Sky event guide Sky Events
Sky events
Most of what happens on schedule overhead can be known in advance.
Meteor showers, conjunctions, oppositions, elongations, lunar phases and eclipses: what causes each recurring sky event, how often it returns, and how to watch it.
- Events covered
- 20
- Categories
- 5
- Equipment needed
- Naked eye
01 / Meteor showers
Meteor showers
A meteor shower is dust a comet or asteroid left strewn along its orbit. Earth crosses the same stream on nearly the same dates every year, and the grains enter the atmosphere at tens of kilometres per second, glowing as they vaporise some 80 to 120 km up. Because their paths are parallel, perspective makes every meteor appear to radiate from one point on the sky — which is why showers are named after the constellation holding that radiant.
QuadrantidsQuadrantids
Early January, every year
A winter shower whose peak lasts only a few hours, from what may be a dormant comet.
LyridsLyrids
Late April, every year
A spring shower recorded for more than two thousand years, with occasional brief outbursts.
Eta AquariidsEta Aquariids
Early May, every year
Fast meteors from Halley’s dust, far better placed for the southern hemisphere.
PerseidsPerseids
Mid-August, every year
The best-placed annual shower for the north: steady rates, and warm nights at maximum.
OrionidsOrionids
Late October, every year
Halley’s dust again: near-maximum speed, with a broad and forgiving peak.
LeonidsLeonids
Mid-November, every year
Quiet in most years, yet capable of a storm around its parent comet’s return.
GeminidsGeminids
Mid-December, every year
The year’s richest shower, and the one whose parent is an asteroid.
UrsidsUrsids
Late December, every year
A modest shower right after the Geminids, with a radiant that never sets.
02 / Planetary aspects
Planetary aspects
When a planet is visible, how bright it looks, and which part of its lit side faces us all follow from where it, Earth and the Sun stand relative to one another. Conjunction, opposition, greatest elongation, transit and occultation each name one special moment in that geometry.
ConjunctionConjunction
Irregularly, all year round
Two bodies draw almost together on the sky while remaining vastly far apart.
OppositionOpposition
Once every one or two years for an outer planet
Planet and Sun stand on opposite sides of Earth: visible all night, and at its brightest.
Greatest elongationGreatest elongation
Several times a year for Mercury, about every 19 months for Venus
An inner planet reaches its greatest angle from the Sun, and its easiest visibility.
TransitTransit
About 13 Mercury transits per century
An inner planet crosses the solar disc: rare, and only ever watched through a proper filter.
OccultationOccultation
Lunar occultations happen every month
A nearer body passes in front of a more distant one and briefly hides it.
03 / The Moon
The Moon
The phases are a direct read-out of where the Sun, Earth and Moon stand; Earth’s shadow plays no part in them. Over one synodic month we simply see different fractions of the Moon’s sunlit half — and because its orbit is not a circle, the changing distance also changes how large and bright a full Moon appears.
Lunar phasesLunar phases
A cycle of about 29.5 days
The angle at which the Moon’s sunlit half faces Earth changes, and a month of phases follows.
SupermoonSupermoon
Three or four times a year
A full Moon that falls near perigee, and so looks larger and brighter.
Blue moonBlue moon
Once every two or three years
A calendar coincidence with nothing to do with colour: one full Moon more than usual.
04 / Eclipses
Eclipses
When the Sun, Earth and Moon line up closely enough, one body’s shadow falls on another. The Moon’s orbit is tilted about 5° to the ecliptic, so eclipses happen only near the nodes — which is exactly why the observatory’s sky-event planner can list future solar and lunar eclipses one after another.
05 / Sun and Earth
Sun and Earth
Earth’s own motion produces recurring events too: the tilt of its axis sets how day length and noon Sun altitude change through the year, while its elliptical orbit makes the distance to the Sun rise and fall. The two are often confused, yet one governs the seasons and the other only the apparent size of the solar disc.
Equinoxes and solsticesEquinoxes and solstices
Four times a year
Four turning points set by Earth’s tilt, governing day length and the seasons.
Perihelion and aphelionPerihelion and aphelion
Once each per year
Earth’s orbit is not a circle: the distance to the Sun varies by about five million kilometres.