Earth, present time or very near future. Astronomers have just announced that it is believed that almost 9 billion habitable Earth-like planets exist in the Milky Way alone (this is true, but there is much scepticism over the number).
World bodies convene, and decide that we should try and communicate our presence, and think about ways we could catch the attention of another civilisation.
Now, the most obvious part of our solar system is the Sun itself, and my question is this - how would you, using current or soon feasible technology, alter the luminosity of the Sun in a way that is:
- Noticeable from at least 100 light years away (think about the fluctuations we can detect in stars a similar distance away).
- Doesn't cause permanent change to in the Sun (effects are temporary).
- Doesn't negatively impact life on our planet (effect is either not dangerous or too short an interval to damage us).
I'm thinking something that causes to Sun to flare brighter or dimmer for a short period of time, or maybe even changing the colour it emits of that is possible, by introducing foreign objects into the Sun, but I'm open to any ideas! Obviously the more feasible and repeatable over time, the better (I'm hoping this could be a sustainable form of communication), so if your method is dangerous, but not in short bursts, please consider the interval required between repeats in order to maintain safe use.
Note that an answer saying "you can't do this without causing damage to us or the Sun" is perfectly acceptable, provided it's true!
Things I'm not looking to consider:
The method of communication - that's a different problem. I just want to be able to make the Sun look different from very far away for a short but detectable period of time, should a people with similar levels of technology to us be looking.
The wisdom of doing it in the first place - no "just inviting invasion" discussions please.
"The chances that someone would see it are tiny" or "probably no one would see it for hundreds of years". I'm not interested in the probability of life on other planets.
P.S. I know a similar question has been asked about using the Sun as a giant signal lamp, but it specifically referred to the use of a Dyson sphere which is way beyond our level of technology. I'm looking for something that alters what the Sun looks like from far away, not something that physically blocks it at intervals.