Jodrell Bank Centre for Astrophysics

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Supplementary notes to the Jodrell Bank - Live! pages

UTC

This is the Universal Time of last received update from that particular telescope. The Universal Time is roughly equivalent to the Greenwich Mean Time. If the status of a given telescope has not been updated recently, then its "update UTC" will be displayed in red, flashing or both.
 

Telescope

This is the name of the telescope or antenna, whose status is shown in that particular column. Jodrell Bank Observatoryoperates nine different radiotelescopes, eight of which are shown on the Jodrell Bank Live!page. The one that isn't shown is the experimental 7m antenna, which is used for graduate projects, equipment tests and other experiments. Of the eight telescopes displayed, the Lovell, Mark II and 42ft telescopes are located at the Jodrell Bank site. The rest are scattered across the United Kingdom.
 

Diameter

This is the diameter of the dish of the telescope, expressed in meters. The Mark II telescope is somewhat unusual, in that it has an elliptical dish. Therefore it's diameter is expressed as the horizontal and vertical diameters, respectively.
 

ActAz

This is the actual azimuth of the telescope. For an explanation of azimuth, see the Azentry.
 

ActEl

This is the actual elevation of the telescope. For an explanation of elevation, see the Elentry.
 

DemAz

This is the demanded azimuth of the telescope. When the telescope is requested to go to a new position in the sky, it is given a demanded azimuth and elevation (for a description of azimuth and elevation, see Azand El, respectively). The control system knows the difference between the demanded and actual positions and controls the telescope motors to try to make the actual value match the demanded one.
 

DemEl

This is the demanded elevation of the telescope. When the telescope is requested to go to a new position in the sky, it is given a demanded azimuth and elevation (for a description of azimuth and elevation, see Azand El, respectively). The control system knows the difference between the demanded and actual positions and controls the telescope motors to try to make the actual value match the demanded one.
 

DemLong

This is the demanded longitude of the telescope. Like DemAz, it is request for a given position in the sky, which the antenna control system will try to achieve. However, it is more general than DemAzas it can refer to either Azimuth or Right Ascension depending on what the Coordinate modeis set to.
 

DemLat

This is the demanded latitude of the telescope. Like DemEl, it is request for a given position in the sky, which the antenna control system will try to achieve. However, it is more general than DemElas it can refer to either Elevation or Declination depending on what the Coordinate modeis set to.
 

Az

This is the demanded azimuth of the telescope. This field will only be filled if the Coordinate modeis set to Az/El. If this is the case, the Azimuth shown will match the DemAzvalue. Azimuth is a measure of how far round from North that telescope has rotated, i.e. it is the compass bearing. It is measured in degrees, so that North is 0 degrees, East is 90, South is 180 and West is 270.
 

El

This is the demanded elevation of the telescope. This field will only be filled if the Coordinate modeis set to Az/El. If this is the case, the Elevation shown will match the DemElvalue. Elevation is a measure of how far up the telescope is pointing. It is measured in degrees and the horizon is defined as 0 degrees and straight up is defined as 90. Elevation is sometimes called altitude, but this is more commonly used to describe the height in metres above sea-level.
 

RA

This is the demanded Right Ascension (RA) of the telescope. This field will only be filled if the Coordinate modeis set to B1950or J2000. Right Ascension is equivalent to longitude on the celestial sphere (rather than the Earth). It is measured in hours, minutes and seconds, where there are 60 seconds in a minute and 60 minutes in an hour, just like time. There are 24 hours in a revolution, therefore 1 hour of RA at the celestial equator is equivalent to 15 degrees. An interesting point to note is that the local sidereal time (LST) is the Right Ascension of the zenith (the point directly overhead).
 

Dec

This is the demanded Declination (Dec) of the telescope. This field will only be filled if the Coordinate modeis set to B1950or J2000. Declination is the equivalent of celestial latitude and is measured in degrees, arcminutes and arcseconds. There are 60 arcseconds to and arcminute and 60 arcminutes to a degree. Declination ranges from +90 degrees (the North Celestial Pole) to -90 degrees (the South Celestial Pole). The declination of the zenith (the point in the sky directly overhead) is equal to the latitude on the Earth of the observer.
 

Coordinate mode, Epoch

This is the coordinate system for the demanded coordinates for a given telescope. When asking a telescope to go to a certain position in the sky, there are numerous ways of specifying that point.

• AZ/El- This indicates that the requested coordinates are specified as an Azimuth and Elevation (see Azand El).
• B1950- (see J2000).
• J2000- This indicates that the requested coordinates are specified as equatorial coordinates - i.e. Right Ascension and Declination (see RAand Dec). The B1950 or J2000 itself stands for the epoch of the reference frame.

 

AzOff

This is the offset applied to the azimuth.
 

ElOff

This is the offset applied to the elevation.
 

LO1, LO2, LO3, LO4, ...

These are the frequency values for the various local oscillators (LOs) in the given telescope. The values are usually expressed in MHz (megahertz or millions of cycles per second). The LOs are used to convert high frequency radio signals to lower frequency intermediate signals. The lower frequency signals are easier to process and require less complicated electronics.
 

Tsys

Tsys (or system temperature) is a measure of how sensitive the receiver system is on a particular telescope. It is measured in kelvin (0 K indicates a "perfect" receiver).
 

Motors

Each telescope has an azimuth and elevation motor. Whether these motors are on or off is shown in this field, for each telescope. The first flag is for azimuth and the second is for elevation.
 

Control

This indicates which terminal or computer has control of the telescope at that particular time.
 

Cryostat Pressure

All the MERLIN telescopes and the Lovell telescope have cooled receivers to improve their sensitivity. This reading shows the pressure in bars of the liquid helium used as a refrigerant.
 

Cryostat Temperature

All the MERLIN telescopes and the Lovell telescope have cooled receivers to improve their sensitivity. This reading shows the temperature in degrees Kelvin of the liquid helium used as a refrigerant.