.e. to observers here on Earth — of the star, and the amount and duration of the dip correlates with the size and velocity of the planet. This process works well, and has helped in the discovery of many, many exoplanets revolving around numerous star systems.

Now that we know the basics, here’s why Tabby’s star is so intriguing. Tabby’s star shows small dips in brightness that are both frequent and non-periodic. It has also shown two large recorded dips separated by two years time. How large are the large dips? Where a Jupiter sized planet would have obstructed the star by about 1%, the large dips obscure the star by as much as 15% to 22%. Whatever is blocking the star light during the major dips is not a planet — it is obscuring almost half the width of the star.

That’s not all. It turns out, even without the obscuring, the light output from Tabby’s star seems to be diminishing over time. It turns out, we have observational data about this star since 1890 (via numerous photographs that contain this star in the image), and it seems to have faded by 20% from 1890 to 1989! Even if such old and long-term data is deemed inaccurate, Tabby’s star has definitely diminished in the recent past, in the era of modern measurements. It seems to dim at a slow steady rate, with one short period of a more dramatic fading.

What could be causing such behavior? A number of hypotheses have been proposed, but none of them fully explain the observations. Could it be a young star with coalescing planetary material floating around it? Nope; no such evidence found. Could there be debris from planets that have collided and created clouds of debris and dust? Nope; this is not supported by observations. Could it be a huge number of disintegrating comets orbiting the star? Nope: they wouldn’t obscure the star’s luminosity by as much as 22%.

Well, could it be aliens?

We on Earth are starting to realize how important it is to harness the Sun’s energy as much as we can. We as a civilization have already fantasized about the creation of a huge structure that captures solar energy from every direction, not just from Earth, and using that energy as our planetary energy needs soar. Such a structure is a sphere that “covers” the Sun, and is called a Dyson Sphere, after the scientist who wrote a paper about it in 1960.

Dyson speculated that such a structure would become inevitable as a civilization advances and its energy needs escalate. Realistically, of course, the “sphere” wouldn’t be an actual sphere (imagine how big the sphere would have to be, and how it would revolve around the Sun!), but a “swarm” of smaller objects revolving around the Sun, like satellites. Collectively, they would serve a similar purpose.

What if the observations of Tabby’s star are the tell-tale signs of an alien civilization building a Dyson Swarm? It would explain the long-term fading, and also the sharp dips in its brightness. It would not be a planet; it’d be an artificial mega-structure being slowly constructed. Such construction projects could very easily — by design — obscure 22% of the star’s luminosity.

It’s an idea, and it’s a pretty fantasy for earthlings in the infancy of space-flight, but this idea does have its caveat. An advanced civilization would most likely have a lot of radio signal emissions (we do too — our TV and radio signals are propagating into space at the speed of light) that we should be able to detect. The SETI (Search for Extra-Terrestrial Intelligence) project spent two weeks studying the star system in October 2015, but did not find any technology-related radio signals in multiple frequency spectra.

If you can’t contain your excitement about the possibility of alien life, you still have hope. Whatever the caveat, and however slim the chances, scientists have not been able to rule out this possibility. More studies are planned that will devote resources — including that of SETI — towards studying Tabby’s star and its surroundings, and we will know more in 2017. If they’re really an advanced alien civilization, for all we know, they might have decided (and have the capability) to stop their radio signals from propagating into deep space!

If you’re apprehensive about finding aliens capable of — and in need of! — harnessing all of its star’s energy, you still have hope. What are the chances? For all the advancements we have made in astronomy and the study of the heavens, we really do yet have a lot to learn. When we observe anomalous behavior through our telescopes, the anomaly is due to limitations in our technology or understanding. What are the chances that this is the one case where our knowledge is perfect and the observations are unnatural?

Either way, this is one star we are certain to keep in our sights. The next few years will tell us more — about how little we know about the stars, or about how we’re not alone in the universe.


  • This recent paper confirms that Tabby’s Star has faded throughout the duration of it being observed by Kepler. Other stars were also observed at the same time, and none of them fade at such a drastic rate. (doi:10.3847/2041-8205/830/2/L39)
  • The “Breakthrough Listen” project, backed by Prof. Stephen Fleming Hawking (oops, bad typo!) and funded by $100 million, will be used to observe Tabby’s star.

(This piece first appeared in the 2016 edition of Sharod Sombhar, an annual magazine from the Bengali Students’ Association at Virginia Tech.)

☞ A hermit crab changes home; brings house guests along

September 01, 2016

I’m always fascinated by documentaries about marine life, and I found this quite brilliant.

How the crab invites its house guests to come along to its new house is particularly interesting.

(I won’t say any more; go watch.)

☞ Britain has voted to leave the European Union

June 23, 2016

Britain has voted to leave the European Union, a historic decision sure to reshape the nation’s place in the world, rattle the Continent and rock political establishments throughout the West.

With 309 of 382 of the country’s cities and towns reporting early on Friday, the Leave campaign held a 52 percent to 48 percent lead. The BBC called the race for the Leave campaign shortly before 4:45 a.m., with 13.1 million votes having been counted in favor of leaving and 12.2 million in favor of remaining.

The value of the British pound plummeted as financial markets absorbed the news.

This is historic. Only time will tell whether the net effects will be good or bad — for Britain and for the European Union. (I haven’t followed the intricate details of the pros and cons, but I understand that the full effects and implications are hard to predict if only because the interactions and agreements between countries are so intertwined.)

P.S. — The following are required viewing:

Gallons per 100 Miles — The Calibration Chart

June 09, 2016

In the US, automobile fuel economy is usually measured in miles per gallon, mpg. This works, but there is a better metric, especially for comparison between values. Gallons per 100 miles is the way to go!

This is very well known, and even I’ve talked about this before. There are numerous online tools to do the conversion from mpg to gallons per 100 miles… but there don’t appear to be any simple conversion or calibration charts for it.

Well, here you are — an easy to use chart to convert between mpg and gallons per 100 miles (or, equivalently, from km/l to liters per 100km).