Visibility Modeling

Deep-Sky Planner Mobile Edition (Dspme) includes mathematical models that predict whether an object can be seen, given a set of equipment and sky conditions. In the case of extended deep-sky objects and single stars, it means whether the object can be detected visually. In the case of a double star, this means whether the pair can be split visually.

These models are the product of several years of research and field testing by the author, and published research by other scientists. These models are intended to provide guidance rather than an absolute answer to the question of whether an object can be seen.

The models require various input parameters in addition to object data. The table below describes the data required by the various models. Important: A model cannot be employed if any of the required input data are missing. Some of the input parameters are objective in nature while a few are rather subjective. If the visibility model is yielding results that seem incorrect given instrument, observer and sky conditions, these subjective parameters might be adjusted for improved results. In particular, you might adjust (in the order of greatest significance): observer's experience level, instrument's cleanliness or observer's dark-adapted eye pupil size.

Object Type	Sky Conditions Required	Equipment/Observer Information Required [The equipment and observer parameters are only adjustable in Deep-Sky Planner Desktop Edition at this time.]
Extended Deep-Sky Objects, Larger Planets	Darkness and transparency	Instrument primary aperture, optical system transmission, eyepiece apparent field of view or binocular true field of view, dark-adapted eye pupil size.
Double Stars	Seeing	Instrument primary aperture, obstruction (if any) and cleanliness (if any), observer's dark-adapted eye pupil size and experience level
Single Stars, Carbon Stars, Asteroids, Smaller Planets		Instrument primary aperture and cleanliness (if any), observer's dark-adapted eye pupil size and experience level
Variable Stars		Instrument primary aperture and cleanliness (if any), observer's dark-adapted eye pupil size and experience level

The result of the models' computations are shown below. These results are labeled Vis Pred on reports.

Object Type	Vis Pred	Comments
Extended Deep-Sky Objects, Larger Planets
	Easy	The object is bright enough to be seen without difficulty.
	Moderate	The object is bright enough to be seen with some difficulty.
	Difficult	The object may be bright enough to be seen. Try to observe this object at its highest altitude in the sky at a dark location, and be sure to use averted vision.
	Improbable	The object is probably too dim to be seen. Try to observe this object at its highest altitude in the sky at a dark location.
	Too dim	The object is too dim to be seen.
	Too low	The object is low in the sky; the model becomes very inaccurate at low altitudes.
	Down	The object is below the horizon
	<blank>	The object can't be modeled due to missing data.
Double Stars
	Easy	Both stars in the pair are bright enough to be seen, and they may be resolved. The two stars appear to be widely separated.
	Moderate	Both stars in the pair are bright enough to be seen, and they may be resolved. The two stars may appear to be fairly close, but they appear to be clearly separated.
	Difficult	Both stars in the pair are bright enough to be seen, and they may be resolved. The two stars may appear to be touching or they may be separated by a hair-line gap.
	Improbable	Both stars in the pair are bright enough to be seen but the pair is so close that it is improbable that they can be resolved. The two stars may appear to be a rod-shaped or figure-8 shaped star.
	No split	Both stars in the pair are bright enough to be seen but the pair is too close to be resolved.
	Sec. dim	The primary is bright enough to be seen but the secondary is not.
	Both dim	Both stars in the pair are too dim to be seen.
	Unmodeled	The stars fall outside the modeled parameters.
	Down	The stars are below the horizon
	<blank>	The stars can't be modeled due to missing data.
Single Stars, Carbon Stars, Asteroids, Smaller Planets
	Visible	The object is bright enough to be seen.
	Too dim	The object is too dim to be seen.
	Down	The object is below the horizon
	<blank>	The object can't be modeled due to missing data.
Variable Stars
	Visible	The star is bright enough to be seen throughout its magnitude range.
	Maybe	The star may be seen when it is at its brightest magnitude, but not at its dimmest magnitude; thus, it may be visible depending on where it is in its light curve.
	Too dim	The star is too dim to be seen even when it is at its brightest magnitude.
	Down	The star is below the horizon
	<blank>	The star can't be modeled due to missing data.

Vis Pred may contain a missing value message that can help you determine why the model isn't computed. These messages are described below. Note that some of the required data items must be set in the Desktop Edition and imported into DSPME.

Category	Message	Meaning	Requires Desktop Edition
Plan	Missing size	Size for this object is not present in the plan document.
Equipment	No instrument	No instrument is selected. Go to Equipment and select an instrument.
	Missing eyepiece pupil	No eyepiece is selected. Go to Equipment and select an eyepiece.
	Missing apparent FoV	The eyepiece selected does not include field of view information.This value cannot be set in DSPME at this time - you must use the Desktop Edition to create this value. In the case of binoculars, the true field of view is missing in the instrument definition.	yes
	Missing obstruction	The instrument selected does not include obstruction information. This value cannot be set in DSPME at this time - you must use the Desktop Edition to create this value.	yes
	Missing transmission	The instrument selected does not include transmission information. This value cannot be set in DSPME at this time - you must use the Desktop Edition to create this value.	yes
	Missing cleanliness	The instrument selected does not include cleanliness information. This value cannot be set in DSPME at this time - you must use the Desktop Edition to create this value.	yes
Conditions	Invalid sky darkness	Sky darkness value is invalid. Go to Conditions and select the sky darkness value.
	Missing seeing Arcsec	No sky seeing value is defined. Go to Conditions and select the sky seeing value.
	Missing AOD	No sky transparency value is defined. Go to Conditions and select the sky transparency value.
Observer	Missing eye pupil	Observer's eye pupil diameter is not defined. Go to Equipment and select an observer that has an eye pupil defined. This value cannot be set in DSPME at this time - you must use the Desktop Edition.	yes
	Missing experience	Observer's experience level is not defined. Go to Equipment and select an observer that has an experience level defined. This value cannot be set in DSPME at this time - you must use the Desktop Edition.	yes