Who Needs to Know Celestial Navigation?
Not every captain license exam covers celestial navigation. Understanding which endorsements require it lets you focus your study time efficiently.
OUPV (6-Pack) — Not Required
The OUPV license (Operator of Uninspected Passenger Vessels) does not test celestial navigation. OUPV authorizes operation of uninspected passenger vessels carrying up to six passengers within near-coastal or inland waters where piloting and electronic navigation are fully sufficient.
- No sextant, no Nautical Almanac on the OUPV exam
- Focus is on chart plotting, COLREGS, and seamanship
- Skip this section if you are pursuing OUPV only
Master 100 GRT — Required for Ocean / Offshore
Master 100 GRT candidates who seek the Oceans or Offshore endorsement must pass celestial navigation questions on the Navigation General module. These endorsements authorize operation beyond the boundaries where GPS backup via traditional celestial methods remains a USCG competency standard.
- Celestial questions appear in Navigation General
- Covers sextant, Nautical Almanac, noon sight, and stars
- Near-coastal Master endorsement does NOT require celestial
| License | Endorsement | Celestial Required | Waters Authorized |
|---|---|---|---|
| OUPV | Near-Coastal | No | Within 100 nm of shore |
| OUPV | Inland | No | Inland waters only |
| Master 100 GRT | Near-Coastal | No | Within 200 nm of shore |
| Master 100 GRT | Offshore | Yes | Beyond 200 nm of shore |
| Master 100 GRT | Oceans | Yes | Unlimited offshore |
The Celestial Sphere: Framework of the Sky
Every concept in celestial navigation is built on a mental model called the celestial sphere. Understanding its geometry makes the rest of the subject — hour angles, declination, the navigational triangle — coherent rather than arbitrary.
Zenith
The point on the celestial sphere directly overhead the observer. Every observer has a unique zenith determined by their geographic position.
Nadir
The point on the celestial sphere directly below the observer, diametrically opposite the zenith. Not used directly in navigation but defines the lower hemisphere.
Celestial Equator
The great circle formed by projecting the earth's equator onto the celestial sphere. Celestial bodies north of it have positive declination; south is negative.
Declination (Dec)
The angular distance of a celestial body north or south of the celestial equator. The exact celestial equivalent of latitude. Tabulated in the Nautical Almanac for every hour.
GHA
Greenwich Hour Angle — the angular distance measured westward from the Greenwich meridian (0 degrees) to the hour circle of a celestial body. Increases at about 15 degrees per hour.
LHA
Local Hour Angle — GHA adjusted for the observer's longitude. LHA equals GHA plus east longitude or GHA minus west longitude. It measures the body's position relative to the observer's own meridian.
SHA
Sidereal Hour Angle — the westward angle from the vernal equinox to a star's hour circle. Used to find a star's GHA: GHA star equals GHA Aries plus SHA star.
Celestial Poles
The north and south celestial poles are the points where the earth's rotation axis, extended, intersects the celestial sphere. Polaris lies near the north celestial pole.
Meridian Passage
The moment a celestial body crosses the observer's meridian, reaching its highest altitude for the day. For the sun, this is local apparent noon (LAN).
The Hour Angle System
Hour angles are measured westward from a reference meridian, in degrees from 0 to 360 (or equivalently in hours, minutes, and seconds since 15 degrees equals 1 hour). The system is the celestial analog of longitude, but it moves: as the earth rotates eastward, GHA of every celestial body increases steadily at approximately 15 degrees per hour (one full rotation in 24 hours).
The Navigational Triangle (PZX Triangle)
The PZX triangle is the geometric heart of celestial navigation. Every altitude computation and line-of-position plot flows from solving this spherical triangle. Understanding its three vertices and three sides is essential for the USCG Master exam.
P — Pole
The elevated celestial pole — north celestial pole for observers in the Northern Hemisphere, south celestial pole for the Southern Hemisphere. The side PZ is the co-latitude of the observer (90 degrees minus latitude), and PX is the polar distance of the body (90 degrees minus declination).
Z — Zenith
The zenith of the observer, directly overhead. The side ZX is the co-altitude of the body (90 degrees minus altitude). ZX is the key unknown when working from the observed altitude to find position. The angle at Z is the azimuth angle (Z), which converts to true azimuth (Zn) by rules depending on the observer's hemisphere and the body's hour angle.
