In Astronomy, the expression celestial event refers an astronomical event involving one or more celestial objects and which can be seen by earth bound observers either during the day or at night. Further, celestial events are often visible with the naked eye while some require the aid of binoculars or a telescope. This expression is primarily used when referring to predictable viewable phenomenon such as comets, conjunctions, equinoxes, lunar eclipses, meteor showers, moon phases, occultations, planetary oppositions, solar eclipses, solstices and transits.

The term astronomical event often means the same thing as celestial event, but a celestial event suggest a phenomenon which is observable in the sky by earth bound viewers and from within the celestial sphere, whereas, an astronomical event may also be meant to include other events in the realm of astronomy that occur in the universe but are not necessarily visible from earth bound observers.

Thus, astronomical events would include those not necessarily observable to earth bound viewers such as: blazars, cosmic microwave background radiation, gamma ray bursts, pulsars, quasars and supernova explosions.

The study of astronomy has been the basis of man′s ability to discover and then predict celestial phenomena. Astronomy applies mathematics, physics, and chemistry in an effort to explain and understand objects of interest and to predict the celestial phenomena that abound in the heavens. The objects of interest include asteroids, comets, galaxies, moons, nebula, planets, and stars. The phenomena includes both those that are known as celestial event as well as those that are astronomical events.

All of the phenomena that originate outside Earth′s atmosphere are within the undertaking of the study of astronomy. A related but distinctly different subject is physical cosmology, which is the study of the Universe as a whole.

Astronomy is a natural science and is one of if not the oldest of this type of science. Most all early civilizations and most indigenous people performed methodical observations of the night sky. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars, but professional astronomy now is considered synonymous with astrophysics, and split into observational and theoretical branches.

Historically, the longest ever total eclipse lasted 7 minutes, 27.54 seconds on 15 June 743 BCE. Theoretically, the longest eclipse possible is 7 minutes, 32 seconds.

Nevertheless, the distance of Apophis from the Earths will be less than 22,000 miles (35,000 km), which in astronomical distances, is extremely close for the physical distance between two celestial objects.

Furthermore, the Leonids are known for their spectacular meteor storm every 33 years which produces some 1000 meteors per hour. However, the very best years of this Leonid 33 year cycle will occur in 2034/2035. During that period of the Leonids, the materials left from the comet should amount to up to 1600 Leonid meteors per hour, followed some hours later by another surge of activity from material shed by its return in 1767, which material would amount to about 1000 Leonid meteors per hour.

When we talk about planetary alignment, it does not suggest that the planets line up in a perfectly straight line in space. Rather, we are usually referring to a celestial event wherein multiple planets appear from an Earthbound perspective to be aligned together in the night sky. This phenomenon can also be a type of conjunction.