What Does it Mean – Part 2

Last week I made it into Messier of astronomy terminology and hopefully much of it made sense. Unfortunately, some terms or concepts do not lend themselves to descriptions that themselves are clear to everyone.


Ecliptic: I forgot this one last week. It’s the path among the stars our Sun takes in the sky. The Moon and planets also follow the ecliptic closely.

Meteor: It’s a streak of light, just the glow, light, smoke, explosion, etc., caused by a piece of solid material entering Earth’s atmosphere, going really fast (usually 20-40 miles per second). AKA – shooting star.

Meteor Shower: A bunch of meteors over a relatively short time interval. Usually due to Earth slamming into the trail of a comet’s particles along its orbit around our Sun.

Milky Way: What we earthlings named our home galaxy, just one of trillions.

Nebula: Latin, meaning “cloud”. Mostly composed of hydrogen gas and dust. Either bright, when lit up by stars, or dark when not lit up, and obscuring the view.

Occultation: Latin – To hide. Like an eclipse. When the Moon or planet passes directly in front of a more distant object and hides it.

Parallax: An object appears to be in different spots relative to its background when viewed from different places. Used to determine distances of faraway objects.

Phase: The fraction of an object illuminated by sunlight from our perspective.

Quasar: Some of the earliest forming galaxies, with supermassive black holes devouring gas and causing the galaxies to shine with incredible brilliance.

Reflector: A telescope that uses a mirror to gather light, often reflecting the light to another mirror that sends the light into an eyepiece or camera.

Refractor: A telescope that uses a lens to gather light, directing that light to an eyepiece or camera.

Retrograde: When a body appears to move reverse of its normal path. This happens with planets as Earth passes them in orbit.

Right Ascension (R.A.): Celestial equivalent to longitude.

Seeing: A measure of the atmosphere’s stability. More stability means better “seeing”.

Sidereal: Having to do with stars, their apparent movement and location.

Solstice: Summer (June 20), when the Sun is farthest north and winter (December 21) when its farthest south.

Terminator: Where the sunlit part meets the dark part of a planet or the Moon.

Transit: When a smaller object passes in front of a larger object without eclipsing it.

Transparency: A measure of the atmosphere’s clarity. Moisture and dust affect transparency.

Universal Time: AKA Greenwich Mean Time. It all begins at the Royal Observatory, Greenwich, London.

Waning: The changing (lessening illumination) of the Moon or other body after its full phase.

Waxing: The changing (increasing illumination) of the Moon or other body after its new phase.

Zenith: Directly overhead in the sky

Zodiac: Greek for “circle of animals”. The set of constellations located along the ecliptic in our sky.

What’s in the Sky?

July 26; before sunrise; east-northeast: A waning crescent Moon and Venus share the sky.

July 30; 1am and later; southeast: The Southern Delta Aquariid meteor shower peaks.