X — Body
The geographic position of the celestial body — the point on earth directly beneath the body. The angle at P is the local hour angle (LHA). Together P, Z, and X define a unique spherical triangle on the celestial sphere that can be solved when any three of the six elements (three sides, three angles) are known.
Solving the Triangle: The Intercept Method
The standard approach on the USCG exam is the intercept method (Marcq Saint-Hilaire method). The navigator does not need to find their exact position to use it — they choose a convenient assumed position (AP) and compute what the altitude and azimuth would be from that position. The difference between observation and computation gives the intercept.
- 1Observe altitude. Take the sextant sight and record the time to the nearest second in GMT. The raw sextant reading is sextant altitude (Hs).
- 2Correct altitude. Apply index error, dip, and the main altitude correction from the Nautical Almanac to get observed altitude (Ho).
- 3Extract almanac data. Find the GHA and declination of the body for the GMT of the sight. Apply the increments for minutes and seconds to get exact GHA.
- 4Choose an assumed position. Select a latitude to the nearest whole degree and a longitude that makes LHA a whole number (simplifies table entry).
- 5Enter sight reduction tables. Use LHA, assumed latitude, and declination to find computed altitude (Hc), azimuth angle (Z), and the d correction factor from H.O. 229 or H.O. 249.
- 6Compute intercept. a equals Ho minus Hc, in minutes of arc. Positive intercept means Ho is greater than Hc: plot toward the body (T for Toward). Negative: plot away (A for Away).
- 7Plot the LOP. From the assumed position on the chart, draw the true azimuth line (Zn). Mark the intercept distance along that line. Draw a perpendicular through that point — that perpendicular is the line of position.
The Sextant: Instrument of Celestial Observation
The sextant measures the angle between a celestial body and the visible horizon. That angle — the sextant altitude — is the raw data from which every celestial calculation begins. USCG exam questions cover sextant parts, adjustments, corrections, and technique.
Principal Parts
Errors and Adjustments
Index Error (IE)
Set the sextant to zero and observe the horizon. If the horizon appears as two separate lines rather than one, index error exists. Read the micrometer: if the reading is on the arc (positive numbers), IE is subtracted from all readings. If off the arc (negative), IE is added. Small IE is corrected arithmetically; large IE requires adjusting the horizon mirror.
Perpendicularity Error
The index mirror must be perpendicular to the plane of the arc. Check by holding the sextant horizontally and looking across the arc — the arc and its reflection in the index mirror should appear as a continuous line.
Side Error
The horizon mirror must also be perpendicular to the plane of the arc. Set the index arm to zero and observe a star — if two images appear side by side rather than vertically aligned, side error exists. Correct by adjusting the horizon mirror with the side-error screw.
Parallax in the Telescope
The telescope must be focused so that the crosshair and the celestial image are at the same focal plane. Move your eye side to side — if the image shifts relative to the crosshair, refocus until no apparent movement exists.
Altitude Correction Chain: Hs to Ho
Every celestial sight requires a series of corrections before the sextant altitude (Hs) becomes the observed altitude (Ho) used in calculations. Each correction accounts for a physical phenomenon that separates the measured angle from the true astronomical angle.
The Noon Sight: Latitude by Meridian Passage
The noon sight (latitude by meridian altitude) is the oldest and most straightforward celestial technique. It requires no knowledge of longitude, no assumed position, and no sight reduction tables. For centuries it was the primary method mariners used to determine latitude at sea.
What Happens at Meridian Passage
As the sun moves westward across the sky each day, it reaches its highest point when it crosses the observer's meridian (the line of longitude through the observer's position). At that moment:
- The sun is due north or due south (true azimuth is 180 or 000)
- The sun's altitude is at its maximum for the day
- The rate of altitude change momentarily equals zero
- The sun's LHA equals exactly 0 degrees (or 360 degrees)
Predicting Local Apparent Noon
To be ready with the sextant, predict LAN before it happens:
- 1. Find the time of meridian passage for the sun from the Nautical Almanac daily pages (labeled Mer. Pass.)
- 2. Apply a longitude correction: 4 minutes per degree of longitude (add for west longitude, subtract for east longitude)
- 3. The result is the GMT of LAN; convert to ship's time using the zone description
- 4. Begin tracking altitude about 15 minutes before predicted LAN
Noon Sight Latitude Formula
Once you have the maximum altitude (Ho at meridian passage), latitude is calculated directly. The formula depends on the relationship between the observer's hemisphere and the sun's declination.
