Generate a selection from a catalogue
Arbitrary expression: objects which satisfy an algebraic expression which you supply.
Range within a sorted column: objects which lie within a given range for a specified column. This option only works on sorted columns. However, because it is not necessary to read the entire column it works essentially instantaneously, irrespective of the number of rows in the catalogue.
Rectangular area: objects which lie within a given rectangle. (If the columns are spherical-polar coordinates, such as Right Ascension and Declination, rather than Cartesian coordinates then the sides of the rectangle become parallels and great circles.)
Circular area: objects which lie within a given angular distance from a specified point. This type of selection is only likely to be used on columns of celestial coordinates.
Polygonal area: objects which lie inside (or outside) a given polygon.
Every Nth entry: every Nth object from the catalogue. This option is useful for producing a smaller, but representative, sample of a large catalogue. Such a sample might then be investigated interactively in cases where the original catalogue was too large to be studied interactively.
If the column within which the range is being specified is not an angle then simply enter the required value.
If the column is an angle then the value can be entered as either a decimal value in radians or a sexagesimal value in hours or degrees, minutes and seconds. If a sexagesimal value is specified then the hours or degrees, minutes and seconds should be separated by a colon (’:’). Optionally fractional seconds can be specified by including a decimal point and the required number of places of decimals. An unsigned value is assumed to be in hours and a signed value in degrees (a negative angle cannot be specified in hours). That is, a positive angle in degrees must be preceded by a plus sign.
Examples: any of the following values could be entered to to specify an angle of 30 degrees:
2:00:00.0 hours (decimal point included in seconds) 2:00:00 hours (integer number of seconds)
$+$30:00:00.0 degrees (decimal point included in seconds) $+$30:00:00 degrees (integer number of seconds)
0.5235988 radians
If the column within which the range is being specified is not an angle then simply enter the required value.
If the column is an angle then the value can be entered as either a decimal value in radians or a sexagesimal value in hours or degrees, minutes and seconds. If a sexagesimal value is specified then the hours or degrees, minutes and seconds should be separated by a colon (’:’). Optionally fractional seconds can be specified by including a decimal point and the required number of places of decimals. An unsigned value is assumed to be in hours and a signed value in degrees (a negative angle cannot be specified in hours). That is, a positive angle in degrees must be preceded by a plus sign.
Examples: any of the following values could be entered to to specify an angle of 30 degrees:
2:00:00.0 hours (decimal point included in seconds) 2:00:00 hours (integer number of seconds)
$+$30:00:00.0 degrees (decimal point included in seconds) $+$30:00:00 degrees (integer number of seconds)
0.5235988 radians
If the X column within which the minimum is being specified is not an angle then simply enter the required value.
If the column is an angle then the value can be entered as either a decimal value in radians or a sexagesimal value in hours or degrees, minutes and seconds. If a sexagesimal value is specified then the hours or degrees, minutes and seconds should be separated by a colon (’:’). Optionally fractional seconds can be specified by including a decimal point and the required number of places of decimals. An unsigned value is assumed to be in hours and a signed value in degrees (a negative angle cannot be specified in hours). That is, a positive angle in degrees must be preceded by a plus sign.
Examples: any of the following values could be entered to to specify an angle of 30 degrees:
2:00:00.0 hours (decimal point included in seconds) 2:00:00 hours (integer number of seconds)
$+$30:00:00.0 degrees (decimal point included in seconds) $+$30:00:00 degrees (integer number of seconds)
0.5235988 radians
If the X column within which the maximum is being specified is not an angle then simply enter the required value.
If the column is an angle then the value can be entered as either a decimal value in radians or a sexagesimal value in hours or degrees, minutes and seconds. If a sexagesimal value is specified then the hours or degrees, minutes and seconds should be separated by a colon (’:’). Optionally fractional seconds can be specified by including a decimal point and the required number of places of decimals. An unsigned value is assumed to be in hours and a signed value in degrees (a negative angle cannot be specified in hours). That is, a positive angle in degrees must be preceded by a plus sign.
