Eletromagnetic radiation with a frequency below the ionosphere's plasma frequency will generally be reflected. The specific frequency depends on the density of ionospheric plasma which can vary at different altitudes, but also different geomagnetic latitudes and from day to night. For a typical daytime mid-latitude ionosphere, the most dense part of the ionosphere, (the "F" region), will reflect radio frequencies up to ~2.8Mhz (assuming an electron density of 1e11 m-3).
There are about 2e11 stars in the Milky Way galaxy. As there are about 1e11 galaxies in the universe, perhaps averaging 1e11 stars per each, that makes the number of stars in the universe roughly 1e22.For e (exponent) you could write x10^Our Milky Way i s a GALAXY. These are many billions of stars bound together in a plane. Galaxy's are not 3D. Depending on from which direction you view a galaxy it can look like a pancake, or it can just look like a line or band from left to right. We see our Milky way as a band of stars because we are viewing it from within, thus, viewing it as a line or band.