What is an ACRIM anyway?
The Active Cavity Radiometer Irradiance Monitor (ACRIM) is a instrument designed to fly in space and measure the total solar irradiance (the total light energy from the sun). It is a radiometer because radiometers are instruments that interact with light. It is an irradiance monitor because it measures light for a long period of time. It monitors sun light. The words Active Cavity describe the fact that the active cavity radiometer actively maintains the temperature of its solar sensing cavity slightly hotter than the rest of the instrument at all times using an automatic electronic servosystem. It is Active.

What does ACRIM measure?
ACRIM measures the total energy of the light that comes from the sun.

Why do we make this measurement?
If we know the total amount of energy that the sun delivers to the earth, then we can build scientific models of the earth's climate system. The energy from the sun is the key energy input into this system.

What does the ACRIM data look like?

This chart shows the daily average of total solar irradiance (TSI) for the ACRIM I and ACRIM II experiments. ACRIM I flew on the Solar Maximum Mission (SMM) spacecraft from 1980 to 1989. ACRIM II flew on the Upper Atmosphere Research Satellite (UARS) from 1991 to the present. Each point on the curve is the daily average of the total solar irradiance measurements taken by ACRIM on the given day. The vertical axis is shown in watts per meter squared (the amount of energy that hits a given surface at a certain time). The horizontal axis is time shown in days.