Articles on the myriad topics within Astronomy, written by yours truly.
An Amateur Astronomer’s dream come true.
19 October, 2023
An edited (by the Editors at The Hindu) version of this was later published in the Chennai Edition of The Hindu, print and online. Here’s the original written by me:
It was freezing at sub-zero temperatures. The conditions were unforgiving. And we were elated and thrilled being outdoors all night.
At 4300 metres above sea level, we felt it could’ve been the Everest Base Camp. In reality, we were at Hanle, UT-Ladakh. The air is so thin at such altitudes that oxygen levels are less than 60% of what are normally used to at sea level. In fact, we had to acclimatise for 48 hours at Leh (3500m) before climbing up to Hanle. It is definitely not for everyone. So why did a bunch of us go up there, and stay outdoors at sub-zero temperatures for 3 nights in a row? We were a select group of amateur astronomers invited by the Indian Institute of Astrophysics (IIA) to attend the HDSR Star Party 2023, organised and conducted by IIA.
The Hanle Dark Sky Reserve (HDSR) is India’s first dark sky region, and is centred at Hanle in Eastern Ladakh around the Indian Astronomical Observatory (IAO). HDSR preserves the dark skies by reducing light pollution in the surrounding areas and uses these dark skies to promote Astrotourism as a means to further enhance socio-economic development in the area.
What is a Dark Sky?
A dark sky is the night sky as nature meant for it to be: without light pollution. Man-made lights that we use, especially outdoor lights, block our view of stars and most celestial objects in the night sky.
What can we see in a Dark Sky?
Ironically, a dark sky lets you see better. From a light-polluted city, we can typically see only a handful of stars. However, from a dark site, we can see thousands of stars. Apart from stars, the Milky Way’s galactic centre and arms are clearly visible to the naked eye. We can see several star clusters, nebulae, galaxies such as Andromeda and Triangulum, as well as Zodiacal Light (a faint glow of diffuse sunlight scattered by interplanetary dust in the Solar System), Airglow (an optical phenomenon caused by faint emission of light in the Earth’s atmosphere), and Gegenschein (a bright spot in the night sky centered at the antisolar point, caused by backscatter of sunlight by interplanetary dust). Venus can be so bright in the night sky that its light can cast shadows on the ground, just as moonlight does.
Although some of us were theoretically aware of these optical phenomena as well as the fact that we could see so many stars and celestial objects under the darkest of skies, it was still an overwhelming feeling to actually observe and experience them under the Bortle Class 1 skies of Hanle.
Bortle Scale
The Bortle Scale helps amateur astronomers measure the night sky’s brightness of a given location. The scale ranges from Class 1, the darkest skies available on Earth, through to Class 9, inner-city skies.
A sense of thrill as well as caution filled the thin air under the dark skies of Hanle. Observing outdoors in these harsh conditions, with or without equipment, one had to be both strong-willed and careful. But it was worth every second as caution led to exhilaration and wonder.
For us amateur astronomers, the 3 nights (and days) of the HDSR Star Party made for a great opportunity to not only observe from the pristine night skies, but also connect with fellow amateur astronomers who had come from various parts of the country – experienced amateurs as well as young ones with starlit eyes. Rubbing shoulders with professional astronomers, exchanging ideas and information on all things astronomy – Visual Observation, Astrophotography – as well as sharing huge telescopes and imaging equipment during the event made for an unforgettable experience.
A great start to something big.
Being the first ever Dark Sky Reserve of the country, HDSR is certainly a source of pride for India and will be a blueprint for other dark sites in other regions. Just like at Hanle, upcoming dark sky reserves can promote Astrotourism, which will help both amateur astronomers like us as well as local communities. Highly likely to evolve into an annual event, I’m glad I was part of the successful first edition of HDSR Star Party this year, expertly and thoughtfully planned and conducted by Mr. Dorje Angchuk, the Engineer-in-Charge at the Indian Astronomical Observatory, Hanle and Mr. Niruj Mohan Ramanujam, Head, IIA SCOPE Section. I believe the event was a great start to something big for casual stargazers, passionate amateur astronomers, and our space-loving country as a whole.
Busting the Pink Moon, the Blue Moon, and other Moons.
6 April, 2022
Ok, people. A Pink Moon doesn’t look pink, and a Blue Moon doesn’t look blue. Pink Moon, Flower Moon, Buck Moon, Hunter’s Moon, etc. are merely names given according to seasonal changes in the environment observed by early humans and civilisations.
For example, the Pink Moon (Full Moon of April) derives its name not from the Moon’s appearance or colour, but from the seasonal flowering of moss pink flowers, also called perennial wild ground phlox. The Moon doesn’t actually look pink. Similarly, the Full Moon of May is called Flower Moon as flowers are in full bloom. Yes, the Moon doesn’t look like a flower either. Buck Moon (Full Moon of July) gets the name from male deer (Bucks) regrowing their antlers in summer (having shed them in winter), getting ready for the autumn breeding months. Needless to say, the Moon doesn’t look like deer. Hunter’s Moon (Oct) is named in the Native American tradition as the best time to hunt and stock up on food for the upcoming winter as the Full Moon gives enough light to hunt even after sunset.
