European Southern Observatory New Technology Telescope

General :
Observations :

Near-Infrared Background

Dark Time

The background level in the near-infrared is a highly variable function of time and of the methereological conditions. During dark time we have measured the following values for the sky brighteness at the zenith

Bright Time

The effect of the moon is less important in the IR than it is in the visible. The sky brighteness at the zenith during full moon can increase by about 1 mag in J and H while it remains about the same in K with respect to the dark time values. Of course the sky brighteness during bright time is a function of the moon distance. We have measured this effect during full moon. In the following figure we plot the sky brighteness as function of the moon distance. The blue, green and red curves correspond to the J, H and Ks filters respectively. The background can be considered almost constant for moon distances larger than 20 deg in J and H, and larger than10 deg in Ks. For this reason it is advisable to observe at moon distances larger than these. Below these values the background has a very steep gradient, note that the scale of the plot is logarithmic.

Send comments to: NTT Webmasters <nttweb@www.ls.eso.org> Last Update: March 24, 2002 (Leo Vanzi)