Another Blood(y) Moon!

Total Lunar Eclipse on 7Sep25

A few Native American tribes think that a moon turns red when it is deprived of love and care. Therefore, a blood moon meant that the moon needs affection.

 

 

The forthcoming total lunar eclipse on 7-8 September 25 affords another opportunity to witness a grand spectacle of Nature on a cosmic scale when the Earth’s shadow eclipses the Moon for a substantial period of time. Visible all over the country, it can be observed with nothing more than the naked eye.

 

Blood(y) Moon

This is a serious article with a flippant title, the kind that cries out for attention, actually for affection if the voice of the native American tribes is not taken facetiously. Both these feelings make sense when they are applied to the forthcoming total lunar eclipse on the night of 7-8 September 25.  Having said that, I must emphasize that the term ‘blood’ or ‘bloody’ (the latter is used very rarely and only colloquially!), invoking images of horror and fright, are shunned by most astronomers, including amateurs like me.  It is a description that our nearest celestial neighbor doesn’t befit any time. Only poets, soothsayers, storytellers and occultists are fond of it. The preferred, and technically correct, term is ‘copper-red’ (or ‘coppery red’ if you choose not to stick to King’s English). However, someone with dichromatic vision like me is not the type to offer any definitive judgment. Plain red will do for me. No blood need be shed on this count!

Be it as it may, avid night sky watchers are waiting for a great opportunity to see another total eclipse of the Moon on the night of Sunday, 7th September this year, just a few days from now.

Looking back

To the best of my recollection (lunar eclipses are not really high on my list of celestial wonders!), the last such eclipse occurred less than three years ago, on 8 November 22, and was a major ‘success’ from the visibility point of view.  In contrast, a previous one, on 10 December 2011, was a huge disappointment in most places because of cloudy skies most of the time, compounded by the late hour of the event which also discouraged most people. 

Some of my earlier blog posts relate to eclipses in general and solar eclipses in particular. My last two posts in June 2011 (see here and here) relate specifically to the total lunar eclipse of June 15-16 and the reader may like to go through both of them to set the stage for the forthcoming one.

How do eclipses happen

As pointed out in my earlier posts, solar and lunar eclipses as seen from the Earth would not have been possible at all but for a very fortuitous and remarkable circumstance relating to the three celestial bodies. The apparent sizes of the Sun and the Moon as seen by us on Earth just happen to be nearly the same, approximately half a degree in angular diameter. When the Earth comes between the Sun and the Moon as on a full moon day, the latter can be found in the shadow of the Earth and hence sunlight will not be falling on it directly.  This is when a lunar eclipse occurs.  As seen from any point on the Earth, the eclipse may be partial or total.  One might expect the Moon to be completely hidden from view during a total lunar eclipse.  However, the whole of the Moon can be seen clearly as a faint coppery red object because of sunlight scattered by the Earth’s atmosphere, predominantly in the red, falling on the lunar surface and thereby illuminating it.  It is a wonderfully beautiful sight to behold! Would it be fair to regard the Moon as truly eclipsed?

The diagram below shows the Moon berthed in the Earth’s shadow during a total lunar eclipse.

Eclipse of Sep 7-8

The forthcoming total lunar eclipse will occur when the Moon is situated within the (zodiacal) constellation Aquarius, as shown in the following chart generated with the Starry Night Pro Plus 8 astronomy software.  

The night sky is rich in several prominent constellations, particularly Andromeda, and the ringed planet Saturn is close by. The area is not particularly rich in bright stars. The square of the Pegassus is a great sight. Cassiopea will be positioned in the far north (on the left of the chart). One should also be able to make out the summer triangle of stars Vega, Deneb and Altair.

During the period of totality that lasts about 82 minutes, the night sky in that region should be beautiful, especially if the viewer is located well away from disturbing lights.  It should be so even from urban locations. However, there is a huge question mark about the weather. Even short breaks in cloud cover (over a period of about an hour starting from about 11 PM) will be enough to view the event in all its glory. Below is a table showing different phases of the event.  It is more or less the same everywhere in the country.

