Methods include simply looking at the night sky with the naked eye, using binoculars, and using a variety of optical telescopes of varying power and quality, as well as additional sophisticated equipment, such as cameras, to study light from the sky in both the visual and non-visual parts of the spectrum.

Hand signals are used to assist the " eye in the sky ", a person or video camera located above the table and sometimes concealed behind one-way glass.

Comets visible to the naked eye are fairly infrequent, but comets that put on fine displays in amateur class telescopes ( 50 mm to 100 cm ) occur fairly often — as often as several times a year, occasionally with more than one in the sky at the same time.

Apart from the unusual Eta Carinae, Mira is the brightest periodic variable in the sky that is not visible to the naked eye for part of its cycle.

It was not until the Han Dynasty ( 202 BC-220 AD ) that astronomers started to observe and record names for all the stars that were apparent ( to the naked eye ) in the night sky, not just those around the ecliptic.

Visible to the naked eye, Kepler's Star was brighter at its peak than any other star in the night sky, and all the planets ( other than Venus ), with apparent magnitude − 2. 5.

It became said that the sun was his right eye and the moon his left, and that they traversed the sky when he, a falcon, flew across it.

One of Horus ' major roles is as a sky deity, and for this reason his right eye was said to be the sun and his left eye the moon.

The diffuse aurora is a featureless glow in the sky which may not be visible to the naked eye even on a dark night and defines the extent of the auroral zone.

It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky.

Initially, in that system, the Moon had been seen to be the eye of Horus, the sky god, which had been semi-blinded ( thus darker ) in a fight against Set, the other eye being the Sun.

It is more difficult to find the south celestial pole in the sky at this moment, as that area is a particularly bland portion of the sky, and the nominal south pole star is Sigma Octantis, which with magnitude 5. 5 is barely visible to the naked eye even under ideal conditions.

The hieroglyph for her eye is shown below ; sometimes two are shown in the sky of religious images.

While re-observing his first comet ( which never became visible to the naked eye ) and the surrounding patch of sky, Hyakutake was surprised to find another comet in almost the same position as the first had been.

Hugo's poem concerns a man haunted by an eye that stares at him unceasingly from the sky.

Known as Unmanned Aerial Vehicles, these drones are a force multiplier by giving the battlefield commander an " eye in the sky " without risking a pilot.

They were initially called novae, from the Latin ' new ', since ones with an outburst brightness visible to the naked eye and a quiescent brightness invisible appeared as new stars in the sky.

It is one of the brightest nebulae, and is visible to the naked eye in the night sky.

Picture of the sky in the eye of a tropical cyclone

The result is that the human eye perceives blue when looking toward parts of the sky other than the sun.

Whatever his original assignment, the fictional private eye ends up by investigating and solving a crime, usually a murder.

For one thing, the driver usually sees less and has less fun than his passengers since it becomes pretty necessary for him to keep at least one eye on the road.

In mammals it is usually referred to as the superior colliculus, and its best-studied function is to direct eye movements.

Though the Shang did not have a concept of " medicine " as distinct from other fields, their oracular inscriptions on bones and tortoise shells refer to illnesses that affected the Shang royal family: eye disorders, toothaches, bloated abdomen, etc., which Shang elites usually attributed to curses sent by their ancestors.

Tapestry cartoons, usually coloured, were followed by eye by the weavers on the loom.

On the Nature of Animals, (" On the Characteristics of Animals " is an alternative title ; usually cited, though, by its Latin title ), is a curious collection, in 17 books, of brief stories of natural history, sometimes selected with an eye to conveying allegorical moral lessons, sometimes because they are just so astonishing:

London Dry gin is usually distilled in the presence of accenting citrus elements, such as lemon and bitter orange peel, as well as a subtle combination of other spices, including any of anise, angelica root and seed, orris root, licorice root, cinnamon, almond, cubeb, savory, lime peel, grapefruit peel, dragon eye, saffron, baobab, frankincense, coriander, grains of paradise, nutmeg and cassia bark.

The whale feeds mainly on benthic crustaceans, which it eats by turning on its side ( usually the right, resulting in loss of eyesight in the right eye for many older animals ) and scooping up sediments from the sea floor.

Due to a protruding left eye, Keller was usually photographed in profile.

At this point, the infusoria will be ready, and will usually be visible to the naked eye as small, white specks swimming in the container.

Because of this, these devices are usually operated between crossed polarizers such that they appear bright with no voltage ( the eye is much more sensitive to variations in the dark state than the bright state ).

The maintaining of eye contact is usually the first sign of aggression, while laid-back ears or a lowered head is a definite sign of agitation.

Highcolor, usually meaning 16 bpp, normally has five bits for red and blue, and six bits for green, as the human eye is more sensitive to errors in green than in the other two primary colors.

Their eye color is usually dark-brown.

This tube is usually almost level with the eye sockets but when this sometimes hereditary abnormality is present, it is below this level and sometimes level with the vestibule or nasal entrance.

Owls have large forward-facing eyes and ear-holes ; a hawk-like beak ; a flat face ; and usually a conspicuous circle of feathers, a facial disc, around each eye.

Because the U. S. Bureau of the Mint keeps a careful eye on all potential errors, errors on U. S. coins are very few and usually very scarce.

The infection usually begins with one eye, but may spread easily to the other.

Viral conjunctivitis, commonly known as pink eye, shows a fine, diffuse pinkness of the conjunctiva, which is easily mistaken for the ciliary injection of iritis, but there are usually corroborative signs on microscopy, particularly numerous lymphoid follicles on the tarsal conjunctiva, and sometimes a punctate keratitis.

Like viral conjunctivitis, it usually affects only one eye but may spread easily to the other eye.

The upper jaw ( maxilla ) extends to the back of the eye, which is usually red.

Individual zooplankton are usually too small to be seen with the naked eye, but some, such as jellyfish, are large.

However, some nouns are pronounced differently in their plural forms: for example, œil (" eye ") becomes yeux, cheval (" horse ") becomes chevaux, and os (" bone " or " bones ") is pronounced differently when it is plural () from when it is singular (); and even with nouns for which this is not the case, a distinction will still usually be made in speech, as there will usually be a neighboring article or determiner whose pronunciation does change with the noun's number ( due to number agreement ; see below ).