As for the Blue Moon, the thirteenth Full Moon of a year is called a Blue Moon. Another definition of the Blue Moon is the third full moon in a season with four full moons (it’s usually only three Full Moons per season). This helps correct the timing of the last month of a season that would have otherwise been expected too early. This happens only every two to three years, and this rarity gives rise to the usage “Once in a blue moon”.
A common (mistaken) definition of a blue moon.
Another definition of the blue moon, perhaps the more commonly used due to its simplicity, is actually a mistake, made in the 1940s and perpetuated by radio shows and the Trivial Pursuit board game through the 1980s. This definition describes the blue moon as the second full Moon in any calendar month with two full moons. 1
While Blue Moons don’t look blue, the Moon can sometime appear blue (whether full or not) under certain specific atmospheric conditions such as volcanic eruptions or fires that release particles into the atmosphere that filter or scatter the other longer (yellow-orange-red) wavelengths of light and only the shorter (blue) wavelength reaches our eyes, making the Moon appear blue.
Now that we’ve busted some Moon myths, the next time someone shows you a photo of the Moon that looks pink, you know what to do.
1 Ref: Royal Museums Greenwich rmg.co.uk
An Extragalactic Exoplanet has possibly been detected for the first time.
Astronomers have identified evidence for a possible planet outside of the Milky Way galaxy using NASA’s Chandra X-ray Observatory.
27 October, 2021
A temporary dimming in X-rays in a binary system was detected by the Chandra Observatory. Researchers interpret this dimming as a planet passing in front of an X-ray source around a neutron star or black hole orbiting a companion star.
Therefore, this detection is considered as evidence for a possible planet candidate in the M51 galaxy, also known as the Whirlpool Galaxy, potentially representing what would be the first planet seen to transit a star outside of the Milky Way – an Extragalactic Exoplanet. Researchers used NASA’s Chandra X-ray Observatory to detect the dimming of X-rays from an “X-ray binary”, a system where a Sun-like star is in orbit around a neutron star or black hole. The authors interpret this dimming as being a planet passing in front of the neutron star or black hole.
Credit: NASA/CXC/M. Weiss
This method of detecting an exoplanet orbiting a star is known as the Transit Technique. When a planet passes directly between its star and the observer, it dims the star’s light by a measurable amount. This not only provides evidence of the presence of an exoplanet, but also of the size and number of planets orbiting the star. Amongst the 5 methods astronomers use to detect exoplanets, the Transit Technique has been the most prolific, yielding 3428 exoplanet detections so far.
For several years, if not decades, astronomers have discovered exoplanets using transits with optical light telescopes, which detect the range of light humans can see with their eyes and a bit more. This includes both ground-based telescopes and space-based ones like NASA’s Kepler mission. These optical light transit detections require very high levels of sensitivity because the planet is much smaller than the star it passes in front of, and, therefore, only a tiny fraction of the light is blocked.
However, a transit in an X-ray binary is different. This is because a potential planet is very similar in size to the X-ray source around the neutron star or black hole, a transiting planet passing along Earth’s line of sight could temporarily block most or all of the X-rays. This makes it possible to spot transits at greater distances — including beyond the Milky Way — than current optical light studies using transits. The graphic below shows how X-rays from M51-ULS-1 temporarily decrease to zero during the Chandra observations.
“We are trying to open up a whole new arena for finding other worlds by searching for planet candidates at X-ray wavelengths, a strategy that makes it possible to discover them in other galaxies,” said Rosanne Di Stefano of the Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge, Massachusetts, who led the study, which was published in Nature Astronomy.
If a planet exists in this system, it likely had a tumultuous history and violent past. An exoplanet in the system would have had to survive a supernova explosion that created the neutron star or black hole. The future may also be dangerous. At some point the companion star could also explode as a supernova and blast the planet once again with extremely high levels of radiation.
While this is a tantalizing study with highly exciting possibilities, the case of an exoplanet in M51 is not ironclad. At least not yet. One challenge is that the planet candidate’s large orbit in M51-ULS-1 means it would not cross in front of its binary partner again for about 70 years, thwarting any attempts for a confirming observation for decades. There is also the possibility that the dimming of X-rays is due to a passing cloud of gas near the M51-ULS-1, though the researchers think the data strongly favor the planet explanation.
Info Credit & References: NASA, Chandra X-Ray Observatory, DiStefano, R., et al., 2021, Nature Astronomy
A cosmic alignment helps free a stuck ship.
The Sun, Earth, and Moon fall in line, help free a ship that is grounded on the Suez Canal.
2 April, 2021
Why are we writing about a ship on Spacewards? What does the Moon have to do with a ship that was stuck in the Suez Canal?