Event	Date	Time (IST)
Penumbral eclipse begins	7 Sep	8:58 PM
Partial eclipse begins	7 Sep	9:57 PM
Total eclipse begins	7 Sep	11:01 PM
Middle of totality	7 Sep	11:42 PM
Total phase ends	8 Sep	00:23 AM
Partial phase ends	8 Sep	01:26 AM
Penumbral phase ends	8 Sep	02:25 AM

The Moon's contact times with the Earth's umbral and penumbral shadows are shown in the following diagram.  The times shown are in Universal Time (UT).  Add 5:30 to obtain the local time (IST) anywhere in India. 

Event visibility

The following illustration, shows the visibility of the eclipse from any place on the Earth.  As is evident, the event can be seen in its totality from most parts of Asia and Australasia as well as many other regions. 

Cloud cover

Now, for the discouraging part. The following average cloud coverage map presents a rather disheartening picture.  Yet, if a previous event (see here) is any indication, most observers may still be able to see clear glimpses of the ‘blood’ Moon through occasional cloud breaks.

Mean afternoon cloud coverage in September (Courtesy: J Anderson)

Watching the Eclipse

In most parts of India, depending of course on the weather, sunset on 7th evening should be greeted by a bright and brilliant full Moon rising in the east.  One has to wait quite a long time, till about 9 PM, for the penumbral phase of the eclipse to begin.  For some time at least, it may be very difficult to notice even a slight decrease in the brightness of the Moon.  Only skilled observers may detect a faint shading across the lunar disk. This phase will last about an hour, until the Moon starts entering the umbral shadow of the Earth around 10 PM.  This marks the beginning of the partial phase of the eclipse.  Thereafter one should be able to see a progressive 'eating away' of the Moon's surface and a marked decline in brightness as the visible portion of the lunar surface shrinks. 

Around 11 PM, totality will set in when the whole of the lunar surface is inside the Earth's umbral shadow.  However, as already explained, the Moon continues to be visible as a faint copper-red disk.  This phase lasts the next 82 minutes, with small but noticeable variations in the overall brightness.  This is the time when the viewer can soak in a wonderful view of the night sky with a faint reddish full Moon appearing to be suspended like a friendly ghost with a smattering of stars all around.  A pair of binoculars would be a great visual aid to use at this juncture.

The total phase will end by 00:30 AM the following morning when the Moon should begin to shine in direct sunlight.  It should progressively grow brighter and restored very nearly to its full glory when the partial phase ends around 1:30 AM.  However, the Moon will remain in the penumbral shadow until around 2:30 AM (only some diehard observers may wait to see this happen).  This marks the end of what should be another memorable total lunar eclipse so soon after the last one a few years ago.

Unlike a solar eclipse where one has to take special precautions and safe filters to view the event, the Moon is a totally harmless object at any time, and especially so during an eclipse, no matter what the media may project.  The astrologers and soothsayers will no doubt have their usual field day with a highly gullible public willing to believe anything portentous and sensational and not caring for a scientific perspective of the event.

In the following map created from the interactive software designed by Xavier Jubeir, all the eclipse parameters for Mysore are presented for the technically inclined:

Photography

Lunar eclipse photography is easy, particularly with high zoom digital SLR cameras, and requires no special equipment or filters. However, a sturdy tripod is strongly recommended, especially during the total phase.  Since the whole event lasts quite a long time, photographs can be taken in a well-planned manner at regular intervals of time.  One may have to experiment with the exposure times because of the changing brightness of the sunlit part of the lunar surface as the eclipse progresses. It is best to set the aperture at maximum so that the exposure times can be minimized. 

With a zoom camera, the longest zoom setting will naturally give a much larger image than otherwise and should therefore be invariably preferred. With an ordinary (wide field) camera it would be interesting to capture the Moon in its natural setting, against the backdrop of interesting scenery in the foreground.  An interesting way to present the wide field pictures taken at regular intervals of time is to make a composite image for which a photo editing software package may come in handy.

