I recommend starting on day 28 (night), and finishing on day 29 (day), as they are fairly easy to complete. They are also night and day, which is important as some of the suns are only available during certain times. Also, all pigs have to be dead before shooting the stars, otherwise they will not register, and in turn, the sky won't change colour.

One can be found on top of the barn without a door. It is on the end of the roof on the left side. To get up onto the roof "Boar Milk" is needed. This can easily be purchased after putting all of the pigs you just killed into the grinder. Simply jump onto the lower roof, then up again, onto the higher roof. Using your flashlight makes it much easier to spot.



The next one is located on the back side of a fence, that is to the left of the main barn. It is easily seen with the flashlight.








The final sun available at night is underneath the building that houses the electrical fence switch. The flashlight is need for this one to even be visible.







However if you a still struggling to shoot it, you can change the camera angle using "F10"; this can make it even easier to see.

The First sun is rather easy to spot in the day, as it spawns in the barn. It is at the apex of the barn above the door. Once shot, the farmer will start to sing the first few lines of the chorus of " Stressed Out ", by twenty one pilots.






The next one can be found near the door on the building that houses the electrical fence switch (above the one shown previously). To get this one, you have to stand back in the barn and shoot it. The farmer will also sing a few more lines from the chorus. Thanks to Ahoron for letting me know how to get this "Trickshot"!





The final sun that can be shot for the achievement is inside the grain silo that has fallen over. It can be hard to see from the open end of the silo, but is more visible from the end that is more closed off.

I hoped this guide helped you in some way. If you find any mistakes let me know in the comments below and I will make changes accordingly.