Complex sentence: It is the successor to "The Quarterly Journal of the Royal Astronomical Society", and the Royal Astronomical Society (RAS) now considers "Astronomy & Geophysics" to be its in-house journal.
Split into simpler sentences: It is the successor to the "The Quarterly Journal of the Royal Astronomical Society". As such the Royal Astronomical Society (RAS) considers "Astronomy & Geophysics" to be its in-house journal.