see¹ / sē/ • v. (sees / sēz/ , see·ing / sē-ing/ ; past saw / sô/ ; past part. seen / sēn/ ) [tr.] 1. perceive with the eyes; discern visually: in the distance she could see the blue sea | [intr.] Andrew couldn't see out of his left eye | fig. I can't see into the future. ∎  be or become aware of something from observation or from a written or other visual source: I see from your appraisal report that you have asked for training. ∎  be a spectator of (a film, game, or other entertainment); watch: I went to see King Lear at the Old Vic. ∎  visit (a place) for the first time: see Alaska in style. ∎  [in imper.] refer to (a specified source) for further information (used as a direction in a text): elements are usually classified as metals or nonmetals (see chapter 11). ∎  experience or witness (an event or situation): I shall not live to see it | [tr.] I can't bear to see you so unhappy. ∎  be the time or setting of (something): the 1970s saw the beginning of a technological revolution. ∎  observe without being able to affect: they see their rights being taken away. ∎  (see something in) find good or attractive qualities in (someone): I don't know what I see in you.2. discern or deduce mentally after reflection or from information; understand: I can't see any other way to treat it | I saw that perhaps he was right she could see what Rhoda meant. ∎  ascertain after inquiring, considering, or discovering an outcome: I'll go along to the club and see if I can get a game. ∎  [tr.] regard in a specified way: he saw himself as a good teacher you and I see things differently. ∎  foresee; view or predict as a possibility: I can't see him earning any more anywhere else. ∎  used to ascertain or express comprehension, agreement, or continued attention, or to emphasize that an earlier prediction was correct: it has to be the answer, don't you see? see, I told you I'd come.3. meet (someone one knows) socially or by chance: I went to see Caroline I saw Colin last night. ∎  meet regularly as a boyfriend or girlfriend: some guy she was seeing was messing her around. ∎  consult (a specialist or professional): you may need to see a solicitor. ∎  give an interview or consultation to (someone): the doctor will see you now.4. [tr.] escort or conduct (someone) to a specified place: don't bother seeing me out. ∎  [intr.] (see to) attend to; provide for the wants of: I'll see to Dad's tea. ∎  [intr.] ensure: Lucy saw to it that everyone got enough to eat and drink | see that no harm comes to him. 5. (in poker or brag) equal the bet of (an opponent).PHRASES: as far as I can see to the best of my understanding or belief.as I see it in my opinion.be seeing thingssee thing. (I'll) be seeing youanother way of saying see you.have seen better days have declined from former prosperity or good condition: this part of South London has seen better days.have seen it all before be very worldly or very familiar with a particular situation.let me see said as an appeal for time to think before speaking: Let me see, how old is he now?see a man about a dog humorous said euphemistically when leaving to go to the toilet or keep an undisclosed appointment.see eye to eye,see fit, etc. see eye, fit¹ , etc.see here! said to give emphasis to a statement or command or to express a protest: now see here, you're going to get it back for me!see one's way clear to do (or doing) something find that it is possible or convenient to do something (often used in polite requests).see someone coming recognize a person who can be fooled or deceived.see something coming foresee or be prepared for an event, typically an unpleasant one.see someone right Brit., inf. make sure that a person is appropriately rewarded or looked after.see sense (or reason) realize that one is wrong and start acting sensibly.see the back of Brit., inf. be rid of (an unwanted person or thing): we were always glad to see the back of her.see you (later) inf. said when parting from someone.we'll see about that said when angrily contradicting or challenging a claim or assertion: Oh, you think it's funny, do you? We'll see about that!PHRASAL VERBS: see about attend to; deal with: he had gone to see about a job he had heard of.see after take care of; look after.see something of spend a specified amount of time with (someone) socially: we saw a lot of the Bakers. ∎  spend some time in (a place): I want to see something of those countries.see someone off accompany a person who is leaving to their point of departure: they came to the station to see him off.see through not be deceived by; detect the true nature of: he can see through her lies and deceptions.see someone through support a person for the duration of a difficult time.see something through persist with an undertaking until it is completed.DERIVATIVES: see·a·ble adj.see² • n. the place in which a cathedral church stands, identified as the seat of authority of a bishop or archbishop.

Seeing

Astronomical seeing refers to the ability to view celestial objects through the obscurations of the earth's atmosphere. These obscurations include opacity, scattering, turbulence, atmospheric and thermal emission, and ionization.

