cxotime

Time class for Chandra analysis that is based on astropy.time.Time.

The CXO-specific time formats are shown in the table below. The CxoTime class default is to interpret any numerical values as secs (aka cxcsec in the native Time class).

All of these formats use the UTC scale.

Format	Description
secs	Seconds since 1998-01-01T00:00:00 (tt)
date	YYYY:DDD:hh:mm:ss.ss..
greta	YYYYDDD.hhmmsssss
maude	YYYYDDDhhmmsssss
frac_year	YYYY.fffff

Important differences:

• In CxoTime the date '2000:001' is '2000:001:00:00:00' instead of '2000:001:12:00:00' in DateTime (prior to version 4.0). In most cases this interpretation is more rational and expected.

• In CxoTime the date '2001-01-01T00:00:00' is UTC by default, while in DateTime that is interpreted as TT by default. This is triggered by the T in the middle. A date like '2001-01-01 00:00:00' defaults to UTC in both CxoTime and DateTime.

• In CxoTime the difference of two dates is a TimeDelta object which is transformable to any time units. In DateTime the difference of two dates is a floating point value in days.

• Conversely, starting with CxoTime one can add or subtract a TimeDelta or any astropy Quantity with time units.

The standard built-in Time formats that are available in CxoTime are:

Format	Example
byear	1950.0
byear_str	'B1950.0'
cxcsec	63072064.184
datetime	datetime(2000, 1, 2, 12, 0, 0)
decimalyear	2000.45
fits	'2000-01-01T00:00:00.000(TAI)'
gps	630720013.0
iso	'2000-01-01 00:00:00.000'
isot	'2000-01-01T00:00:00.000'
jd	2451544.5
jyear	2000.0
jyear_str	'J2000.0'
mjd	51544.0
plot_date	730120.0003703703
unix	946684800.0
yday	2000:001:00:00:00.000