Lyman Spitzer was one of the major figures of twentieth centurytheoretical astrophysics. Over more than fifty years,he kept up sustained research of his own, on problems concerningthe interstellar medium, star formation, and galaxies.In addition he was a major influence on observationalprogrammes, and created a thriving school of theoretical astrophysicsat Princeton University along with a strong plasmaphysics programme. This article brings out his contributions,placing them in context.

The interstellar gas in galaxies is heated by stellar radiationand cosmic rays and it also cools through radiation. We takea detailed look at these processes in order to understand thethermal state of equilibrium of the interstellar gas. This gasalso manifests itself in different ‘phases’– molecular, neutralatomic and ionized, each with its characteristic temperatureand density, which we attempt to understand.

Freshwater ecosystems and associated habitats harbor incrediblebiodiversity. They offer various ecosystem services andsustain human livelihoods. However, due to increasing developmentalpressure and rising water demand, these systemsare under huge threat. As a result, many aquatic species arefeared to become extinct in near future. Quantifying the patternsof aquatic species diversity and composition of river systemsis urgently required. With this interest, we studied fourriver systems in the Western Ghats region, documenting thepattern of fish diversity and identifying the factors that influencefish species richness. Maintaining undisturbed streamsand river basins, especially headwater regions is crucial forsustaining freshwater biodiversity in the tropical river ecosystems.

After the pollen grain reaches the stigma through outsourcedagents (pollinators), the next step before fertilization is to selectthe right type of pollen. Similar to a marriage in humanbeings, flowering plants also have evolved elaborate screeningprocess to select the right pollen grains and to reject thewrong ones. Even after initial screening for the right pollen,the pistil imposes a tough competition amongst them, comparableto a swayamvara of Indian mythology, to select the bestavailable pollen. Flowering plants have evolved into a matriarchalsociety. The selection of the male partner is totally theprerogative of the mother (pistil); the boy (pollen grain) andthe girl (ovule) has no say in this selection.

This article contains very simple mathematics and a lot ofcreativity. Here, we will sketch a 3-dimensional flower-likestructure, not using complicated equations but geometric ideasinstead. The speciality of 1235711 will be mentioned. At firstwe will study a general situation in 3-dimensional space $\mathbb{R}^{3}$ and then we will take up the flower as an example of the generalcase.

In this article we shall mathematically analyse the Resistor-Capacitor (RC) circuit with the help of Fourier transforms(FT). This very general technique gives us a lot of insight intosolving first order differential equations with source terms dependingon time. In itself, the RC circuit is by far the mostcommonplace entity in modern electronics. But the method ofFT is not the accepted custom for an electronic engineer, whois probably more comfortable working with complex impedancesand phasors while solving problems in network analysis.In fact, what is used much more extensively is the Laplacetransform. But a lot of things, (including the complex impedanceitself, and some insight into complex analysis) can be understoodbetter if we use the FT approach to solve the differentialequations that come up in network analysis. The use of FTcomes smoothly from first principles – precisely what we setout to demonstrate here.