Celestial mechanics is a branch of astronomy and physics that deals with the motions and gravitational interactions of celestial bodies, such as planets, moons, asteroids, comets, and stars. It involves the application of classical mechanics, particularly Newton's laws of motion and the law of universal gravitation, to understand and predict the behavior of these bodies in space.

Astroparticle physics is an interdisciplinary field of research that combines aspects of astrophysics and particle physics. It focuses on studying fundamental particles and the forces that govern them in the context of astronomical phenomena. The primary goal of astroparticle physics is to understand the universe at the intersection of the smallest scales (subatomic particles) and the largest scales (cosmic structures).

"Quantum chemistry stubs" likely refers to small, incomplete entries or frameworks related to quantum chemistry in a database, research repository, or knowledge base. The term "stub" is commonly used in collaborative platforms like Wikipedia or scientific databases to denote articles that are underdeveloped or in need of expansion. Such stubs often provide a basic introduction to a topic, outlining fundamental concepts, key figures, or relevant theories without going into comprehensive detail.

Wave mechanics is a branch of physics that deals with the study of waves and their behavior in various mediums. It forms an integral part of the broader field of quantum mechanics, particularly in the context of describing the behavior of particles at the quantum level. In wave mechanics, physical systems are described using wave functions, which encapsulate the properties of particles, such as their position and momentum.

Enumerative combinatorics is a branch of combinatorics concerned with the counting of structures that satisfy specific criteria. It involves the enumeration of combinatorial objects, such as permutations, combinations, graphs, and more, often under various constraints. The main goals of enumerative combinatorics include: 1. **Counting Objects**: Finding the number of ways to arrange or combine objects according to given rules. For example, how many ways can we arrange a set of books on a shelf?

Unsolved problems in astronomy encompass a wide range of questions and challenges that scientists and researchers are currently grappling with. Here are some of the major unsolved problems in the field: 1. **Dark Matter and Dark Energy**: While these components are believed to make up about 95% of the universe, their exact nature remains unknown. What is dark matter? Why does dark energy have a repulsive effect and drive the acceleration of the universe's expansion?

Spectroscopy is a scientific technique used to study the interaction of electromagnetic radiation with matter. It involves measuring the light spectrum emitted, absorbed, or scattered by materials in order to obtain information about their composition, structure, and physical properties. The basic principle of spectroscopy is that different substances interact with light in unique ways, producing distinct patterns or spectra that serve as "fingerprints" for identification and analysis.

Star formation is the process by which dense regions within molecular clouds in space collapse under their own gravity to form new stars. This process involves several stages and is a fundamental aspect of astrophysics and cosmology. Here are the key steps involved in star formation: 1. **Molecular Clouds**: Star formation begins in molecular clouds, which are large regions of gas and dust that are cool enough for hydrogen atoms to combine into molecules. These clouds are often referred to as stellar nurseries.