The Sun stood still for Yehoshua prolonging the day. Hundreds of years later the day was shortened for Chizkiyahu.
Have these miracles caused observable astronomical effects?
Are there any other miracles in Tenach whose effects can be observed today?
There are a few examples of miracles that happened that we can see remnants of them even nowadays. The Dead Sea according to Jewish tradition is from the punishment of Sodom and Amorah that were destroyed by G-d because of their wickedness. What remains of that area today is an inhabitable area. Another remnant is the wife of Lot, which can be seen nowadays as a mere pillar of salt. (I am not aware of any other such pillar in the world). Another example would be from the stones of Har Sinai. The rocks of Har Sinai contain a picture of the burning bush, from which G-d spoke to Moshe, which took place on Har Sinai. No matter how you break the rock, it will always have a picture of a bush on it. (I personally own such a rock, and it is astounding to see). I am sure there are more, but this is what comes to mind right now.