Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

accuracy - comet ephemeris

Comet positions are completely dependent on the orbital elements used to calculate the ephemeris.  The Minor Planet Center updates orbital elements periodically for objects as the models are refined by observations.  Be sure your orbital elements are updated to get the most accurate ephemeris calculations.  For newly discovered comets, orbital elements may be updated daily; for well studied comets, the updates are once or so per year.

accuracy - darkness

Rise, set, and twilight times are in error up to a couple minutes. Note that the true times are further affected by the observer's local conditions - air temperature, air pressure, and local horizons, so that even a perfectly calculated time would probably be in error at a given location by a minute or more. Lunar phase is in error by less than .14%. For a detailed discussion, see Accuracy.

accuracy - deep-sky & stars

Size and magnitude are given to the same accuracy found in the original catalog. Positions are precessed where necessary to epoch and mean equinox of J2000.0. Rise, set, and transit times are in error less than a couple minutes. For a detailed discussion, see Accuracy.

accuracy - asteroid ephemeris

Asteroid positions are completely dependent on the orbital elements used to calculate the ephemeris.  The Minor Planet Center updates orbital elements periodically for objects as the models are refined by observations.  Be sure your orbital elements are updated to get the most accurate ephemeris calculations.  For newly discovered asteroids, orbital elements may be updated daily; for well studied asteroids, the updates are once per year or so.

accuracy - planet ephemeris

Positions of the Sun and the planets Mercury through Neptune are in error by less than a few arc seconds. Magnitudes may be in error by as much as a few tenths.

Pluto data is accurate for the years 1885 to 2099. Error in position is < 1 arc second, distance to the Sun < .00002 au.

The error in the position of the Moon is < 11 arc seconds. The phase of the moon is in error by < .14%

accuracy - planet events

The times of planet events are accurate for modern times, not those in the distant past or future. The error in the times calculated may be as large as:

airmass

Airmass is the relative amount of atmosphere through which light must travel from a celestial object to the observer, where 1.0 is the minimum achieved by looking at the zenith (altitude 90 degrees.) Deep-Sky Planner uses the model presented by G. V. Rozenberg (1966) to calculate airmass.

altitude

Altitude is the vertical component of horizontal coordinates, the horizontal component being azimuth. The altitude of a point is measured from the horizon (0°) to the zenith (90°). An altitude less than 0° is below the horizon. It is possible to see an object as much as 0°.5667 below the horizon because of atmospheric refraction.

altitude at transit

Altitude at transit is the altitude of an object when it crosses the observer's meridian. Therefore, it is the maximum altitude that the object reaches in the sky on a given day. Note that the calculation of this angle includes the effect of atmospheric refraction which is -34' or -0°.5667. Theoretically, it is possible to have a transit altitude as small as -0°.6.

apparent equatorial coordinates

Apparent coordinates describe the position of a celestial object as precessed to the epoch and equinox of date (Now). Apparent positions of sun, moon and planets are further corrected for aberration, nutation and parallax (topocentric apparent equatorial coordinates).

apparent field

Apparent field is the angular diameter of a view seen through the field stop of an eyepiece from the observing position.

astrometric equatorial coordinates

astrometric coordinates describe the position of a celestial object precessed to a standard epoch and equinox such as J2000.0.

Astronomical Algorithms

Meeus, Jean, Astronomical Algorithms, Willmann-Bell, Inc, 1991.

The author wishes to thank Willmann-Bell, Inc. for granting permission to use the software that accompanies Astronomical Algorithms:

This program includes routines from Astronomical Algorithms Software, copyright © 1991 by Jeffrey Sax which is an option to the book Astronomical Algorithms by Jean Meeus, copyright (c) 1991 by Willmann-Bell, Inc. ISBN 0-943396-35-2.

Nonexclusive use has been granted specifically, in writing, by Willmann-Bell, Inc. for use in this program. Serial number UC55881c.

astronomical darkness

Astronomical darkness occurs when the moon is below the horizon and the sun is 18° or more below the horizon.

astronomical twilight

Astronomical twilight occurs when the Sun is 18° below the horizon.

atlas references

Reference information is available in Deep-Sky Planner reports for several popular atlases (see below.) You can select objects on an atlas page in any of the search reports, and you can disable any atlas throughout the product if you don't use it.