Expected sequence of events

Here is a compact, sky-watcher’s timeline for Mysore on the night of Sunday–Monday, 7–8 September 2025 (IST) as suggested by ChatGPT:  

1. Face roughly ESE at the start, and follow the Moon as it climbs toward the south and then drifts SW.
2. 8:58 pm (Sep 7) — Penumbral shading begins. A subtle gray “smudge” creeps onto the Moon’s eastern limb. Alt ~36° up in the ESE.
3. 9:57 pm — Partial eclipse begins. A distinct “bite” appears as the Moon enters Earth’s umbra; dimming becomes obvious. Alt ~49°, ESE.
4. 11:00 pm — Totality starts. The Moon turns copper-red; stars around it pop into view. Alt ~62°, SE.
5. 11:41 pm — Maximum eclipse. Deepest color and darkest mid-eclipse. Alt ~69°, SSE.
6. 12:22 am (Sep 8) — Totality ends. A bright rim returns; the reddish hue fades. Alt ~72°, due S. Totality length ~82 minutes.
7. 1:26 am — Partial phase ends. Only the faint penumbral shading remains. Alt ~66°, SW.
8. 2:25 am — Penumbral ends. Eclipse over; normal full Moon brightness returns. Alt ~56°, WSW.

The entire event is comfortably visible from Mysore; no special equipment is needed, and it is safe to view with the naked eye (binoculars/telescopes just enrich the detail). 

Weather obliging, this eclipse should be easily observable by the vast majority of people in the country and elsewhere if they choose to do so.   There should be no cause for excuses. If you miss this, you will have to wait until December 31, 2028 for the next similar total lunar eclipse visible from Asia.  Remember, partial lunar (and even solar) eclipses are far from being as exciting as total ones, though more frequent.

[PS: At the time of uploading this post, the weather outlook in the southern part of Karnataka state, including the Mysore-Bangalore region, is not encouraging, but the probability of partial clear skies after sunset is high.]

Total lunar and solar eclipses

Total solar eclipses at any given location are extremely rare events, with a frequency of one in about 375 years. It is therefore no surprise that a place like Mysore has not seen one in living memory (An annular solar eclipse was visible on 26Dec19, but weather played spoilsport). In contrast, total lunar eclipses are far more frequent, typically a few times per decade. The disparity arises because a total lunar eclipse is visible from the entire hemisphere of Earth experiencing night, whereas a total solar eclipse is visible only over a very narrow path on Earth’s surface.

No eclipse of reason, please

Eclipses and such other natural phenomena have given rise to a vast storehouse of irrational beliefs, myths and superstitions in almost all civilizations all over the world.  No system of knowledge is immune from this.  Modern media are often guilty of fueling rather than fighting them.  In our society, people are strongly discouraged from even viewing these beautiful events live. Most of these beliefs are fanciful creations of the human mind, unsupported by tangible evidence that is consistent with the scientific method of inquiry.  Events like the forthcoming lunar eclipse should be viewed as opportunities not only to showcase some of the most amazing natural phenomena but also to demystify them from the myths and disbeliefs they are floundering in. The plain truth is that they are in no way connected with mundane human affairs. To argue otherwise would amount to an eclipse of reason!

Resource PACK

The Platform for Astronomy Communicators in Karnataka (PACK) is an informal platform for organizations and individuals (including this blogger) who engage in outreach and education in astronomy and related sciences, for students and general public, in English and Kannada, and promote science literacy and scientific temper.

This platform was formed on 12 July 2025 in the context of the need for coordination and planning for the Total Lunar Eclipse that is to occur on 7 September 2025. As an initiative of the Indian Institute of Astrophysics, Bangalore, it already has an impressive array of organizations and individuals as members taking active part in

• Coordination and networking, and sharing resource materials and information. 
• Encouraging in outreach and education in English, Kannada, and any other relevant languages for Karnataka.
• Offering open-source materials under a suitable Creative Commons license, and not allowing commercial use.

[If your organization or yourself would like to join the Platform, please email scope@iiap.res.in with some information about your work.]

The promotional materials of PACK (two of which are presented below for illustrative purposes) can be accessed at:

https://www.iiap.res.in/outreach/scope/projects/pack/ 

 

 

Disclaimer!

No special significance is intended in posting this article on my birthday!  Incidentally, the sum of the squares of the first four prime numbers gives (away) my age.  Back then, that day, so many years ago, nothing extraordinary is known to have happened in the ethereal heavens above or on terra firma below!

 

Appendix - Media focus

I have not been following reports of the impending eclipse closely enough in the media to offer any worthwhile comments.  However, they are unlikely to be significantly different from my observations (reproduced below) at the time of the event in 2011.  

Unlike total solar eclipses when the populist media goes into a frenzy with dark forebodings, the media glare during this eclipse was quite subdued and largely positive.  While the national level TV and print media gave generally accurate coverage both before and after the event, local media went about in their usual ways.  Astrologers and soothsayers had their usual say, with detailed prescriptions on how to protect oneself from or ward off the evil effects. 