Opacity refers to the fact that Earth's atmosphere is transparent only to relatively narrow wavelength ranges of light. These include visual light, the near infrared, microwaves and radio waves with wavelengths between about 0.35 mm and 1 m. The atmosphere is almost completely opaque to ultraviolet light, x rays, gamma rays, and radio waves with wavelengths greater than 1 m. The need to observe heavenly bodies outside of these narrow wavelength windows, along with the desirability to avoid the degrading affects of the atmosphere are among the main reasons for the development of space-based telescopes.

Ultraviolet photons are absorbed by electron transitions in oxygen and ozone atoms in the upper atmosphere. Because the amount of ozone varies greatly with location and seasonal time of year (e.g., the hole in the ozone layer over Antarctica during the winter) so does the amount of ultraviolet light reaching the surface of Earth. Ultraviolet light is mainly absorbed by molecular nitrogen. Infrared light is absorbed mainly by water vapor and carbon dioxide in the earth's atmosphere. Millimeter wavelengths are absorbed by rotational bands of water and molecular oxygen, while long radio waves are absorbed by ions high in the earth's atmosphere. Because 50% of the water vapor lies within three kilometers of the earth's surface, to some degree the infrared spectrum may be observed with instruments located on high mountains, or mounted on airplanes or balloons. Wavelength regions at which the atmosphere is transparent are called atmospheric windows.

Scattering of light particles degrades seeing. The mechanism by which molecules scatter visible light is called Rayleigh scattering, and the degree to which light is scattered is inversely proportional to the fourth power of the wavelength and proportional to the density of atmosphere. Thus, blue light is scattered more strongly than red light, accounting for the blue color of the sky. Red sunsets are an optical illusion caused by the intense scattering of blue light as the light rays travel through the horizon-level thickest regions of the atmosphere.

Atmospheric turbulence resulting from thermal currents, or wind , creates small changes in the density of pockets of air that cause the direction of light rays from point sources such as stars to be changed by refraction. In effect, the position of the star seems to shift slightly, and the star appears to twinkle. On a photographic plate, turbulence results in a smearing of the stellar image. Details of planetary features are often highly obscured and degraded by turbulence. The human eye, which processes light almost instantly, often sees a much sharper image than may be obtained with photographs.

Atmospheric emission of the night sky, also called air-glow, is caused by the recombination of electrons with atoms that were ionized during the day by photochemical dissociation. This fluorescent light arises from neutral oxygen atoms and molecules, sodium, hydrogen, and hydroxide molecules, and is emitted about 100 km above the earth's surface. The total airglow over one arcsecond, roughly the apparent size of a star with a large telescope , corresponds to a visual magnitude of 22. Thus, stars dimmer than this, or galaxies with a surface area brightness less than this, are difficult to detect.

Thermal emission of the night sky is also a factor in the near infrared part of the spectrum. Any warm object in thermal equilibrium will emit black body radiation (e.g., iron heated to several hundred degrees will glow red or white). The earth's atmosphere below about 50 km emits a faint light by this mechanism, equivalent to a few Janskys (10⁻²⁶ Watts/m²Hz).

Ionization in the earth's ionosphere degrades radio waves. Turbulence in this layer of the atmosphere causes small fluctuations in the density of free electrons, which alter the direction of radio waves and cause dispersion in the frequencies of the radio waves. A radio wave emitted from a star of a particular wavelength or frequency will be dispersed into a small range of frequencies by ionization.

See also Astronomy; Atmospheric chemistry; Atmospheric circulation; Atmospheric composition and structure; Atmospheric inversion layers; Atmospheric pollution; Space and planetary geology

see·ing / ˈsē-ing/ • conj. because; since: seeing as Stuart's an old friend, I thought I might help him out.• n. the action of seeing someone or something. ∎  Astron. the quality of observed images as determined by atmospheric conditions.

see1 pt. saw, pp. seen perceive with the eyes. OE. str. vb. sēon = OS., OHG. sehan (Du. zien, G. sehen), ON. sjá, Goth. saihwan :- Gmc. *seχwan — IE. *seq-, by some identified with the base of L. sequī follow, the etym. sense being ‘follow with the eyes’.

see the place in which a cathedral church stands, identified as the seat of authority of a bishop or archbishop. The word comes (in Middle English, via Anglo-Norman French) from Latin sedes ‘seat’.