Supported Atlases:

▪Sky Atlas 2000.0

▪Uranometria 2000.0

▪Millennium Star Atlas

▪interstellarum Deep-Sky Atlas
 

▪Herald-Bobroff AstroAtlas

▪Uranometria 2000.0 2d Ed

▪Pocket Sky Atlas

atmospheric extinction

Atmospheric extinction is the loss of light as it passes through the atmosphere, ostensibly from a celestial source. Light is lost due to absorption and scattering. Water molecules absorb infrared light; ozone and oxygen molecules absorb ultraviolet light. Air molecules, aerosols and fine particulate matter scatter light. These factors taken together affect the ability to see or image an object due to local circumstances caused by atmospheric extinction.

Deep-Sky Planner uses an aerosol optical depth measurement to calculate extinction due to aerosol scattering. If this value is unavailable, an estimate of 0.12 magnitudes per airmass is used, as proposed by D. W. E. Green (1992).

azimuth

Azimuth is the horizontal component of horizontal coordinates, the vertical component being altitude. The azimuth of a point is measured by astronomers from due south (0°) to due west (90°), and so on. Navigators measure azimuth from due north (0°) to due east (90°), and so on. The program allows you to select either format as a convenience.

B

Bautz-Morgan type

Bautz-Morgan system describes the morphology of galaxy clusters:

Best time

Best time is the time at which a deep-sky or stellar object reaches its highest altitude during the viewing time you have selected.
 

Brightness

Brightness is a relative value used in some catalogs instead of magnitude. The codes are:

C

central star magnitude

Central Star Magnitude is the photographic magnitude of the central star of a planetary nebula.

chart numbers

The following sky atlases contain the given number of charts:

civil twilight

Civil twilight occurs when the Sun is 6° below the horizon.

common name

Common Names are names other than the catalog designation or catalog cross reference attached to an object. For example, M97 is often called the Owl Nebula.

community

Community is a collection of resources on the Knightware web site for licensed users of Deep-Sky Planner (Desktop and Mobile Editions). These resources include observing plans, equipment lists and software updates (Desktop Edition only).

compatible document

A Compatible Document is a document that contains the same data as another type of document, but shows it in a different way. For example, a darkness text document can contain the same settings as a darkness graphic document, but they appear differently when they are opened and displayed. You can save a document and open it later as a compatible type of document.

concentration class

See Shapley-Sawyer for globular cluster concentration.

See Trumper type for open cluster concentration.

context menu

A context menu is a menu that pops up in response to a right click on a window or control. It contains menu items that affect the window or control to which the context menu is attached.

cross reference

Cross references are alternate names for an object that are taken from the object's catalog.  Some catalogs do not contain any cross references while others contain several per object.  Only cross references to a catalog contained in Deep-Sky Planner's database are included.  For example the PGC catalog contains cross references for PGC 42038 that include NGC 4565, MCG 4-30-6, and UGC 7772.  Cross references to other catalogs are not included (in this case, CGCG 129-10.)

An exception was made for the Revised NGC/IC catalog.  Since IC, M and NGC objects are so commonly observed, cross references to the other catalogs in the database were mined from all of the catalogs.  For example, M 1 appears in the Revised NGC/IC catalog where it is also designated NGC 1952; in addition it appears in the Cederblad's Catalog of Bright Diffuse Galactic Nebulae catalog as Ced 53 and in Greens' Catalogue of Galactic Supernova Remnants as SNR 184.6-05.8

D

darkness zone

darkness zone is a color swatch that represents a range of darkness values as used in The New World Atlas of Artificial Sky Brightness (Falchi et al, 2016). The values are:

Dawe's Limit

    A theoretical estimate of the resolving power of an instrument.  It is expressed in arcseconds.

deep-sky rise and set

Deep-Sky and stellar object rise and set is defined as the apparent time of geometric rise or set of the object (considered to be a point source), taking into account an atmospheric refraction of 0°34' (0°.5667).

desktop

The desktop is the main window of the program. It contains the menu bar (File, Observing Log, Equipment/Observer, Telescope Control, Options, Community, Help), the tool bar (containing speed buttons), the document display area, and the status bar.

document

Deep-sky and star database search settings, and planetary calculation settings are stored in documents. This is similar to the way that a word processor stores the text of a letter in a document. Documents may be exported, printed, opened, changed and saved just as with a word processor.

DSC

DSC, or digital setting circles, is an electronic device that provides a digital read out of the telescope's position by reading optical encoders attached to the axes of the telescope mount.

E

elevated privileges

Windows Vista and later allow a program to run with special elevated privileges to accommodate program functions that use certain services or resources that are restricted by User Account Control (UAC.) You do not need to run with elevated privileges if UAC is turned off.