Here are two samples of what was intended as some enlightened reporting: (i) The unusually long lunar eclipse, according to the astrologists, will have a negative effect on some zodiac signs, while it will benefit others; (ii) Natural calamities will affect the routine life of the countrymen, said astrologists when asked about the possible impact of this lunar eclipse on human lives.

I was interviewed by a Kannada TV channel on some technical aspects of the eclipse.  Among other things, the interviewer had pointedly asked me if there was any special type of radiation emitted during eclipses which would be harmful to people.  My responses in a two-minute video recording at home were whittled down to just twenty seconds in its actual news coverage of the day.  My obvious answer to the above question had been edited out.  To any viewer I must have appeared to be speaking irrelevantly.  This was followed by an equally short 'astrological evaluation' of the event by an appropriately attired astrologer who said something about the 'gravitational influence' of the event on people (no such influence exists), but otherwise mercifully refrained from predicting any grave consequences. 

A widely circulated Kannada newspaper gave equal space, side by side, to both the astronomical and astrological aspects of the impending eclipse.  I view this as a victory of sorts for science since the same newspaper had given three times as much space for the astrological aspects in its coverage of the great annular solar eclipse of 15 January last year (See my blog post titled: "Ring of Fire – The Great Annular Solar Eclipse of 15 Jan 10").  The astrological prescriptions this time included: (i) Performance of a 'Shanti' (penance) by people of just two 'rashis' who would be grossly affected by the eclipse (how considerate in excluding the vast majority of humans!), (ii) A much milder atonement by people of four other less severely affected 'rashis' by repeatedly chanting an exquisite sanskrit shloka invoking the mercy of the heavens during the eclipse (It didn't say how many times, but I believe the prevailing norm is one thousand), (iii) Abstaining from eating anything from as early as 12.30 afternoon on the 15th till the termination of the eclipse the following morning (One should welcome this strongly at least on health grounds), and (iv) Total exemption from fasting for children, the aged, the infirm and pregnant women (Again, how considerate, but how can one differentiate if birth dates and times are the sole criteria?).  In addition to these, there was of course the ever-implicit warning, very often explicit as well, that it would be harmful to view any eclipse in any manner anytime! 

 

 

Nobel Prizes

in

Astrophysics & Cosmology

(A 12-part series)

Part 2 – Energy of Stars: Hans A Bethe

 

Finally, I got to carbon, and as you all know, in the case of carbon the reaction works out beautifully. One goes through six reactions, and at the end one comes back to carbon. In the process one has made four hydrogen atoms into one of helium.

-       Hans Bethe

The Nobel Prize is equated with the pinnacle of human achievement in both popular perception and professional esteem.  Since it was first awarded in 1901, the annual Nobel Prize for Physics has gone to major contributions in Astrophysics and Cosmology related fields only on eleven occasions. The first of these awardees (1967) was the German-American Hans Albrecht Bethe for his discoveries concerning energy production in stars.

 

How energy is produced in stars

The mechanism of generation of energy in stars has been one of the long-lasting problems for scientists, with a clear-cut understanding emerging only relatively recently. Hans Bethe made a crucial contribution towards this end.

Here is a summary of how our understanding of stellar energy generation developed:

1. 19th Century – Gravitational Contraction Hypothesis

Hermann von Helmholtz (1850s) and Lord Kelvin proposed that stars shine by slowly contracting under gravity (the Kelvin–Helmholtz mechanism), converting gravitational potential energy into heat.  This could power the Sun for only about 20 million years — far too short for geological and biological evidence of Earth’s age.

2. Turn of the 20th Century – Role of Radioactivity

The discovery of radioactivity (Becquerel, Curie, Rutherford) raised the idea that nuclear processes might provide long-lasting energy, but details were unclear.

3. 1920 – Hydrogen-Fusion Idea

Arthur Eddington suggested that fusion of hydrogen into helium could release vast energy, explaining the Sun’s longevity. This was based on Einstein’s mass–energy equivalence and astrophysical reasoning, but lacked a known nuclear reaction pathway.

Arthur Eddington

4. 1930s – Quantum Tunnelling and Fusion Pathways

George Gamow introduced a factor for quantum tunnelling, explaining how nuclear fusion can occur at stellar temperatures despite the strong Coulomb repulsion between the hydrogen nuclei.