Same Name (Sun and Observer Same Hemisphere)
When the sun's declination and the observer are both north or both south:
Example: Ho equals 68 deg 30 min, Dec N 20 deg 15 min, observer in Northern Hemisphere. Lat = 21 deg 30 min N plus 20 deg 15 min N = 41 deg 45 min N.
Contrary Name (Sun and Observer Opposite Hemispheres)
When the sun's declination is opposite to the observer's hemisphere:
Example: Ho equals 72 deg 10 min, Dec S 15 deg 30 min, observer in Northern Hemisphere. Lat = 17 deg 50 min minus 15 deg 30 min = 2 deg 20 min N.
Technique at the Sextant
Do not try to take a single snap observation at the predicted LAN time. Instead, begin tracking the sun about 10 to 15 minutes before predicted LAN. As the sun nears its maximum, take a series of readings every minute or two. The sun will appear to hang at the same altitude for several minutes before beginning to descend — that maximum reading is the meridian altitude. Some navigators use the "rocking the sextant" technique: tilt the sextant side to side so the sun traces an arc; the bottom of the arc is the true altitude at that moment. Record the highest consistent reading as the meridian altitude.
Sight Reduction Tables: H.O. 229 and H.O. 249
Sight reduction tables pre-compute the solution to the PZX navigational triangle. Given three known quantities — assumed latitude, declination, and LHA — the tables return the computed altitude (Hc) and azimuth angle (Z). The USCG Master exam primarily references H.O. 229.
H.O. 229 — Sight Reduction Tables for Marine Navigation
The standard marine sight reduction publication. Organized in six volumes by latitude bands (0 to 15, 15 to 30, 30 to 45, 45 to 60, 60 to 75, 75 to 90 degrees). Each page covers a specific LHA value.
- Inputs: Assumed latitude (whole degree), LHA (whole degree), declination (whole degree, entered with interpolation for minutes)
- Outputs: Hc (computed altitude in degrees and minutes), d (altitude difference for declination interpolation), Z (azimuth angle in degrees)
- d correction: Multiply d by the declination minutes and divide by 60 to get the correction to Hc
- Z to Zn: Convert azimuth angle Z to true azimuth Zn using the rules printed at the top of each H.O. 229 page
H.O. 249 — Sight Reduction Tables for Air Navigation
Originally designed for aerial navigation, H.O. 249 is also widely used at sea because of its speed and simplicity. Three volumes cover different uses.
- Volume 1: Selected stars only — 41 stars precomputed for each degree of latitude and LHA of Aries. Fastest possible star sight reduction; no declination interpolation needed.
- Volumes 2 and 3: Cover sun, moon, planets, and stars for latitudes 0 to 89 degrees. Similar format to H.O. 229 but less precise (Hc to whole minutes only).
- Exam use: The USCG Master exam may reference either publication. Know how to use both and understand the key difference in precision.
H.O. 229 Step-by-Step Procedure
Polaris: Direct Latitude in the Northern Hemisphere
Polaris (Alpha Ursae Minoris, the North Star) is one of the most useful celestial bodies for navigation because its altitude above the horizon is nearly equal to the observer's latitude. This makes a Polaris sight one of the fastest ways to determine latitude without solving the full PZX triangle.
Why Polaris Works
Polaris is located within about 0.75 degrees of the north celestial pole. If it were exactly at the pole, its altitude above the horizon would be exactly equal to the observer's latitude with no further correction. Because it is not quite at the pole, it traces a small circle around the pole once per day — its altitude varies slightly above and below the pole's altitude during the course of each sidereal day.
Three small corrections — a0, a1, and a2 — account for this offset. These are tabulated in the Polaris Tables at the back of the Nautical Almanac as a function of LHA of Aries (the position of the vernal equinox, which governs the orientation of the celestial sphere at any given time).
Polaris Latitude Formula
Where Ho is the corrected sextant altitude of Polaris (applying index error, dip, and star altitude correction), and a0, a1, a2 are corrections from the Polaris Tables entered with LHA of Aries, the observer's estimated latitude, and the month of the year.
