Most dwarf novae are creatures of rhythm. They brighten dramatically, fade back into quiescence, wait while their accretion disks refill, and then repeat the cycle. Z Camelopardalis stars, better known as Z Cam stars, occasionally break that rhythm. Instead of fading normally after an outburst, a Z Cam system may become stuck at an intermediate … Read more

A dwarf nova can spend days, weeks, or even months looking remarkably quiet. Then, sometimes in less than a day, its brightness surges. To an observer, the change can seem almost explosive. A faint cataclysmic variable suddenly becomes several magnitudes brighter, remains conspicuous for a few days, and then fades back toward quiescence. The name … Read more

Cataclysmic variable stars are binary systems in which a white dwarf pulls material from a nearby companion star. Because mass is continually transferred between the two stars, these systems are laboratories for studying accretion, stellar evolution, magnetic fields, and orbital dynamics. One of their most curious features is something that is not seen very often … Read more

A dwarf nova can brighten dramatically during an outburst, but for astronomers studying SU UMa-type systems, the overall rise and fall in brightness is only part of the story. Hidden inside the light curve is a much faster repeating signal known as a superhump. A superhump may repeat every hour or two. Its period can … Read more

Cataclysmic variable stars are among the most restless binary systems in the sky. Their brightness can change dramatically as matter flows from one star to another, accretion disks flare, and occasionally a white dwarf undergoes a nova eruption. But astronomers are interested in more than brightness. One of the most revealing quantities in a cataclysmic … Read more

A contact binary star system may look remarkably stable at first glance. Two stars orbit one another again and again, often completing an entire orbit in less than a day. Their eclipses can repeat so regularly that astronomers can predict them thousands of cycles into the future. But when eclipse timings are measured carefully over … Read more

Binary stars can behave like some of the most precise clocks in the sky. When two stars orbit one another and their orbital plane happens to be aligned with our line of sight, one star periodically passes in front of the other. The resulting decrease in brightness creates an eclipsing binary. At first glance, astronomers … Read more

If a variable star is supposed to reach maximum brightness at 10:00 p.m. but actually reaches it at 10:07 p.m., those seven minutes are not necessarily just an observational nuisance. Repeated over months, years, or decades, such timing differences can reveal that the star’s period is changing. An O-C diagram, pronounced “O minus C,” is … Read more

When an exoplanet passes in front of its star, astronomers can measure a tiny decrease in the star’s brightness. This seemingly simple dip in light is one of the most powerful tools in modern astronomy. From it, researchers can estimate a planet’s size, orbital period, and sometimes even study gases in its atmosphere. But there … Read more

An exoplanet transit looks deceptively simple. A planet passes in front of its host star, blocks a small fraction of the starlight, and produces a dip in the observed light curve. If the same planet crosses the same star again, it might seem reasonable to expect exactly the same dip every time. Yet astronomers sometimes … Read more