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Stars are mostly found in binary and multiple systems, as at least 50% of all solar-like stars have companions - a fraction that goes up to 100% for the most massive stars. Moreover, a large fraction of them will interact in some way or…
The indigenous astronomy in Africa and of Africans exhibits many of the same patterns as indigenous astronomy found in other parts of the world such as with agricultural calendars established by observing celestial bodies as well as other…
Planetary systems appear to form contemporaneously around young stars within young star-forming regions. Within these environments, the chances of survival, as well as the long-term evolution of these systems, are influenced by factors such…
(shortened) Direct N-body calculations are presented of the formation of Galactic clusters using GasEx, which is a variant of the code Nbody6. The calculations focus on the possible evolution of the Orion Nebula Cluster (ONC) by assuming…
In spite of much work, the overall spiral structure morphology of the Milky Way remains somewhat uncertain. In the last two decades, accurate distance measurements have provided us with an opportunity to solve this issue. Using the precise…
Stellar multiplicity is among the oldest and richest problems in astrophysics. Binary stars are a cornerstone of stellar mass and radius measurements that underpin modern stellar evolutionary models. Binaries are the progenitors of many of…
Launched more than thirty years ago and now drifting in space with no further contact, the Pioneer 10 and 11 spacecraft are currently at the center of a small but developing concern: are they under the influence of an anomalous acceleration…
A primeval galaxy represents the earliest stages of a galaxy's life and as such provides clues to the early history of the Universe and the evolution of stars and galaxies. Over the last 20 years astronomers have been engaged in the quest…
In this experimental work we study billiard trajectories in triangular pyramids and try to establish conditions that guarantee the existence (or absence) of 4-cycles (there can be not more, than three of them). We formulate conjectures and…
M-dwarf stars are more abundant than G-dwarf stars, so our position as observers on a planet orbiting a G-dwarf raises questions about the suitability of other stellar types for supporting life. If we consider ourselves as typical, in the…
We present HST observations that show a bifurcation of colors in the middle main sequence of the globular cluster Omega Centauri. We see this in three different fields, observed with different cameras and filters. We also present high…
Microlensing surveys suggest the presence of a surprisingly large population of free-floating planets, with a rate of about two Neptunes per star. The origin of such objects is not known, neither do we know if they are truly unbound or are…
An asteroid pair can be described as two asteroids with highly similar heliocentric orbits that are genetically related but not gravitationally bound. They can be produced by asteroid collisions or rotational fission. Although over 200…
Stars are generally spherical, yet their gaseous envelopes often appear non-spherical when ejected near the end of their lives. This quirk is most notable during the planetary nebula phase when these envelopes become ionized. Interactions…
The ease of interstellar rocket travel is an issue with implications for the long term fate of our own and other civilizations and for the much-debated number of technological civilizations in the Galaxy. We show that the physical barrier…
Every society has a story rooted in its most ancient traditions, of how the earth and sky originated. Most of these stories attribute the origin of all things to a Creator - whether God, Element or Idea. We first recall that in the Western…
Stars formed in clusters can encounter other stars at close distances. In typical open clusters in the Solar neighbourhood containing hundreds or thousands of member stars, ten to twenty per cent of Solar-mass member stars are expected to…
Their ubiquity and extreme densities make star clusters probes of prime importance of galaxy evolution. Old globular clusters keep imprints of the physical conditions of their assembly in the early Universe, and younger stellar objects,…
As we discover numerous habitable planets around other stars in the Milky Way galaxy, including the nearest star, Proxima Centauri, one cannot help but wonder why have we not detected evidence for an advanced alien civilization as of yet.…
A specially interesting subgroup of asteroid families are young ones, i.e. those formed less than 10 Myrs ago. They have attracted a lot of attention since the first such family has been discovered in 2002. About 20 young families have been…