Finding Polaris in the Sky
Polaris is not the brightest star in the sky — it is only magnitude 2.0, similar to the stars of the Big Dipper. Navigators find it by using the two pointer stars at the outer edge of the Big Dipper (Dubhe and Merak). Draw a line from Merak through Dubhe and extend it about five times the distance between those two stars. Polaris will be at the end of that line. It appears to sit almost motionless while all other stars circle around it through the night.
- Clear skies at any latitude north of the equator
- Civil or nautical twilight (horizon and stars both visible)
- At high latitudes it is visible all night throughout the year
- Near the equator it is very low and difficult to observe reliably
- Only useful in the Northern Hemisphere (not visible south of about 2 degrees S)
- Requires clear skies and a visible horizon
- Provides latitude only — a separate LOP is needed for a complete fix
- The a0 correction varies from about 0.5 to 1.5 degrees depending on LHA Aries
Navigational Star Identification
The Nautical Almanac lists 57 selected navigational stars — bright enough to sight reliably and distributed well across the sky. The USCG exam tests star identification by constellation membership, appearance, and position relative to other prominent stars. At twilight, a navigator typically identifies and shoots three to five stars for a reliable celestial fix.
Polaris
Mag 2.0North Star. Found by extending a line from Merak through Dubhe (Big Dipper pointer stars) by five times their separation. Always within 1 degree of true north. Gives latitude directly.
Sirius
Mag -1.5Brightest star in the night sky. Blue-white. Visible in the Northern Hemisphere winter. Found by following the belt of Orion southeastward.
Canopus
Mag -0.7Second brightest star in the night sky. Far south — visible from latitudes south of about 37 degrees N. Important for Southern Hemisphere navigation.
Arcturus
Mag -0.1Brightest star in the Northern Hemisphere sky. Orange-red. Found by following the arc of the Big Dipper handle (arc to Arcturus). Prominent in spring and summer.
Vega
Mag 0.0Brilliant blue-white star. Third brightest in the night sky for Northern Hemisphere observers. Forms the Summer Triangle with Deneb and Altair. Prominent in summer.
Capella
Mag 0.1Bright yellow star. Circumpolar at latitudes above about 44 degrees N. High in the northern sky in winter. Nearly the same declination as the equator for planning star sights.
Rigel
Mag 0.1Blue-white supergiant at the foot of Orion. One of the brightest stars visible in winter. Its declination of about 8 degrees S makes it accessible to both hemispheres.
Betelgeuse
Mag 0.5Distinctive red-orange supergiant at the shoulder of Orion. Contrasts sharply with blue-white Rigel. Helps confirm identification of Orion in the sky.
Aldebaran
Mag 0.9Orange-red giant. The eye of Taurus (the Bull). Found by following Orion's belt northwestward. Bright enough to identify even in hazy conditions.
Using H.O. 249 Volume 1 for Star Sights
H.O. 249 Volume 1 precomputes the 41 best stars for each degree of latitude and each degree of LHA Aries. At twilight, the navigator calculates the current LHA of Aries, enters Volume 1 with that value and their assumed latitude, and reads off the expected altitude and azimuth for the best available stars. This allows the navigator to pre-set the sextant and look in the right direction before the star becomes visible.
Compass Check by Azimuth of the Sun
A compass check by azimuth is a routine offshore procedure that compares the computed true azimuth of the sun with the observed compass bearing. The difference reveals compass error — the combined effect of variation and deviation. USCG exams test this procedure as a practical seamanship skill.
Computing True Azimuth (Zn)
True azimuth of the sun is computed using H.O. 229 (or azimuth tables in the publication), entering with LHA, assumed latitude, and declination — the same inputs used for a sight reduction. The tables return Z (azimuth angle), which is then converted to Zn (true azimuth) using the Z-to-Zn conversion rules.
Alternatively, an amplitude calculation can be used at sunrise or sunset, when the sun is on or near the horizon and its amplitude (angle from east or west) can be directly compared to the compass bearing.
Finding Compass Error
If Zn is greater than Zc, compass error is East (the compass reads too low — apply the error to the right). If Zn is less than Zc, compass error is West. Total compass error equals variation plus deviation; if variation is known from the chart, deviation can be extracted. Record compass error in the deck log at least once per watch offshore.
