A star normally appears steady against the night sky. But under very specific circumstances, it can suddenly vanish, return, disappear again, and then reappear several times within a matter of seconds or minutes. This unusual celestial event is called a grazing stellar occultation. It occurs when the apparent edge of a nearby astronomical body, most … Read more
An asteroid may be millions of kilometers away, appear as little more than a faint point of light, and still have its size measured surprisingly well from Earth. The trick is not necessarily to photograph the asteroid itself. Instead, astronomers can wait for the asteroid to pass directly in front of a distant star. For … Read more
A tiny asteroid millions of kilometers away may be far too small to appear as anything more than a faint point of light in a telescope. Sometimes it cannot be imaged clearly at all. Yet astronomers can still measure an asteroid only a few kilometers across, refine its position, estimate its shape, and occasionally discover … Read more
A pulsating white dwarf may look simple from the outside: a compact stellar remnant slowly cooling after exhausting its nuclear fuel. Inside, however, it is anything but uniform. Layers rich in hydrogen, helium, carbon, and oxygen can form sharp or gradual chemical boundaries. When gravity-mode pulsations travel through this layered interior, some waves interact strongly … Read more
A white dwarf may look almost featureless from the outside. It is small, faint, extremely dense, and no longer powered by ordinary nuclear fusion. Its visible atmosphere reveals useful information about temperature, surface gravity, and chemical composition, but much of the star’s history is locked far beneath that thin outer layer. Fortunately, some white dwarfs … Read more
A white dwarf may look like the quietest kind of star imaginable. It has exhausted its nuclear fuel. It no longer produces energy through sustained fusion in its core. It is roughly the size of Earth while containing a substantial fraction of the Sun’s mass, and over billions of years it simply cools and fades. … Read more
A white dwarf can look like the very definition of a quiet star. It is the compact remnant left behind after a Sun-like star has exhausted its nuclear fuel, shed its outer layers, and compressed its remaining core into an object roughly the size of Earth. There is no hydrogen fusion roaring in its center. … Read more
SU Ursae Majoris stars are small binary systems capable of surprisingly dramatic behavior. Most of the time, they are relatively faint. Every so often, however, their brightness suddenly increases in an ordinary dwarf-nova outburst. Then, after several such events, something larger happens: the system enters a superoutburst that lasts longer and usually reaches a greater … Read more
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