George Gamow

Hans Bethe and Carl von Weizsäcker independently worked out the main stellar fusion cycles:

Proton–Proton (pp) chain (dominant in Sun-like stars), and CNO cycle (dominant in hotter, massive stars). This became the modern nuclear theory of stellar energy.

Hans Bethe              Carl Von Weizsacker

5. Experimental Confirmation

Solar neutrinos detected (1960s, Ray Davis) confirmed nuclear fusion in the Sun, though initial results showed the “solar neutrino problem”. This was resolved in the early 2000s by ‘neutrino oscillation’ theory (concerning the way neutrinos change flavour as they travel).

6. Present Day – Precision Models

Stellar structure and evolution models now integrate nuclear physics, plasma physics, and particle physics to predict luminosities, lifetimes, and nucleosynthesis with high precision, validated by helioseismology and astrophysical observations.

More on stellar energy generation

Stars generate energy through nuclear fusion, a process that converts mass into energy according to Einstein's equation E=mc². This energy counteracts gravitational collapse, maintaining hydrostatic equilibrium. In the 19th century, gravitational contraction was considered the Sun's energy source, but calculations showed it could only power the Sun for 20-30 million years—far less than geological evidence suggested for Earth's age. Nuclear fusion resolved this discrepancy by offering a mechanism capable of sustaining stellar luminosity for billions of years.

Nuclear fusion requires temperatures large enough to overcome the Coulomb repulsion between atomic nuclei (millions of kelvin) and density that ensures sufficient particle collisions. He quantum tunnelling effect allows fusion below classical temperature thresholds (critical for lower-mass stars).

The proton-proton chain

The Primary Energy Source for Main-Sequence Stars is the Proton-Proton (PP) Chain which is dominant in stars ≤1.3 solar masses (e.g., the Sun) The process is depicted in the diagram below:

The energy yield is 26.2 MeV per helium-4 nucleus. (A 10% temperature increase boosts energy by 46%.)

The CNO Cycle (Carbon-Nitrogen-Oxygen)

This is dominant in stars >1.3 solar masses. The process is depicted in the diagram below:

The energy yield: 25.0 MeV per helium-4 nucleus, with greater neutrino losses. (A 10% temperature increase boosts energy by 350%.)

Hans Bethe's Seminal Contributions to Stellar Nucleosynthesis

In the 1930s, the source of stellar energy remained unresolved. Bethe, building on Arthur Eddington's hypothesis (1920) and George Gamow's quantum tunnelling work, sought a nuclear mechanism to explain stellar longevity.

Bethe published two papers in in 1939. The first paper detailed the proton-proton chain for low-mass stars, and the second one described the CNO cycle for high-mass stars, where carbon isotopes catalyse hydrogen fusion. Both processes convert hydrogen to helium, with 0.7% of fused mass released as energy.

Carl Friedrich von Weizsäcker had independently proposed the CNO cycle in 1938, but Bethe's work was more comprehensive. Initially, Bethe thought the CNO cycle powered the Sun due to overestimated core temperatures (20 MK vs actual 15.7 MK). Later experiments confirmed the PP dominance in the Sun.

Bethe was awarded the Nobel Prize in 1967 “for discoveries concerning energy production in stars", the first Nobel award specifically for an achievement in Astrophysics/Cosmology.

Bethe’s broader legacy

Bethe's work established stars as dynamic systems with "life cycles" (birth, evolution, death). The famous B2FH paper (1957), though not co-authored by Bethe, had a major influence on elemental synthesis. Bethe's models predicted neutrino fluxes, later confirmed by detectors like Homestake (Raymond Davis, 2002 Nobel prize) .

Detection of solar neutrinos (e.g., Super-Kamiokande experiments in Japan) confirmed hydrogen fusion in the Sun, and opened up the field of Neutrino Astronomy. Supernova remnants (e.g., Cassiopeia A) show enriched heavy elements, validating models of explosive nucleosynthesis. In galactic chemical evolution, stellar fusion products are recycled into molecular clouds, shaping the abundance of elements across cosmic time.

Bethe's work remains foundational, illustrating how quantum physics and nuclear theory solve cosmic puzzles. As he noted: "Stars have a life cycle much like animals... to give back the material of which they are made, so that new stars may live”. His insights continue guiding research in astrophysics, from stellar interiors to the origin of elements.