Amplitude Method at Sunrise and Sunset
When the sun is on the visible horizon (rising or setting), its amplitude is the angle from due east (rising) or due west (setting) to the sun's bearing. Amplitude is tabulated in Bowditch or the azimuth tables as a function of declination and latitude. To get true azimuth from amplitude: for a rising body, true azimuth is 90 degrees minus amplitude (if north declination) or 90 degrees plus amplitude (if south declination). The amplitude method is fast and requires no watch correction — just note the exact moment the lower limb of the sun touches the horizon and read the compass bearing at that instant.
Running Fix and the Sun-Run-Sun Fix
During daylight at sea, the navigator usually has only the sun available as a celestial body. A single sun sight gives one line of position — useful for a running fix when combined with a later sight, after advancing the first LOP along the vessel's track.
The Running Fix Concept
A running fix uses two LOPs taken at different times. The first LOP is advanced along the course and speed of the vessel until the time of the second LOP. The advanced LOP is then crossed with the second LOP to produce a fix. The accuracy of the fix depends entirely on the accuracy of the track run between sights — any error in course or speed introduces proportional error in the fix.
To advance an LOP: move every point on the line in the direction of course made good by a distance equal to the distance run between sights. Equivalently, advance the assumed position by the vector of travel and redraw the LOP through the new assumed position with the same intercept and azimuth.
The Sun-Run-Sun Fix
The sun-run-sun fix is the most common running fix technique offshore. A morning sun sight (when the sun is in the east at a low-to-moderate altitude) provides an LOP running roughly north-south. The vessel continues on its track. At or near noon, a meridian altitude (noon sight) provides the latitude — a horizontal LOP. The morning LOP is advanced to noon. Where the advanced morning LOP crosses the latitude line from the noon sight is the noon position.
A further afternoon sun sight (when the sun is in the west) can be crossed with the advanced noon latitude line to produce an afternoon fix. The cycle can continue: morning LOP, noon sight, afternoon LOP, giving two fixes per day from the sun alone.
Sun-Run-Sun Procedure Step by Step
- 1Morning sight. Take a sun sight when the sun is between about 20 and 60 degrees altitude in the morning. Reduce it to an LOP using H.O. 229 or H.O. 249. Plot the LOP on the working chart relative to the assumed position.
- 2Track the run. Record the course steered and speed logged from the time of the morning sight to the time of the noon sight. Compute the distance run. Apply any current if known.
- 3Noon sight. At LAN, take the meridian altitude and compute latitude. Plot the latitude line (an east-west line) on the chart.
- 4Advance morning LOP. Move the morning LOP in the direction of course made good by the distance run. Transfer the entire line (keep same intercept angle to azimuth; move the line parallel to itself along the track vector).
- 5Identify the noon fix. The intersection of the advanced morning LOP and the noon latitude line is the noon running fix. Label it with the time and mark it on the chart as a running fix (not a simultaneous fix).
Greenwich Mean Time, Chronometers, and Time Errors
Accurate time is the foundation of celestial navigation. The GHA of every celestial body changes continuously — at roughly 15 degrees per hour, or 0.25 degrees per minute, or 0.004 degrees per second. A one-second time error produces about 0.25 nautical miles of position error at the equator. Rigorous time discipline is not optional.
The Marine Chronometer
A marine chronometer is a high-precision timepiece kept permanently set to GMT (UTC). It is mounted in a gimbaled box to remain level at sea and is wound at the same time each day. The chronometer's daily rate (how many seconds it gains or loses per day) is recorded and applied as a correction. A known chronometer error (CE) is also applied: CE equals chronometer reading minus correct GMT.
Watch Time and Zone Time
At sea, the ship keeps a zone time based on its longitude (one zone for each 15 degrees of longitude, centered on multiples of 15 degrees). Zone description (ZD) is the number of hours to add to zone time to get GMT: positive for west longitudes, negative for east. Ships often advance or retard clocks by one hour as they cross each 15-degree meridian, typically at midnight to minimize disruption to the watch schedule.
Time Signals and Radio Checks
The chronometer should be compared to a reliable time signal at least once per day at sea. Time signals are broadcast by radio stations WWV (Colorado) and WWVH (Hawaii) in the United States on 2.5, 5, 10, 15, and 20 MHz. GPS receivers display GPS time (essentially UTC) and can serve as an accurate time reference when operating. The difference between the chronometer reading and the time signal gives the chronometer error for that day.