Examples: any of the following values could be entered to to specify an angle of 30 degrees:
2:00:00.0 hours (decimal point included in seconds) 2:00:00 hours (integer number of seconds)
$+$30:00:00.0 degrees (decimal point included in seconds) $+$30:00:00 degrees (integer number of seconds)
0.5235988 radians
If the Y column within which the minimum is being specified is not an angle then simply enter the required value.
If the column is an angle then the value can be entered as either a decimal value in radians or a sexagesimal value in hours or degrees, minutes and seconds. If a sexagesimal value is specified then the hours or degrees, minutes and seconds should be separated by a colon (’:’). Optionally fractional seconds can be specified by including a decimal point and the required number of places of decimals. An unsigned value is assumed to be in hours and a signed value in degrees (a negative angle cannot be specified in hours). That is, a positive angle in degrees must be preceded by a plus sign.
Examples: any of the following values could be entered to to specify an angle of 30 degrees:
2:00:00.0 hours (decimal point included in seconds) 2:00:00 hours (integer number of seconds)
$+$30:00:00.0 degrees (decimal point included in seconds) $+$30:00:00 degrees (integer number of seconds)
0.5235988 radians
If the Y column within which the minimum is being specified is not an angle then simply enter the required value.
If the column is an angle then the value can be entered as either a decimal value in radians or a sexagesimal value in hours or degrees, minutes and seconds. If a sexagesimal value is specified then the hours or degrees, minutes and seconds should be separated by a colon (’:’). Optionally fractional seconds can be specified by including a decimal point and the required number of places of decimals. An unsigned value is assumed to be in hours and a signed value in degrees (a negative angle cannot be specified in hours). That is, a positive angle in degrees must be preceded by a plus sign.
Examples: any of the following values could be entered to to specify an angle of 30 degrees:
2:00:00.0 hours (decimal point included in seconds) 2:00:00 hours (integer number of seconds)
$+$30:00:00.0 degrees (decimal point included in seconds) $+$30:00:00 degrees (integer number of seconds)
0.5235988 radians
The value may be specified as either a sexagesimal value in hours or a decimal value in radians. If the value is supplied as sexagesimal hours then the hours, minutes and seconds must be separated by a colon (’:’). Optionally fractional seconds can be specified by including a decimal point and the required number of places of decimals. A negative angle may be specified by preceding the value by a minus sign.
Examples: an angle of 10 hours, 30 minutes and 15.3 seconds may be specified by entering either of the following two values:
10:30:15.3 sexagesimal hours 2.7500062 radians
The value may be specified as either a sexagesimal value in degrees or a decimal value in radians. If the value is supplied as sexagesimal degrees then the degrees, minutes and seconds must be separated by a colon (’:’). Optionally fractional seconds can be specified by including a decimal point and the required number of places of decimals. A negative angle may be specified by preceding the value by a minus sign.
Examples: a negative angle of 33 degrees, 30 minutes and 15.2 seconds may be specified by entering either of the following two values:
33:30:15.2 sexagesimal degrees
0.584759 radians
The value may be specified as either a sexagesimal value in minutes and seconds of arc or a decimal value in radians. If a sexagesimal value is supplied then the minutes and seconds of arc must be separated by a colon (’:’). Note that a colon must be present if the value is to interpretted as minutes of arc; if no colon is present it will be interpretted as radians. Optionally fractional seconds can be specified by including a decimal point and the required number of places of decimals. A negative angle may be specified by preceding the value by a minus sign.
Examples: a radius of two minutes of arc may be specified by entering either of the following two values:
2:0 sexagesimal minutes of arc 5.8178E-4 radians
The equinox is specified as a time system followed by the value in that system in years. A single alphabetical character is used to identify each of the two time systems supported: B for Bessellian and J for Julian. Optionally decimal fractions of a year may be specified by including a decimal point followed by the required fraction.
Examples: J2000 Julian equinox 2000. B1950 Bessellian equinox 1950.
The epoch is specified as a time system followed by the value in that system in years. A single alphabetical character is used to identify each of the two time systems supported: B for Bessellian and J for Julian. Optionally decimal fractions of a year may be specified by including a decimal point followed by the required fraction.
Examples: J1996.894 Julian epoch of 1996.894. B1955.439 Bessellian epoch of 1955.439.
A positive value corresponds to an object which is red-shifted or receding and a negative value to one which is blue-shifted or approaching.