Wide-field Infrared Survey Explorer


When will WISE observe a source?

WISE will generally be observing a semi-circle at an ecliptic longitude 95o larger than the ecliptic longitude of the Sun (blue curve below), and another semi-circle at an ecliptic longitude 90o smaller than the ecliptic longitude of the Sun (red curve below). The asymmetry allows WISE to recover from a brief safing event by decreasing the ecliptic longitude of the scan circles by 1o per day of duration for the safing event. This does not cause WISE to scan any closer to the Sun.


The graph above shows the actual ecliptic longitude of the scan semi-circles as a function of day of 2010, for a nominal survey plan. There are small toggles on every other orbit to smooth out the influence of the South Atlantic Anomaly, and a monthly sawtooth designed to get data before or after the Moon crosses the scan circle. While WISE plans to never look at the Moon, we will collect and throw data with the Moon closer than 15o to the line-of-sight. The monthly sawtooth motion covers these Moon affected regions twice so the WISE catalog will not have holes caused by the Moon.

The yellow region shows the actual survey interval, from 1 month after the 7 Dec 2009 launch date to 10 months after launch.

It should be possible to predict the dates a source will be observed by computing its ecliptic longitude, adding a ±0.4o/cos(latitude) range, and then finding the date(s) when the above curves are in the source's ecliptic longitude range. This gives the best estimate available until we know the orbit after launch, but remember that safing events could delay the survey by up to 5 days.

Last modified 26 Sep 2009