Constellations and asterisms are patterns of stars. Some asterisms consist of stars from different constellations, and some are part of one constellation.
Black holes are regions of space with gravitational fields so strong that nothing, not even light, can escape. Their sizes vary from stellar to supermassive.
What are red giants? Most main-sequence stars, like our sun, will become one. Red giants swell to such a large size they can swallow their inner planets.
What is a variable star? It's a star that brightens and dim in a cycle that might last hours, or weeks, or months, or longer. Astronomers know millions!
A quasar is an extremely bright, distant object visible to radio telescopes. The source is an active galactic nucleus fueled by a supermassive black hole.
Andy Briggs has spent the past 30 years communicating astronomy, astrophysics and information technology to people. You can hear his weekly astronomy and space news update, on Mondays, on the global internet radio channel AstroRadio (http://www.astroradio.earth), where he also contributes to other programmes. He has been active in many astronomy societies in the UK and is a frequent contributor to Astronomy Ireland magazine. Andy also lectures regularly on astrophysics-related themes such as gravitational waves and black holes. He lives in Catalonia, Spain, with his daughter.