Solar flares are explosive events that last not too long, so actually, your bigger problem will be to be able to see them when they are happening.

Normally they are classified by their X-ray flux, and they can be either X, M, C, B or A class which corresponds to the logarithmic scale of $Watts/m^2$ ($10^{-4}, 10^{-5}, 10^{-6}, 10^{-7}, 10^{-8}$ respectively). You can understand better what I mean by looking at the real time lightcurves obtained from GOES satellite

These peaks have different duration depending of the flare, there are some records of flares lasting few hours where the shortest can be shorter than a minute.

All the above applies to X-ray flares, which we cannot seen from Earth, we need to put some instrument on board spacecraft or rocket so we go above the part of the atmosphere that absorbs them.

Now, if you want to see them by using an optical telescope you have two options, either using the whole visible range by projection or through an Hydrogen alpha filter. In this case the flare classification is different than in the X-ray case. Where the flare class in X-ray is measured by the enhanced of flux produced, the optical class is based by the area it covers. The Solar Influence Data Analysis Center offers a table with their properties and the corresponding X-ray flare type:

| Area (sq deg) |Area (10^{-6} solar A)|Class | Typical corresponding SXR Class| |-----------|-----------------|------:|------------------------ | <= 2.0 | <= 200 | S | C2 | | 2.1-5.1 | 200-500 | 1 | M3 | | 5.2-12.4 | 500-1200 | 2 | X1 | | 12.5-24.7 | 1200-2400 | 3 | X5 | | >24.7 | > 2400 | 4 | X9 |

For example, the famous Carrington's event (Sept. 1, 1859) was observed and hand-drawn from Carrington by projection. But, as this article says: "He was lucky enough to be in the right place at the right time..." you need too to be quite lucky to observe one of these.

Solar flares are explosive events that last not too long, so actually, your bigger problem will be to be able to see them when they are happening.

Normally they are classified by their X-ray flux, and they can be either X, M, C, B or A class which corresponds to the logarithmic scale of $Watts/m^2$ ($10^{-4}, 10^{-5}, 10^{-6}, 10^{-7}, 10^{-8}$ respectively). You can understand better what I mean by looking at the real time lightcurves obtained from GOES satellite

These peaks have different duration depending of the flare, there are some records of flares lasting few hours where the shortest can be shorter than a minute.

All the above applies to X-ray flares, which we cannot seen from Earth, we need to put some instrument on board spacecraft or rocket so we go above the part of the atmosphere that absorbs them.

Now, if you want to see them by using an optical telescope you have two options, either using the whole visible range by projection or through an Hydrogen alpha filter. In this case the flare classification is different than in the X-ray case. Where the flare class in X-ray is measured by the enhanced of flux produced, the optical class is based by the area it covers. The Solar Influence Data Analysis Center offers a table with their properties and the corresponding X-ray flare type:

For example, the famous Carrington's event (Sept. 1, 1859) was observed and hand-drawn from Carrington by projection. But, as this article says: "He was lucky enough to be in the right place at the right time..." you need too to be quite lucky to observe one of these.

---------------------------------------------------------------
|      Area | Area            | Class | Typical corresponding |
|  (sq deg) | (10^-6 solar A) |       | SXR Class             |
---------------------------------------------------------------
|    <= 2.0 | <= 200          |     S | C2                    |
|   2.1-5.1 | 200-500         |     1 | M3                    |
|  5.2-12.4 | 500-1200        |     2 | X1                    |
| 12.5-24.7 | 1200-2400       |     3 | X5                    |
|     >24.7 | >  2400         |     4 | X9                    |
---------------------------------------------------------------

| Area (sq deg) |Area (10^{-6} solar A)|Class | Typical corresponding SXR Class| |-----------|-----------------|------:|------------------------ | <= 2.0 | <= 200 | S | C2 | | 2.1-5.1 | 200-500 | 1 | M3 | | 5.2-12.4 | 500-1200 | 2 | X1 | | 12.5-24.7 | 1200-2400 | 3 | X5 | | >24.7 | > 2400 | 4 | X9 |