cmb_to_helio is broken

[dannygoldstein]

According to NED,

CMB Redshift: 8508.0 km/s (0.0284)
RA: 3.14703055556
DEC: -7.03325

corresponds to a heliocentric redshift of 8689.65 km/s or 0.0290

cmb_to_helio returns 0.0271.

[AlexGKim]

Digging a little deeper, looks like the problem is with cmb_dz. Choosing directions toward the cmb and opposite the cmb should give opposite values. They do not.

CMB_RA = 168.01190437
CMB_DEC = -6.98296811
print sndatasets.utils.cmb_dz(CMB_RA, CMB_DEC)
print sndatasets.utils.cmb_dz(CMB_RA+180, -CMB_DEC)

output is

0.0012039378391
0.00106215374604

[kbarbary]

This code was adapted from some of @rubind's code; I might have made a transcription error. Maybe David can comment?

[rubind]

I just checked the formula, and there's a typo in this version. There's a pull request for a fix.