# octant

## Definitions

• WordNet 3.6
• n octant a measuring instrument for measuring angles to a celestial body; similar to a sextant but with 45 degree calibration
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Webster's Revised Unabridged Dictionary
• Octant An instrument for measuring angles (generally called a quadrant), having an arc which measures up to 9O°, but being itself the eighth part of a circle. Cf. Sextant.
• Octant (Math. & Crystallog) One of the eight parts into which a space is divided by three coördinate planes.
• Octant (Geom) The eighth part of a circle; an arc of 45 degrees.
• Octant (Astron. & Astrol) The position or aspect of a heavenly body, as the moon or a planet, when half way between conjunction, or opposition, and quadrature, or distant from another body 45 degrees.
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Century Dictionary and Cyclopedia
• n octant The eighth part of a circle.
• n octant In astronomy, that position or aspect of two heavenly bodies, especially a planet and the sun, when half-way between conjunction or opposition and quadrature, or distant from one another by the eighth part of a circle, or 45°. The moon is said to be in her octants when she is half-way between new or full moon and one of her quarters. The octants of the moon are especially important, because the third inequality or variation, which comes to its maximum in those positions, is considerable. Also octile.
• n octant An instrument used by seamen for measuring angles, resembling a sextant or quadrant in principle, but having an arc the eighth part of a circle, or 45°. By double reflection it can measure an arc of 90°. See sextant. Hadley's quadrant is really an octant.
• n octant Each of the eight regions into which space is divided by three copunctal non-costraight planes.
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Chambers's Twentieth Century Dictionary
• n Octant ok′tant the eighth part of a circle: an instrument for measuring angles: the aspect of two planets when 45°, or one-eighth of a circle, apart
• Octant Also Oc′tile
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## Etymology

Webster's Revised Unabridged Dictionary
L. octans, -antis,. fr. octo, eight. See Octave

## Usage

### In literature:

Error of Octant 2 deg.
"The Journals of Lewis and Clark" by Meriwether Lewis and William Clark
The flat bar which carries the nonius scale and index-glass of a quadrant, octant, quintant, or sextant.
"The Sailor's Word-Book" by William Henry Smyth
Excluded, of course, are those instruments normally made of wood, such as the octant and the mariners quadrant.
"Early American Scientific Instruments and Their Makers" by Silvio A. Bedini
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### In news:

The Octant, Chameleon, and Flying Fish hide their deep-sky possessions in the dark realms around the South Celestial Pole.
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### In science:

This shows that there is octant sensitivity for this baseline even after including the uncertainty in δC P and θ23 .
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Therefore, in order to avoid getting an erroneous estimate of octant sensitivity, we take these ‘corrected’ deﬁnitions into account.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
In our calculation, the hierarchy is assumed to be known in all the atmospheric neutrino experiments, since the time-scale involved would ensure that the hierarchy is determined before any signiﬁcant octant sensitivity is achievable.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Figure 5: Marginalized octant sensitivity from a combination of NOνA and T2K, for the case of normal and inverted mass hierarchy.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Figure 6: Marginalized octant sensitivity from a combination of NOνA and T2K, for the case of normal and inverted mass hierarchy.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Figures 5 and 6 depict the octant sensitivity from a combination of NOνA and T2K marginalized over the test parameters and with added priors.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Table 2 lists the values of the octant sensitivity from NOνA and T2K individually and from the combination for a speciﬁc value δ tr C P = 0, and a set of true θ23 values from both octants, without and with added priors, to depict the relative contributions from the two experiments.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
The χ2 values are asymmetric across the lower and higher octants, as can be seen in Table 2.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Figure 7: Octant sensitivity from NOνA appearance and disappearance channels and their combination and from T2K as a function of test θ23 (left panel) and test δC P (right panel). θ13 and δC P are marginalized in the left panel and θ13 and θ23 are marginalized in the right panel.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
The χ2 minima for both appearance and disappearance channels are very low for all values of θ tr 23 , indicating negligible octant sensitivity from the channels separately.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
This is because both T2K and NOνA roughly follow the octant behaviour dictated by the vacuum probabilities with subleading contributions of the δC P -dependent terms.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Note that the addition of priors makes the asymmetry less pronounced since the prior contributions for the lower and higher octants are roughly symmetrical.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Determination of the octant sensitivity of INO using the resolutions obtained from INO simulations is in progress.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Figure 8: Marginalized octant sensitivity from muon events with a magnetized iron detector (500 kT yr exposure), for the case of normal and inverted mass hierarchy.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
Therefore it is plausible to assume that hierarchy would be determined before octant in these detectors.
Octant sensitivity for large theta(13) in atmospheric and long baseline neutrino experiments
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