## The Astronomers’ Magic Envelope

The Astronomers' Magic Envelope is an introduction to astrophysics
emphasizing general principles and orders of magnitude. The envelope
is metaphorical, of course --- it could also be a Python IDE. We
begin with the Enlightenment-era insight that the orbits of the
planets are easy, but the orbit of the Moon is a real headache, and
continues to deterministic chaos. Then we proceed to spacetime and
black holes, how stars work, and beyond to 21st-century developments
on microwave background and gravitational waves. Check out the
preprint.

### Errata

The pessimistic comment by Simon Newcomb at the end of the 19th
century, which we quote in Chapter 4, comes from an address on The Place of Astronomy Among the Sciences. Thanks to
Barbara Ryden for pointing this out.

The last equation in Chapter 4 needs an extra constant factor
of *m*^{4}/(3π^{2}). Corrected by
Nastassia Grimm

Between equations (4.33) and (4.34): the sum of inverse fourth
powers should be π^{4}/90 (not
π^{2}/90). Corrected by Ugur Gültekin.

Further corrections welcome.