Hans A Bethe (1906-2005) – A biographical sketch

Early Life and Education

Hans Bethe was born on July 2, 1906, in Strasbourg, then part of the German Empire (now France). His father, Albrecht Bethe, was a physiologist, and his mother, Anna Kuhn, came from a family of academics. Growing up in an intellectually stimulating environment, Bethe displayed an early aptitude for mathematics and physics. 

After completing his secondary education in Frankfurt, he enrolled at the University of Frankfurt in 1924 but soon transferred to the University of Munich to study under the renowned physicist Arnold Sommerfeld.  Under Sommerfeld’s guidance, Bethe thrived in the rapidly evolving field of quantum mechanics. 

Doctoral Work and Early Career 

Bethe earned his PhD in 1928 with a thesis on electron diffraction in crystals, a foundational contribution to solid-state physics. He then conducted postdoctoral research at Cambridge (with Ralph Fowler) and Rome (with Enrico Fermi), deepening his expertise in quantum theory and nuclear physics. 

In the early 1930s, Bethe worked at the *University of Tübingen and later at Cornell University (from 1935), where he became a leading figure in theoretical physics. His work during this period included: 

• The Bethe formula (1930): Calculating the energy loss of charged particles passing through matter. 
• Nuclear physics (1936–1938): Developing theories of nuclear reactions and deuteron formation. 
• Quantum electrodynamics (QED): Later contributing to understanding the Lamb shift (1947). 

World War II and the Manhattan Project 

With the rise of the Nazis, Bethe, of Jewish descent, emigrated to the USA in 1935. During WWII, he joined the Manhattan Project (1942–1945) at Los Alamos, where J Robert Oppenheimer appointed him head of the Theoretical Division. There, his key contributions included critical mass calculations for nuclear weapons, the implosion mechanism for the plutonium bomb (tested at Trinity and used on Nagasaki). 

Though he supported the initial atomic bomb project, he later opposed the hydrogen bomb, advocating for arms control. 

After WWII, Bethe returned to Cornell University, where he continued groundbreaking work in multiple fields: 

1. Nuclear Physics: 

   - Bethe-Weizsäcker formula (1935) describing nuclear binding energies. 

   - Theory of nuclear reactions (1936–1939) explaining how stars produce energy (though astrophysics was a major focus, he also contributed to terrestrial nuclear processes). 

2. Solid-State Physics: 

   - Work on electron behaviour in metals and semiconductors. 

3. Quantum Field Theory:

   - Contributions to renormalization in QED alongside Feynman and Schwinger. 

The Nobel Award

The Nobel Prize in Physics 1967 was awarded to Hans Albrecht Bethe "for his contributions to the theory of nuclear reactions, especially his discoveries concerning the energy production in stars"

Hans A Bethe receiving his Nobel Prize in 1967

Interestingly, Bethe was not only the first recipient of the Nobel Physics Prize for work on Astrophysics, but also the sole one, unlike most awards in recent times.

Later Years and Public Advocacy

Bethe remained scientifically active well into his 90s, publishing papers on neutrino physics and supernovae. Beyond research, he was deeply engaged in science policy. He opposed the hydrogen bomb (1950s), signing the Einstein-Szilard letter warning of nuclear proliferation, advocated for the Partial Nuclear Test Ban Treaty (1963), and supported peaceful uses of nuclear energy, including fusion research. 

Personal Life and Outlook 

Bethe married Rose Ewald (daughter of physicist Paul Ewald) in 1939, and they had two children. Known for his modesty, warmth, and collaborative spirit, he mentored many future Nobel laureates, including Richard Feynman. 

Despite his role in developing the atomic bomb, Bethe believed in scientific responsibility, arguing that physicists must consider the ethical implications of their work. He remained optimistic about humanity’s ability to use science for good, once stating:  "The most important thing is to keep trying—to never stop asking questions." 

Death and Legacy

Hans Bethe died on March 6, 2005, in Ithaca, New York, at age 98. His legacy includes: the Bethe Prize, awarded for outstanding contributions to astrophysics.  His life’s work had a lasting influence across nuclear, quantum, and solid-state physics. 

Footnote

The picture below tells a story of its own. Bethe had visited Chennai (then Madras) apparently as a guest of the MatScience Institute or IITM.