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Calculate Airmass
The Calculate Airmass command opens a
worksheet dialog where you can calculate an airmass value or a
range of values. The calculation of a single airmass value requires
the 6 quantities shown in the left left hand column of the window
below. To calculate a range of airmass and list or plot the result,
enter values into the right hand column and select the appropriate
options. For a description of input formats, see the section
Data Formats, below.
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Properties for Airmass Calculation
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Right Ascension
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The right ascension coordinate in units of "hh mm
ss" for hours, minutes, and seconds of time. The seconds value may
include decimal digits.
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Declination
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The declination coordinate in units of "dd mm ss"
for degrees, minutes, and seconds of angle. The degrees value may
be negative and the seconds value may include decimal digits.
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Site Longitude
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The longitude of the observing site in units of
"dd mm ss" for degrees, minutes, and seconds of angle. The degrees
value may be negative and the seconds value may include decimal
digits.
NOTE: The longitude is negative west of the Prime
Meridian at Greenwich, England (e.g., the Americas), as per the
World Geodetic System specification WGS84.
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Site Latitude
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The latitude of the observing site in units of "dd
mm ss" for degrees, minutes, and seconds of angle. The degrees
value may be negative and the seconds value may include decimal
digits.
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UT Date
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The UT date of observation in units of "yyyy mm
dd" for year, month, and day. The year requires 4 digits but the
month and day may each use 1 or 2 digits. When the  Enable Range
option is used, this becomes the starting date for the range.
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UT Time
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The UT time of observation in units of "hh mm ss"
for hours, minutes and seconds. Each value may use 1 or 2 digits.
When the Enable
Range option is used, this becomes the starting time for the
range.
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Click this button to calculate a single value of
airmass using values in the left hand column. Values in the right
hand column under Enable
Range are ignored for this calculation.
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Airmass
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The airmass based on all entries in the left hand
column of text fields.
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Options in the right hand column are used to list
or plot a range of airmass.
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Enable Range
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Check this box to activate the right hand column
of text fields for computing a table or graph of airmass over a
range of time.
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End Data & Time
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This group controls the calculation of a range of
airmass between the UT date and time in the right and left
columns.
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[List]
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Click this button to list the airmass at 10 minute
intervals in the range of UT Date and UT Time.
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[Plot]
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Click this button to plot the airmass in the range
of UT Date and UT Time.
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Plot JD Fraction
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Check this box to subtract the integral part of
the JD value at the UT Date and UT Time at the beginning of the
range.
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Max Airmass
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Enter the maximum value of airmass to be listed
and plotted. Usually a value of 3 to 5 is practical.
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UT Date (right column)
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The Ending UT date of observation in units of
"yyyy mm dd" for year, month, and day. The year requires 4 digits
but the month and day may each use 1 or 2 digits.
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UT Time (right column)
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The ending UT time of observation in units of "hh
mm ss" for hours, minutes and seconds. Each value may use 1 or 2
digits.
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Data Formats
The date, time, latitude, and longitude fields
accept multiple values in the form of (Year, Month, Day), (Hours,
Minutes, Seconds), and (Degrees, Minutes, Seconds), abbreviated as
yyyy mm dd, hh mm ss, and dd mm ss, respectively. Mira tolerates a
variety of delimiters between the numbers in each field. All the
accepted delimiters are listed in the table below. The window shown
above uses spaces between the numbers, which is listed as (space)
in the table below. You can also use several symbols such as / and
the letters h, m, d, etc. to separate values in the field. Choose a
delimiter that works for you because it is easy to type or makes
the entry easy to understand.
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Field delimiters
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hh mm ss
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(space) / : – , " ' H h M m S s
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dd mm ss
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(space) / : – , " ' D d M m S s
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yyyy mm dd
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(space) / : – , " ' Y y M m D d (degree sign)
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Listing and Plotting a Range of Airmass
The [List] and [Plot] buttons use ending values of date and
time in the right hand column to list and plot the range of airmass
over time. Using the settings shown in the window above, the
airmass was tabulated (listed) and plotted over the period 03h UT
on June 1 through 10h UT on June 2 (a range of 1 day 7 hours). The
following pictures show the results in a
Text Window and
Plot Window. Note that the Plot Window shows
the result of using the Plot JD Fraction option
which subtracts the integral part of the starting JD Value from the
data and lists it in the X-Axis Label.
Related Topics
Calculate Image Scale
Photometry Keywords
Mira Pro x64 User's Guide, Copyright Ⓒ 2023 Mirametrics, Inc. All
Rights Reserved.
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