Recording the Sight
When taking a celestial sight, the procedure is: one person manipulates the sextant and calls "Mark" when the image is set; a second person reads the stopwatch and records the time to the nearest second. The sextant reading is then recorded from the drum micrometer. Multiple sights are taken and averaged for accuracy. If working alone, set the sextant on a celestial body, then read time and altitude simultaneously — or use the averaged-sights technique of tracking the body and noting the altitude at an exact minute mark.
USCG Exam Strategy for Celestial Navigation
The Master 100 GRT celestial navigation questions on the USCG exam appear in the Navigation General module for Ocean and Offshore endorsements. Understanding the exam format helps you allocate study time efficiently.
High-Frequency Topics
- 1.GHA and LHA calculation from the Nautical Almanac — daily pages and increments tables
- 2.Altitude corrections: index error, dip, main altitude correction for sun lower limb and stars
- 3.Intercept computation: Ho minus Hc, Toward or Away, nautical miles equal to arc-minutes
- 4.Noon sight latitude formula with same name and contrary name declination
- 5.Polaris latitude procedure and the a0, a1, a2 corrections
- 6.Navigational star identification by constellation and distinguishing features
- 7.H.O. 229 table entry procedure and d correction interpolation
- 8.Z to Zn conversion rules for Northern and Southern Hemisphere
Common Exam Traps
| Topic | Reference | Key Rule |
|---|---|---|
| GHA from almanac | Nautical Almanac daily pages + increments | Hourly GHA plus correction for minutes and seconds |
| LHA calculation | Observer's assumed longitude | West: LHA = GHA minus longitude. East: LHA = GHA plus longitude |
| Dip correction | Nautical Almanac, inside front cover | Always subtracted. Based on height of eye in feet or meters |
| Sun altitude correction | Nautical Almanac, inside front cover | Lower limb: positive correction. Upper limb: negative correction |
| d correction in HO 229 | H.O. 229 interpolation table | d times declination minutes divided by 60. Sign from table |
| Z to Zn, North lat | H.O. 229 top of page | LHA greater than 180: Zn = Z. LHA less than 180: Zn = 360 minus Z |
| Noon sight latitude | Nautical Almanac declination | Same name: add Dec. Contrary name: subtract Dec |
| Polaris latitude | Nautical Almanac Polaris Tables | Ho minus 1 degree plus a0 plus a1 plus a2 |
Frequently Asked Questions
Common questions from Master 100 GRT candidates studying celestial navigation for the USCG exam.
Does the OUPV (6-Pack) license test celestial navigation?⌄
What is the difference between the celestial sphere's zenith and nadir?⌄
What is declination and how does it relate to latitude?⌄
What is the PZX triangle and why does it matter?⌄
How do you convert Z to Zn using H.O. 229?⌄
What does Ho Mo To mean in celestial navigation?⌄
Why is height of eye needed for the dip correction?⌄
What is a circle of equal altitude?⌄
When is a noon sight more accurate than a regular sight reduction?⌄
What is the d correction in H.O. 229 and how is it applied?⌄
What causes the sun's declination to change through the year?⌄
What is GHA Aries and why does it matter for star sights?⌄
How many lines of position do you need for a celestial fix?⌄
What is the best time of day to take star sights?⌄
What is the difference between true azimuth and azimuth angle?⌄
Related Celestial Navigation Topics
Celestial Navigation — Full Guide
Sextant use, Nautical Almanac, noon sight, Polaris, and star identification for the Master 100 GRT exam.
Advanced Celestial Navigation
Moon sights, planet identification, multiple-body fixes, and advanced sight reduction techniques.
Celestial Navigation Exam Questions
Practice problems covering GHA, LHA, intercept calculation, and the full sight reduction process.
Chart Plotting Exam Guide
Dead reckoning, compass error, tides and currents, and position fixing techniques.
Navigation Study Guide
Comprehensive navigation review covering electronic navigation, piloting, and offshore passage planning.
Master 100 GRT License Guide
Full walkthrough of the Master 100 GRT license requirements, exam modules, and endorsement options.
Practice Celestial Navigation Questions Now
NailTheTest has hundreds of USCG exam-style questions covering GHA, LHA, altitude corrections, sight reduction, noon sight, Polaris, and star identification. Study the concepts on this page, then put them to work with timed practice questions in the same format as the actual USCG exam.