Humankind has long marvelled at the Sun and basked in its warmth. So it may be disconcerting to learn that the Sun is not quite as bright as we thought — it now seems that our star gives off 0.34% less radiation than was previously estimated (G. Kopp and J. L. Lean Geophys. Res. Lett. 38, L01706; 2011).

Total solar irradiance, a measure of the Sun's cumulative energy output, is a fundamental, if little-appreciated, number in Earth science. It acts as a baseline for our calculations on climate, and accounts for almost half of our planet's energy balance with impressive simplicity. (It is on the other half of the equation, concerning what happens to that energy once it enters the system, that things get complicated.) The new value should not make calculations trickier: equations representing clouds, for instance, come with enough uncertainty to absorb the effect. But it is important to have an accurate picture of the Sun's output.

Measurements of the Sun from space began in November 1978, and the subsequent continuous record has proved invaluable to the study of solar cycles and the impact of solar variation on the climate system. Next month, NASA will launch the Glory spacecraft to bolster and extend that record over the coming years (see page 457).

Glory's measurements of the Sun could be the most accurate so far, and they should be the first to match earlier measurements — from NASA's Solar Radiation and Climate Experiment — without adjustment. Indeed, solar researchers are now working to calibrate their systems against an absolute standard before launch, which would make it easier to work with different instrument designs.

The solar physicists who are doing this work have two fears. The first is that the continuous record of solar irradiance measurements will one day come to an end. With the Swiss sensor PREMOS in the air — launched last June on the French satellite PICARD — and Glory on the way, the outlook is bright over the next few years. But so far, only the United States has proposed a follow-on mission, scheduled for 2014.

Physicists' second fear boils down to a moral hazard. Part of the rationale behind the search for an absolute standard is to make the data record resilient enough to withstand future gaps in measurement. But if funders know that the technology has improved to that point, why should they approve missions to plug the gaps? We are not there yet; instrument-makers have yet to prove that their toys are as precise, robust and predictable as they claim. But a future where these crucial data are accurate enough to stand on their own, independently of the data record, should be pursued, not feared.