Running a program with elevated privileges is achieved by right-clicking on a program icon on the Windows desktop, start menu, etc, and selecting Run as Administrator from the context menu. The program runs in this special privileged mode until you close the program.

elongation angle

Elongation angle is the sun - earth - object angle.  It is the angular distance of an object from the sun as viewed from earth.

ephemeris

An ephemeris (plural ephemerides) contains data calculated for a celestial body at a particular instant in time. The data include position, rise, set, and transit time, etc.

equatorial coordinates

equatorial coordinates (right ascension and declination) are given in Deep-Sky Planner as follows:

▪coordinates in deep-sky and stellar documents are geocentric and refered to the the epoch and standard equinox of J2000.0 (J2000)

▪coordinates in ephemeris, asteroid search and comet search documents are apparent topocentric (i.e., corrected for parallax) and are referred to the equinox of the instant of the ephemeris calculation (Now)

▪telescope control panel shows the equinox to which the telescope's equatorial coordinates are referred by the driver (one of J2000, J2050 or Now)

▪coordinates in an observing plan document may be one of J2000, J2050 or Now

event

An Event is a point in time when the position of one solar system body in relation to another is of significant interest, for example, an eclipse or a greatest elongation from the sun.

exit pupil

Exit pupil is the diameter of the light pencil emerging from the eyepiece containing the fully illuminated image. Ideally the exit pupil will not exceed the diameter of the fully dilated eye.

eye pupil

Eye pupil is the diameter of the fully dilated eye. The average eye pupil diameter is 7.0 mm but decreases with age. This diameter can be measured with a pupillometer.

F

favorite location

A favorite location is the location that is selected automatically when a new document is opened, or when new observing sessions are added to the observing log. You can select a different location for any document after it is opened. The favorite location (if there is one selected) is shown in the status bar of the main program window.

favorite observing project

The favorite observing project is the project that is selected automatically when adding, browsing, or searching observations.  Since you are not required to organize observations into projects, this is simply a convenient option. You may select any project in the Observing Log or none when adding, browsing, or searching.

field of view

The field of view (FOV) is the angular dimension, expressed as height x width, of sky that is captured by a combination of a camera's detector (CCD chip or emulsion film frame) and a lens or telescope.  FOV is expressed in degrees or arcminutes.

FOV (deg) = 57.3 * Detector dimension (mm) / EFL(mm)

FOV (arcmin) = FOV (deg) * 60

where EFL (mm) is effective focal length = barlow/compressor magnification * instrument focal length (mm)

font

Font is the style of text used in displaying report windows and in printing documents. True Type fonts are recommended.

G

H

Herald-Bobroff AstroAtlas

Herald, David, and Bobroff, Peter, The Herald-Bobroff AstroAtlas, HB2000, 1994.

Hubble Morphological type

Hubble morphological type is a code that describes the general morphology of galaxies. The type codes present in the database have many extensions that indicate more detailed morphology. The table below indicates the most basic types.

I

image scale

Image scale is the resolution in arcseconds per pixel of a CCD camera and lens or telescope combination.

Image scale (arcsec/pixel) = 57.3 * 3600 * Pixel Size (um) / 1000 * EFL(mm)

where EFL (mm) is effective focal length = barlow/compressor magnification * instrument focal length (mm)

interstellarum Deep Sky Atlas

Stoyan, Ronald, and Schurig, Stephan, interstellarum Deep Sky Atlas, Oculum Verlag GmbH, Erlangen, 2013, 2014.

J

K

L

local horizon model

Local horizon model defines obstructions at your observing location. Both upper and lower obstructions may be included.

Local horizon model affects reports is 2 different ways. First, if a local horizon model is defined for the selected location and the model is 'applied' in a report, the rise and set times are calculated for the local horizon at the location. These are the approximate times at which an object rises above and sets beneath the local horizon model. The second use of a local horizon model occurs with search reports and observing plans. In this case, objects may be included in a report only if they are are above the lower horizon model and beneath the upper one at a specified time.

Thus, applying a local horizon model affects rise & set times in all reports; filtering objects by their sky position in relation to a local horizon model affects whether objects are displayed in reports.

Note that applying or filtering by a local horizon model results in additional calculations so use this feature only when needed.

local hour angle

Local hour angle specifies the angle between the object and the meridian, expressed as hours and minutes East (E) or West (W) of the meridian.

local apparent sidereal time

The time (in UTC) at which the vernal equinox crosses the local meridian

local time

Local Time, or LT, is the time at your location and is corrected for your time zone and daylight saving time. Time zones are necessary to keep the time of day consistent with the earth's rotation.

M

magnification

see working magnification

magnitude

Magnitude value is followed by a code as described below. When both photographic and photoelectric V (visual) appear in a catalog, photographic magnitudes are followed by a "p".

