柚子快报激活码778899分享：20201126工作记录
1.对天文单位mjy的理解
https://irsa.ipac.caltech.edu/data/SPITZER/docs/spitzermission/missionoverview/spitzertelescopehandbook/19/
Infrared Flux Units
The infrared flux density from a point source is most commonly given in units of Jansky (Jy) where:
1 Jy = 10-23 erg s-1 cm-2 Hz-1 = 10-26 Watts m-2 Hz-1 =
The conversion between Janskys and flux density in Wm-2 per unit wavelength is given by:
1 MJy sr-1 = 2.350443 × 10-5 Jy arcsec-2.
Table A.2. Johnson system zero points
Passband
Effective wavelength (microns)
Zero point (Jy)
U
0.36
1823
B
0.44
4130
V
0.55
3781
R
0.71
2941
I
0.97
2635
J
1.25
1603
H
1.60
1075
K
2.22
667
L
3.54
288
M
4.80
170
N
10.6
36
O
21.0
9.4
Infrared Backgrounds
Various astronomical sources emit radiation in the infrared part of the spectrum. Cool stars (M class) have their peak emission just short of the near infrared. However, stars with dusty envelopes or shells and circumstellar disks can be quite bright in the infrared. Regions of star formation, HII regions, and planetary nebulae are strong infrared sources. The (relatively) cool interstellar medium in galaxies has an infrared component. There are also ultra-luminous infrared bright galaxies that are very strong sources of infrared radiation.
As in the optical, the infrared zody is concentrated toward the ecliptic with weaker emission, by approximately a factor of 4, toward the ecliptic poles. The infrared zody is strongest from about 5 microns to about 30 microns with peak emission at about 10 microns. The infrared zody has structure on most scales and, as observed from Earth, varies from season to season. The intensity of the infrared zody will also vary with solar elongation, or how close to the Sun one is pointed. The infrared zody is difficult to model.
As one moves to longer wavelengths (100 microns), diffuse Galactic emission from dust clouds in the interstellar medium becomes the dominant contribution to the infrared background. This infrared cirrus is patchy, with higher concentrations found in the Galactic disk and toward the Galactic center. However, it is important to realize that the cirrus is ubiquitous, and it is critical to examine the IRAS maps or radio maps of cirrus tracers when planning longer-wavelength observing. Far-infrared emission from external galaxies in the field of view will add to the overall background flux.
https://coolwiki.ipac.caltech.edu/index.php/Units
Brightnesses or fluxes are most likely to be given in Janskys (Jy) or mJy (milli Jy) or µJy (micro Jy). 1 Jansky = {\displaystyle 10^{-26}} Watts/m^2/Hz.
Jy can be converted to magnitudes which have historically been relatively rarely used in the mid- or far-infrared.
Because the unit is named for Karl Jansky, the plural of the unit is really Janskys, not Janskies.
Flux density is a measurement essentially of energy per unit area per unit time "per photon". In our traffic analogy, this would be the number of RED cars per lane per second that pass under the bridge on the highway. In this analogy, the "per photon" is seen in the red cars. In astronomy, the "per photon" manifests itself as a "per Hz" (unit of frequency) or "per cm" (unit of wavelength). A Jansky is proportional to Watts/m^2/Hz. Recall that Watts are energy per second. So this is energy per second per square meter per Hertz.
2.关于天文学家为什么用fits储存天文数据而不是直接拍照为jpg
FITS stands for Flexible Image Transport System, and this format is what professional astronomers use for image data. FITS images consist of a plain text header and the binary image. The header contains at least information about coordinates of the image, but may also contain a slew of other things about, for example, the target of the image, the telescope which took it, the astronomer(s) who observed it, when it was observed, the wavelength used, and any data reduction steps that may have been done to the image. The binary image can be one plane or many planes of images. It can also be a table of data.
Astronomers use FITS images because they are at least 16 or even 32 bits deep -- that is, there are at least 2 to the power of 16 ({\displaystyle 2^{16}}) or 65,536 and possibly ({\displaystyle 2^{32}}=) 4.3 billion possible discrete levels of data for each pixel. Things like jpegs or gifs are only 8 bits deep, meaning that there are only ({\displaystyle 2^{8}}=) 256 discrete levels of information for each pixel (per color plane). This is why if you make a nice image in some packages with lots of extra detail, that detail gets lost when you save it as a jpeg. The computer is compressing 65,000 levels into 256.
JPGs (and for that matter GIFs or most PNGs) are "lossy compressed" files, which means that images in those formats actually LOSE INFORMATION, particularly in comparison to the FITS file. JPGs are just fine for images you take with digital cameras - you rarely ever see evidence of the loss of information. (As an aside - you might see evidence of it if you take a picture of something with high contrast, or a sharp edge somewhere in the image. If you look at the jpeg up close, you will see 'ringing' of the sharp edge, which looks kind of like blurring. The Wikipedia page on lossy compression has an example of loss of information with JPGs.)
So, what this means is: any time you are doing science, whether that is using your eye to see small details in the image, or measuring distances, or doing photometry, you always want to be using the FITS file, never a JPG, PNG, or GIF.https://coolwiki.ipac.caltech.edu/index.php/FITS_format
3.what is a mosaic?
在这里，mosaic不能翻译为马赛克，mosaic的意思是把小的图片用计算机拼接为大的图片，我们的相机视场有限，当需要拍摄大视场时，可以分段拍摄，在拼接。
4.关于天文图像，几个重要的视频介绍https://coolwiki.ipac.caltech.edu/index.php/Astronomical_imaging
Movie (0:50) on how East is left when you are looking at the sky! -- Dr. Luisa Rebull (2015)
Movie (49:15) on Introduction to the Basics of Astronomy Data Access by Dr. Luisa Rebull (2018) 必看视频
Movie (11:39) on Color Images] by Dr. Luisa Rebull (2016)
5.关于滤光片Movie (19:53) on Filters, part of the "Filters, Magnitudes, Colors, Oh My!" playlist -- Dr. Luisa Rebull, 2020 必看视频
6.关于ds9的使用
https://coolwiki.ipac.caltech.edu/index.php/All_ds9_information_in_one_place
Measuring distances in ds9
ds9 Tutorials from Luisa's official NITARP tutorial (Jan 2013):
Part 1: ds9 overview - what is ds9, etc (10.5 min)
Part 2: the first half of the ds9 demo - getting it started, basics of usage (19 min)
Part 3: the second half of the ds9 demo - more advanced tips and tricks (25 min)
7.IRSA数据相关视频
https://www.youtube.com/channel/UCIysJbamhNnlu0Bgdrwxn_w
数据下载地址：https://irsa.ipac.caltech.edu/frontpage/
8.Accessing Kepler and CoRoT data
https://coolwiki.ipac.caltech.edu/index.php/Accessing_Kepler_and_CoRoT_data
9.NASA DATA CENTERS
http://archive.stsci.edu/footer/nasa-data-centers
nasa所有的望远镜都在这儿了
10.Spitzer Data Analysis Cookbook
https://irsa.ipac.caltech.edu/data/SPITZER/docs/dataanalysistools/cookbook/home/
非常有用的教程，建议详细阅读。
柚子快报激活码778899分享：20201126工作记录
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