Follow

Visual Search

Visual search provides a quick and simple way to find a date when the sun or moon will appear at an azimuth and altitude you specify.

Visual Search offers two modes, Basic and Advanced:

In Basic mode, the following options are available:

Body Choose sun or moon
Illumination

Choose any, crescent, full or custom

Crescent corresponds to when the moon is between 0% and 15% illuminated; full to when it is between 95% to 100% illuminated. These values are preselected to correspond to typical perceptions of what appears 'crescent' or 'full', rather than the precise astronomical definitions.

Illumination range %

If moon is selected and illumination is set to custom, enter the desired custom illumination range here

Find

Choose Rise/Set or Az/Alt

Rise/Set requires only an azimuth as input, whereas Az/Alt allows you to specify both azimuth and altitude

Target altitude °

If Az/Alt is selected, enter the target altitude above the horizon

Target azimuth °

Enter the target azimuth relative to either true north or magnetic north, depending on the app settings

Tolerance ± °

In basic mode, this refers to the allowable tolerance in azimuth.

Start date

The date from which to start the search

Duration

The period of time for which to search

Perform search

Tap this to perform the search

 

Setting search parameters visually

  

You can set the target azimuth and altitude visually using the secondary map pin (hence 'visual search').

With geodetics enabled, and the secondary map pin positioned, the target azimuth and altitude fields are populated automatically from the geodetics results, making it simple to drop the pin behind some mountains, navigate to visual search and find when the sun will above just on the highest point along the line of sight.

All searches are performed for the current primary pin location, so ensure that is set to the desired location beforehand.

Search parameters

Rise/Set search will check rise/set times, adjusted for elevation above the horizon if configured, for the duration of the search and returns any matches that fall within target azimuth tolerance.

Az/Alt search will find times when the sun or moon lies at the target altitude and returns any matches that fall within target azimuth tolerance. In almost all cases, the target altitude is found to within 0.25° or better.

When Advanced mode is enabled, the following additional options are shown:

Phase

Choose Any, Waxing or Waning

For example, to find only truly 'new' moons, choose Crescent and Waxing.

During

Choose Any, Best, Civil or Custom

This setting restricts results for Moon searches based on the altitude of the sun. Best corresponds to when the sun is between +2% and -2% altitude, i.e. the time right around sunset. Civil corresponds to a sun altitude between 0° and -6°, that is, the period of civil twilight.

Align disc

This setting adjusts the search to account for the apparent disc size of the sun or moon when finding altitude. For example, if you want to find times when the moon appears to be 'sitting' on top of a building, you would align to the bottom of the disc rather than the centre. The adjustment takes into account variations in the semidiameter of the sun and moon through the year (e.g. 'supermoon' is 14% larger than 'micromoon').

Priority

Choose Altitude or Azimuth.

When altitude priority is selected, the algorithm finds matching altitudes and then tests azimuth. With azimuth priority, azimuth is found and then altitude is tested against the target and tolerance.

Consider changing priority to match whichever alignment is the most critical for your shot. For example, to catch the moon rising above a mountain peak, altitude is likely more important than azimuth. To align the moon directly behind a statue, azimuth is likely the most important consideration.

 

Results

The result page lists all matches found for the search period. All results shown match the input parameters and tolerance. Results that match the input targets within 0.25° are highlighted with a green icon. Tap any result to set the selected date and time and view the result on the map.

The example below shows results of a search for a crescent moon at a specified azimuth and altitude. In addition to the az/alt of the moon, the moon's percent illumination and percent size above extreme apogee are shown for each result:

IMG_E6DADC902EEB-1.jpeg

Not all searches will generate results. You will never find the sun rising due north in London, for example. Not all input parameter combinations are valid: you will never find a waxing crescent moon rising at 90° during civil twilight. A basic understanding of moon phases can help you to set up search parameters correctly.

You may wish to increase the tolerance above the default 2° if you have trouble obtaining results. For reference, the approximate apparent diameter of the sun or moon is 0.5°, hence a tolerance of ±2° corresponds to ±4 sun/moon diameters. Equally, you can reduce this tolerance for shots that require a tighter alignment.

Tips

If planning a shot that requires a specific sun or moon alignment, you may find few results if the tolerance is set too tight.

Always consider what flexibility in shooting position is available to you.

For example, azimuth alignment is critical in order to align the moon behind a statue. However, you may be able to obtain the desired shot with a range of possible altitudes by moving closer to or farther from the subject.

Az/Alt searches work by interpolating the 'priority' input (altitude or azimuth) to obtain, a high accuracy match (within ±0.05° in most cases). The corresponding input (e.g. azimuth in the case of altitude priority), is then inspected and tested against the target value and tolerance. As noted above, you can choose priority based on your planned shot requirements.

However, in specific circumstances, on mode may give better results than other, based on the rate of change of the values through the day. For example, an azimuth priority search in Singapore in the middle of the day may work less well than an altitude priority search, as the azimuth of the sun or moon tends to change extremely quickly as the body passes overhead.

Was this article helpful?
0 out of 0 found this helpful
Have more questions? Submit a request

0 Comments

Please sign in to leave a comment.
Powered by Zendesk