The GCVS and NSV include a code defining the photometric system used to obtain magnitude:

Code for photometric system. The main codes are p (photographic magnitudes) and V (visual, photovisual, or Johnson's V). Several stars from the 68th Name-List have in these positions "1." designating the 1.04 {mu}m band of the system introduced by G.W.Lockwood. The designations u,v,b,y refer to the Stroemgren system. The symbols "Ic" and "Rc" mean magnitudes in Cousins' I system. "g" designates magnitudes in the system of Thuan and Gunn; "T" stands for broad-band Tycho magnitudes formed from B and V measurements; "r" are red magnitudes not tied to a particular system. An asterisk in the corresponding position means a measurement in white light.
 - N.N. Samus [Moscow Inst. Astron.], Francois Ochsenbein [CDS] 18-Jan-2009, B/gcvs General Catalogue of Variable Stars.
 

Millennium Star Atlas

Sinnott, Roger, and Perryman, Michael A.C., Millennium Star Atlas, Sky Publishing Corporation, 1997.

monitor

Monitor resolution and size determine how much screen area is available to the program. If you increase your monitor resolution, you can fit wider and taller windows on your screen. If your system supports only SVGA resolution (800x600), it is the least resolution supported by Deep-Sky Planner.  The higher the resolution, the more information Deep-Sky Planner can display.

moon rise and set

Moon rise and set are defined as the time of the apparent rise or set of the limb of the moon, taking into account an atmospheric refraction of 0°34' (0°.5667) and a correction factor that varies according to the distance of the moon from the earth.

Morgan-Keenan spectral type

See spectral type.

N

nautical twilight

Nautical twilight occurs when the Sun is 12° below the horizon.

O

object name

Non-numeric object designations (object names) have the following format:

object type

Deep-Sky Planner supports the following types of objects:

observation

An observation is a collection of several related bits of information that together record the name of the object you observed and when, the location from which you observed, the equipment that you used to make the observation, and your personal notes about observing the object.

observing log

The Observing Log holds records of your observations.  Several tools within Deep-Sky Planner allow you to organize, search and report on your observations, as well as import and export them.

observing project

An observing project is simply a way to organize observations.  It holds references to your observations, not the observations themselves so that when a project is deleted, the observation remains in your observing log.  This is like placing a photocopy of your observation notes into a notebook rather than the original copy itself.  This also allows a given observation to appear in several projects if needed.

opacity

Opacity is a relative value used in catalogs of dark nebulae to describe the degree of darkness. The codes are:

P

pane

A pane within a document window is a resizeable window. The top pane contains various date such as the document's search or calculation settings; the bottom pane contains a report.  The panes may be resized by clicking and dragging the raised splitter bar between the panes. The normal cursor changes to the resize cursor when it hovers over the splitter bar.

The splitter bar has a small 'hotzone' button - either or on it indicating that the pane can be popped closed or back to its original position. For example the screenshots below show a deep-sky report with the hotzone button on the splitter bar between the report pane and the filters pane, and between the report pane and the details pane.

A single click of the hotzone button pops the report pane open (below) to reveal as much of the report as possible. A subsequent click pops the upper pane to its original position (above).

phase

Phase is the percentage of a object that is illuminated.

phase angle

Phase angle is the sun - object - earth angle.  It is the angle of illumination of an object as viewed from earth.

planet rise and set

Planet rise and set is defined as the apparent time of geometric rise or set of the center of the planet, taking into account an atmospheric refraction of 0°34' (0°.5667). If a local horizon model is applied, rise and set are the approximate time that the center of the planet rises above or sets below the model.

Pocket Sky Atlas

Sinnott, Roger W., Pocket Sky Atlas, Sky Publishing Corporation, 2006.

position angle

Position angle is the angle from the brighter star to the dimmer star, measured eastwards from north. It is also the angle of the major axis of a galaxy measured eastwards from north.

precession

Precession is the wobbling motion of the earth's rotational axis around the pole of the ecliptic. It takes 26,000 years to make one full rotation. As a result, the vernal equinox moves about 50 arc seconds each year. This causes the equatorial coordinates of deep-sky objects to change slowly with time. All equatorial coordinates in Deep-Sky Planner are precessed to epoch and mean equinox of J2000.0 so that their positions agree with those plotted in Millennium Star Atlas, Sky Atlas 2000.0, and Uranometria 2000.0.

Q

R

S

Shapley-Sawyer concentration class

Shapley-Sawyer concentration class describes the degree of concentration of globular clusters using Roman numerals I through XII, where I is the most concentrated and XII is the least. The system was developer by Harlow Shapley and Helen Sawyer Hogg.

separation angle

Separation angle is the angular distance between double or multiple stars.

session

An observing session defines when and where you made observations, along with optional information about sky conditions and a brief description.

