Developers guide

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E.2.5. Dynamical time
Dynamical Time, introduced in 1984 as a replacement for ephemeris time, more accurately
defines a uniform astronomical time scale.
Terrestrial Dynamical Time (TDT) is a time scale tied to the earth, whereas Barycentric Dynamical
Time (TDB) is used as a time reference for the barycentre
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of the solar system. When the
difference of these two values (less than a few milliseconds) is considered negligible, TDT is simply
referred to as TT. In most cases, TDT is considered to be equal to TAI plus 32.184 seconds.
E.2.6. Julian dates
The Julian Day Number (JDN) is a count of days elapsed since Greenwich mean noon on 1
January 4713 B.C., Julian proleptic calendar. The Julian Date (JD) is the Julian day number
followed by the fraction of the day elapsed since the preceding noon.
The Modified Julian Date (MJD) is calculated as MJD = JD - 2400000.5. The 0.5 is included so that
midnight, rather than noon, defines the change over point from one day to the next. MJD 0
started at 0000h GMT on Wednesday 17 Nov 1858 AD.
E.3. Gamma ray bursts
Gamma Ray Bursts (GRB’s) are spectacular explosions of energy originating from distant galaxies.
Lasting from 10 milliseconds to more than 15 minutes, these explosions release as much energy in
10 seconds, as a billion of our Suns. Despite the fact that GRB’s occur quite frequently,
approximately daily, very little is known of their nature or origin.
They were first discovered accidentally in the late 1960’s by a team of American scientists
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commissioned by the military to monitor Soviet nuclear activity. Since then scientists have had
difficulty studying them due to their short life span. The Gamma Ray Coordinate Network (GCN)
was established to process incoming GRB data from satellites and coordinate observing.
The GCN is connected to a large network of satellites and spacecraft capable of detecting
GRB’s. When a GRB is detected, its RA and Dec is calculated and then broadcast to GCN
subscribers within seconds, allowing remote observatories to obtain data while the GRB is still
active.
The APT is ideal for observing the GRB’s due to its wide field of view and fully automated
operation.
E.4. Astronomical filters
Astronomical filters are special types of tinted lenses placed in front of the CCD to enhance the
images acquired. Each filter only allows light from a limited range of wavelengths to pass
through it. Astronomers exploit this behaviour to mask out specific parts of the spectrum, thus
enhancing the image.
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These errors were first discovered in the 1930’s
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Centre of mass, similar to centre of gravity
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led by Ray Klebesadel