Пример:
from astropy.io import fits
import numpy as np
import matplotlib.pyplot as plt
## Read
hdul = fits.open('yourfile.fits')
image = hdul[0].data
Ny, Nx = image.shape
## Mean (careful if the unit is MJy/sr)
avg = np.nanmean(image)
print('Image mean = ', avg)
## Plot (mark bright spots)
xl = []
yl = []
for x in range(Nx):
for y in range(Ny):
if image[y,x]>avg:
xl.append(x)
yl.append(y)
plt.imshow(image)
plt.scatter(xl, yl, c='r', marker='o')
plt.show()