Astronomy explainers for curious readers: follow the evidence behind planets, distant small bodies, changing stars, and gravitational microlensing. Written from an enthusiast’s perspective, with attention to what observations can and cannot establish.
A stellar occultation can reveal a dwarf planet’s atmosphere by measuring how a background star fades as its light passes through the body’s limb. Gas can refract the light before the solid surface blocks it. The light curve constrains an atmosphere through a physical model; it is not a direct pressure gauge or a complete … Read more
A ring around a small Solar System body can be too faint and too close to its parent object to resolve in an ordinary image. A stellar occultation offers another route: use a distant star as a backlight and record what passes in front of it. The evidence comes from the timing and geometry of … Read more
A grazing stellar occultation happens when our line of sight to a star skims the apparent edge of a foreground body. In a lunar graze, mountains can hide the star while nearby valleys let it reappear. The resulting sequence of disappearances is a moving silhouette of lunar terrain, not a star switching on and off. … Read more
An asteroid occultation turns a brief disappearance of starlight into a measurement of an asteroid’s projected outline. The basic inputs are the disappearance and reappearance times, the observer’s location, and the shadow’s motion. The crucial qualification is that one observer normally measures a chord through the outline, not the asteroid’s full diameter. This guide follows … Read more
A tiny asteroid can be too faint to study in reflected sunlight yet still interrupt a much brighter background star. A stellar occultation uses that interruption to measure a silhouette. Its advantage is geometric: the asteroid need not be resolved into a disk. Its difficulty is temporal: the signal may last only a fraction of … Read more
Mode trapping is the unequal distribution of a pulsation’s motion within a layered star. In a pulsating white dwarf, composition transitions alter how buoyancy waves propagate. Some modes consequently sample an outer layer or a deeper region more strongly than neighboring modes do. “Trapped” does not mean a wave is sealed behind an impermeable wall. … Read more
White-dwarf asteroseismology infers internal structure by comparing observed pulsation periods with calculated stellar models. A telescope measures changing light, not a picture of the core. The result is therefore a constrained model of the interior, with uncertainties that depend on both the data and the physics used. Step 1: establish which frequencies belong to the … Read more
ZZ Ceti stars are white dwarfs with hydrogen-dominated atmospheres that exhibit nonradial pulsations. They are also called DAV variables: DA identifies the hydrogen-atmosphere spectral class, and V marks variability. Their changing light lets astronomers test models of compact stellar remnants. Classification requires more than a flickering light curve A white dwarf can vary because of … Read more
Many pulsating white dwarfs vary on minute-long timescales because they support gravity modes: standing oscillations restored by buoyancy inside a stratified star. Their changing surface temperature and emerging flux produce measurable brightness variations. The timescale is a property of a mode and the stellar structure, not simply the time a compact star takes to spin. … Read more
SU Ursae Majoris stars are interacting binaries that show ordinary dwarf-nova outbursts and longer superoutbursts. Gas transferred from a companion forms an accretion disk around a white dwarf. The leading thermal-tidal picture links a hot disk with an eccentric, precessing outer disk. The white dwarf does not need to explode. Separate the observation from the … Read more