查看“Astropy”的源代码

== astropy.io.fits ==
[http://docs.astropy.org/en/stable/io/fits/]

 >>> hdulist = fits.open('input.fits')
 >>> hdulist.info()

===header===
*each element of an HDUList is an HDU object with .header and .data attributes, which can be used to access the header and data portions of the HDU.
 >>> hdulist[0].header['targname']

*To see the entire header as it appears in the FITS file (with the END card and padding stripped), simply enter the header object by itself, or print(repr(header)):
*It’s also possible to view a slice of the header:
 >>> header[:2]
*Another way to either update an existing card or append a new one is to use the Header.set() method:
 >>> prihdr.set('observer', 'Edwin Hubble')

===fits table 的读与写===
*写 
 from astropy.table import Table
 t=Table([Bage,fzbin,Age_weight2],names=('Age','z','weights'))
 t.write('SFH_LMC3_out.fits',format='fits')
*读
 hdu = fits.open('SFH_LMC3_out.fits')
 hdu.info() #看看哪些hdu
 data=hdu[1].data
 data.columns #看看有那些列
 Bage=data.field('Age')

===fits文件打开过多错误===
* [https://docs.astropy.org/en/stable/io/fits/appendix/faq.html#i-am-opening-many-fits-files-in-a-loop-and-getting-oserror-too-many-open-files]
* fits.close() 
* 可能还根系统设置有关  
 ulimit -a
 ulimit -n 100000
 vim /etc/security/limits.conf
* 把python的软限制编程硬限制,参见 https://bbs.huaweicloud.com/blogs/108323
 import resource
 soft, hard = resource.getrlimit(resource.RLIMIT_NOFILE)
 resource.setrlimit(resource.RLIMIT_NOFILE, (hard, hard))
*lsof -p 进程id > openfiles.log命令，获得当前占用句柄的全部详情进行分析
* 实测这两个效果不好（python 3.8）
:*del hdu.data
:*hdu = fits.open(fits_name,memmap=False) #打开fits文件数目比较多的情况下

==fits image读写==
 n = np.arange(100.0) 
 hdu = fits.PrimaryHDU(n)
 hdu.writeto('new2.fits')
 hdu.writeto('new2.fits')
*如果超过一个hdu
 >>> hdul = fits.HDUList([hdu])
 >>> hdul.writeto('new1.fits')

==astrometry==
*match 两个星表
 >>> from astropy.coordinates import SkyCoord
 >>> from astropy import units as u
 >>> c = SkyCoord(ra=ra1*u.degree, dec=dec1*u.degree)  
 >>> catalog = SkyCoord(ra=ra2*u.degree, dec=dec2*u.degree)  
 >>> idx, d2d, d3d = c.match_to_catalog_sky(catalog)
 >>> sel=np.where(d2d.degree < 0.00002)

==宇宙学==
http://docs.astropy.org/en/stable/cosmology/
*从红移到年龄
 >>>from astropy.cosmology import FlatLambdaCDM 
 >>>cosmo = FlatLambdaCDM(H0=70, Om0=0.3)
>>> lum_dis=cosmo.luminosity_distance(redshift) #计算光度距离

*从年龄到红移
 >>> import astropy.units as u
 >>> from astropy.cosmology import  z_at_value
 >>> z_at_value(cosmos.age, 2 * u.Gyr)

==单位转换==
 dL=lum_dis.to(u.cm)