Sky Atlas 2000.0

Tirion, Wil, Sky Atlas 2000.0, Sky Publishing Corporation, 1981.

spectral types

Stars are classified by their spectral type in the Morgan-Keenan system. The following spectral types are available:

The author would like to acknowledge Alan MacRobert's fine article "The Spectral Types of Stars" available from the Sky & Telescope web site, and the serialized articles taken from James B. Kaler's "Stars and Their Spectra" that appeared in Sky & Telescope magazine from February 1986 to May 1988. These provided background material for the lesser known spectral types.

speed button

A speed button is a graphical button that resides on the tool bar. Clicking it causes a program function to occur (as opposed to invoking the program function via the menu.) A tip describing the speed button function is displayed if you move the mouse cursor over a speed button and leave it for a few seconds.

status bar

The status bar is the area at the bottom of the desktop that shows active observing project, favorite location and system date and time. The date and time are shown in the format set in Data Formatting Properties. The status bar also shows hint text for menu items.

stylesheet

A stylesheet is used to customize the layout, colors and fonts for data files and reports.

sun rise and set

Sun rise and set are defined as the apparent rise or set of the limb of the sun, taking into account an atmospheric refraction of 0°34' (0°.5667).

T

tool bar

Tool bar is a collection of speed buttons that "speed" you to a program function. The tool bar can be arranged horizontally at the top or bottom of the desktop window.

transit time

Transit time occurs when an object crosses the observer's meridian. This is also the time at which an object reaches maximum altitude at the observer's location, and the time half way between rise and set.

true field

True field of view is the angular diameter of sky actually visible through an instrument + eyepiece + barlow/compressor combination.  It is computed to be:

TF = eyepiece apparent field / working magnification

Trumpler Type

Trumpler type (Robert Trumpler) describes the concentration, brightness and richness of an open cluster.

U

universal time

Universal Time, or UT, is the civil time at the Greenwich meridian. Astronomers use UT to express times to avoid any confusion associated with an observer's time zone. UT is usually expressed in 24 hour format, so that 13:00 UT is known to be 1 pm civil time on the Greenwich meridian.

Uranometria 2000.0

Tirion, Wil, Rappaport, Barry, and Lovi, George, Uranometria 2000.0, Willmann-Bell, Inc, 1987.

Uranometria 2000.0 2d Ed

Tirion, Wil, Rappaport, Barry, and Remaklus, Will, Uranometria 2000.0, Willmann-Bell, Inc, 2001.

V

variable star epoch

Variable star epochs are stated in Julian days for minimum light for all eclipsing and ellipsoidal variables, as well as for RV Tau and RS CVn types, and for maximum light for all other types. For well-studied Miras (M) and some semi regulars (SRa-d), the catalog usually gives one of the most recent epochs of maximum light. Epochs for novae (types N) and supernovae (types SN) are given in Julian days followed by a year of outburst enclosed in parentheses.

The following codes are also possible:

:  epoch is uncertain;
 + epoch may be later than that reported;
 -  epoch may be earlier than that reported.

variable star magnitudes

Variable star magnitudes are given to tenths, except photoelectric magnitudes given originally to hundredths are rounded to tenths. P indicates photographic magnitude, V indicates visual, photo visual, or UBV.

variable star periods

Variable star periods are stated in days with varying accuracy. For well-studied Miras and some semi regulars having reasonably constant periodicities, mean values of the periods for the entire observed intervals are usually reported, since they may be considered as the most probable values for predicting future epochs. Formal (double) periods are usually reported for RV Tau stars and fundamental periods for semi regulars. For U Gem and recurrent novae, the mean cycle values are given if known.

The following codes are also possible:

:   period is uncertain
 N  actual period unknown; the value given is a time interval between two maxima (or minima) separated by an unknown number of cycles

version

Version defines a build identifier for the Deep-Sky Planner application. It looks like M.m.r.b where M is the major version, m is the minor version, r is the release version and b is the build number. For Deep-Sky Planner, the major version (like 9.0.0.0) defines the original publication of a series of the product. The minor version defines the release of new features in the major version series. The release version varies as bugs are fixed. The build number is usually 0; other values apply to test builds and are not released to the public.

W

working magnification

the working magnification of an instrument + eyepiece + barlow/compressor combination is computed to be:

working mag = barlow/compressor mag * instrument focal length / eyepiece focal length

X

Y

Z

Help file version 9.2.3.0 ▪ Copyright © 2024-2026 Knightware, LLC

Help file version: 9.2.3.0 ▪ Copyright © 2026 Knightware, LLC