Record a Horizon Profile for Astrophotography

Record a horizon profile by measuring the direction and angular height of obstructions from one observing position. Keep the north reference consistent, sample extra points at edges and gaps, and save the measurement method and uncertainty with the notes. You can then compare a target's direction and altitude with the obstruction in that same direction.

Fix the observing position and height

Scout in daylight where possible. Set up where you intend to shoot, then label that exact position in your notes. Include the height of the camera lens or telescope's optical opening. A nearby parking pin alone may not distinguish two tripod positions with different views past a tree or wall.

Make the measurements from that position and approximately the same sighting height as the optic. If you move to get a better view, record a separate setup position and recheck the affected directions. A profile recorded standing beside a low camera can misrepresent what the camera sees.

The ESO horizon-obstruction documentation emphasizes keeping the full telescope opening unshaded. Apply that physical check too: a sightline from your eye does not establish that the whole lens or telescope opening clears a nearby fence.

Use one north reference and angular scale

Use azimuth for direction around the horizon and altitude, or elevation angle, for height above the horizontal. The U.S. Naval Observatory describes azimuth measured clockwise, usually from true north. With that convention, north is 0°, east 90°, south 180°, and west 270°. Record the convention rather than assuming every tool uses it.

Keep target coordinates and obstruction measurements on the same north reference. NOAA explains magnetic declination as the location- and time-dependent angle between magnetic and true north. To convert a magnetic bearing to a true bearing, add the signed declination: east is positive and west negative, then wrap the result into a full circle. If a tool already supplies true-north bearings, do not apply that correction again.

Angular height is not elevation above sea level. A phone's location elevation does not tell you the angle to a treetop. Choose a documented sighting clinometer or inclinometer for that measurement, and a bearing tool for direction.

Measure the obstruction direction and height

Prepare the tools. Follow the angular tool's leveling and zero-check instructions. Identify its actual sighting line; a device's tilt reading only helps if it corresponds to the line you are aiming along.
Return to the recorded position and sighting height. Keep the setup fixed while measuring each feature.
Take the direction. Face the obstacle edge or top you want to record and read its azimuth using your chosen north reference.
Take the angular height. From the same position, sight along the clinometer's documented aiming line to the top of that obstruction. Read the elevation above a level horizontal line. The sloping ground or an uneven skyline is not your zero reference.
Repeat and label the reading. Note the obstacle and method. If readings vary, record the spread or mark the result as approximate rather than writing unsupported precision.

If you use iPhone Compass for bearings, Apple's instructions explain holding it flat and note that magnetic or environmental interference can affect accuracy. Check readings away from sources of interference, following the tool's guidance. A bearing reading and a treetop elevation-angle measurement remain separate tasks.

A reference photo can help identify which branch, roof edge, or ridge you measured. Keep its orientation and setup label with it. A casual panorama alone does not establish calibrated angular heights.

Sample edges and gaps

Sweep your view around the horizon while keeping the measuring position fixed. Record the upper obstruction boundary in the directions relevant to your subject, and continue around the full circle if you want a general profile. Stellarium's landscape documentation uses measured azimuth–altitude pairs to describe a horizon line; the same pairing makes useful field notes.

Broad obstructions: record enough directions to show how a ridge or treeline changes height.
Sharp edges: add readings where a building begins or ends, or a ridge rises abruptly.
Narrow gaps: record both sides and inspect the opening itself. A gap between two samples is not automatically clear.
Overhanging branches or openings under an obstacle: add a note or sketch. A simple upper-boundary profile cannot represent every shape.
Unmeasured directions: leave them marked as unknown in your field record.

Choose the sampling density for the actual features. Sparse points can miss a narrow chimney, branch, or peak. Connecting those points in a sketch or software model does not verify the intervening view.

Copy the horizon worksheet

Keep a setup record and a repeatable row for each measurement. Use degrees throughout if that is what your tools and planning source require.

Setup record
Field	What to record
Observing position	Spot label and enough position detail to place the tripod there again.
Optic and sighting height	Equipment setup and the measurement height used.
Date and conditions	When checked, plus foliage or temporary obstructions that affect the view.
North reference	True or magnetic; any correction applied, with its source and date.
Measurement method	Bearing tool, angular tool, leveling or zero check, and known limitations.

For each sample, copy these fields:

Azimuth: the direction of this reading, with its north reference.
Obstruction elevation angle: the upper edge above the level horizon.
Feature: the branch, ridge, building, or other edge being measured.
Extent: any separately measured start and end directions for that feature.
Uncertainty: repeat-reading variation, rough estimate, or a known limitation of the tool.
Follow-up: a missing direction, gap to inspect, or photo or sketch reference.

A hypothetical clearance calculation

This is an invented angular example, not an observation or a prediction for a real location. Suppose a target's center has an altitude of 22° and the recorded treetop in that same direction is 18° above the horizontal.

Nominal center clearance

22° − 18° = 4° above the recorded edge.

The result compares one representative point with one obstruction reading. It does not show that the lower edge of an extended target, the Moon's limb, or the full camera frame clears the trees. Check the object's angular extent and your intended framing. For a panorama, inspect the entire sweep.

Also account for uncertainty in both direction and height. A slightly different bearing can meet a taller branch, and a different tripod position or height changes the comparison. Choose an allowance justified by the measurements and composition; there is no universal clearance margin that fixes uncertain data.

Finally, one clear comparison does not establish a continuously clear interval. The target changes direction and altitude through the session, so compare its path with the profile and inspect intervening obstructions. Use the target-window guide for the separate timing decision.

Recheck the real view

Return to the recorded setup position and optic height.
Confirm the north reference and the part of the profile your target will cross.
Look for changed foliage, vehicles, construction, or other temporary obstructions.
Check the whole optical opening, target extent, and intended frame.
Review the relevant path through the session, including gaps between measurements.
Update the notes when the view or measuring position changes.

ESO's obstruction guidance specifically notes that growing trees can require updates. A profile is a dated record of this setup, not a permanent description of every position at the location.

Save manual obstruction sectors in DarkScout

After recording the view, save an editable observing spot in DarkScout and enter its obstruction sectors manually. Each sector describes a direction range with one minimum altitude across it. The current editor supports up to eight sectors and obstruction altitudes from 0° to 60°. Keep features beyond those limits in your field notes and check them on site. These are a simplified planning input; keep the detailed samples, optic height, north-reference notes, and uncertainty in your worksheet.

For a changing skyline, split the directions into meaningful sections rather than treating one reading as the height of a whole ridge. Overlapping sectors use the higher limit, and directions without an entered sector have no added obstruction limit. An unentered direction therefore needs an on-site check too.

Use the profile alongside target visibility, cloud, Moon, and location planning. A displayed planning window does not guarantee continuous clearance for the entire target or camera frame; check which target and conditions it describes and confirm the actual view before shooting.

The current App Store listing includes horizon profiles among DarkScout's free features. The app requires iOS 26 or later. You can use the field worksheet above with your preferred measuring and planning tools.

Plan from a spot you know.

Keep observing locations, entered obstructions, and night conditions together.

Get DarkScout for iPhone All features free · iOS 26 or later

Sources and further reading

Published October 19, 2026. Coordinate definitions, measurement references, and current product claims checked for this guide. The 22°/18° example is hypothetical and contains no field-test or geographic prediction.