Firstly, a little background on the ship situation. A humongous container ship, called ‘Ever Given’, got pushed sideways (seen in the image above) by winds and got stuck in the sandy clay on the banks of the Suez Canal in Egypt. This completely blocked traffic from either direction as the canal is not only narrow, but it was also in a single laned part, which was shared by ships travelling in both directions. Being one of the busiest sea routes, this meant a huge logjam of ships on either side of the canal stretching for up to a 100km, as can be seen below in these photos of the Gulf of Suez, located south of the canal, captured from space.
Now, what does this have to do with the Moon? What has Astronomy got to do with clearing a traffic jam of giant ships in the seas? A lot, apparently. Now the ship has been freed from the sandy banks, thanks to multiple forces at work. The human contribution has been immense, of course. Excavators helped remove the sandy clay from around the ship’s bow and multiple tugboats pulled the ship away from the shore. However, the contribution of Astronomy is what we are interested in, here.
The relationship between ships and astronomy is pretty well-known, even more so to sailors in the olden days. Knowledge of the stars, constellations, and tide patterns have aided seafarers ever since humans set out to sea. Tides, among these, is what has contributed to the freeing of the stuck ship. Although high tides and low tides each occur twice every day (approximately every 24 hours and 50 minutes – called a lunar day), this particular tide cycle that helped free Ever Given has more to it. Let’s dig deeper, pun unintended.
The rising and falling of the sea during high tide and low tide, respectively, is an everyday occurrence that was going to help in dislodging the massive vessel. However, the tides were extra special in the days leading up to the freeing of the ship, known as a Perigean Spring Tide. Simply put, a Perigean Spring Tide occurs when the moon is either new or full and is closest to Earth in its orbit. Let’s look at a few facts that will help understand this phenomenon better.
Tides
Tides, the common ones, are caused by the gravitational pull of the Moon and the Sun. Tides are actually long-period waves that roll around the planet as the ocean is ‘pulled’ back and forth as the Moon and the Sun interact gravitationally with the Earth during the Moon’s monthly orbit around the Earth and Earth’s yearly orbit around the Sun. The tidal forces of the Moon are much stronger, about twice as strong as the Sun, as it is much closer to the Earth.
Tidal ranges during a New or Full Moon
The Earth, Moon, and Sun, are nearly in alignment twice each lunar month (~29.5 days on average). The moon appears new (dark) when it is between the Earth and the Sun. The moon appears full when Earth is between the Moon and the Sun. During New and Full Moons, average tidal ranges are slightly larger. During both times, being in an almost straight line, the gravitational pull of the Sun gets combined with that of the Moon on Earth, causing the oceans to bulge a bit more than usual. This means that high tides are higher and low tides are lower than average. These are called Spring Tides. Nothing to do with the season, just the ‘springing forth’ of the tide.
The Effect of Perigee
In its orbit around the Earth, once every ~28 days, the Moon reaches Perigee, its closest point of approach to the Earth, popularly known as Supermoon. Thanks to its proximity to Earth, the gravitational pull of the Moon is strongest when at Perigee. During this period, the average range of tides increases. Conversely, about 14 days following Perigee, the moon reaches Apogee, its furthest point of approach to the Earth, popularly called Micromoon. Consequently, the gravitational pull of the moon is at its weakest at Apogee. And the average range of tides decreases.
Tidal ranges during a New or Full Moon at Perigee
What happens when a New or Full Moon coincides with Perigee? Take a look at the image from NOAA above. You’re probably thinking right. The effects get added up. The New or Full Moon coincides with the Perigee of the Moon typically 6 to 8 times a year. And when this happens, the tidal ranges are even larger. This phenomenon is called a Perigean Spring Tide. The difference between Perigean Spring Tides and Spring Tides that occur closer to the moon’s Apogee can be quite substantial. Depending on the location on Earth, high tides during Perigean Spring Tides can be a foot to three feet higher than high tides during Apogean Spring Tides.
The Perigean Spring Tide caused by the Full Moon of March 2021
Back to the Suez Canal. The massive cargo ship, Ever Given, had been stuck across the canal since 23rd March, when a seasonal sandstorm known as a khamsin buried the ship’s bow 16 feet into the soil. As the excavators were digging away, removing soil from around the bow, and tugboats pulling Ever Given away from the bank of the canal, the tides were getting stronger with each passing day. Since the Moon was approaching Perigee on 30th March, the Full Moon on the night of 28th-29th March ensured the effect of the Perigean Spring Tide caused the low tide low enough for further digging around the bow early in the morning of the 29th, and the following high tide about 6 hours later was high enough to help float the ship. Commenting on the developments, Nick Sloane, a maritime salvage expert, said the few additional inches brought by the spring tides made a critical difference, adding thousands of tons of buoyancy to float the Ever Given.
This whole saga stands testimony to the fact that, whether we are aware or not, astronomical phenomena are happening all the time and influencing our everyday lives in a profound and inextricable way.