🔭 Ask a Space Telescope · ถามกล้องโทรทรรศน์อวกาศ · 向太空望远镜要数据

0 What you need · ต้องมีอะไรบ้าง · 你需要什么

1 Install two libraries · ติดตั้งไลบรารีสองตัว · 装两个库

pip3 install astropy astroquery

# check it worked
python3 -c "import astroquery; print('ok')"

import sys              # comes with Python
import astropy          # you installed this

# take one piece, not the whole box
from astroquery.mast import Observations

2 See which telescopes are in there · ดูว่ามีกล้องอะไรอยู่บ้าง · 看看里面有哪些望远镜

fruit = ["mango", "papaya", "lychee"]

for name in fruit:
    print(name)         # runs 3 times

# same shape, 23 telescopes instead of 3 fruit

3 Ask one question · ถามหนึ่งคำถาม · 问一个问题

python3

from astroquery.mast import Observations

obs = Observations.query_object("M51", radius="0.01 deg")
print(len(obs))          # 1705

city = "Chiang Mai"   # a variable called city
count = 1705           # a variable called count

# now use them
print(city)            # Chiang Mai
print(count + 1)       # 1706
print(f"{city}: {count}")  # Chiang Mai: 1705

# a variable works where its value would
target = "M51"
obs = Observations.query_object(target, radius="0.01 deg")

# named arguments can swap places
query_object(objectname="M51", radius="0.01 deg")
query_object(radius="0.01 deg", objectname="M51")

4 Read what came back · อ่านสิ่งที่ได้กลับมา · 读一读回来的东西

python3

tally = {}
for row in obs:
    name = str(row["obs_collection"])
    tally[name] = tally.get(name, 0) + 1

for name, n in sorted(tally.items(), key=lambda p: -p[1]):
    print(name, n)

ages = {"Ploy": 14, "Nok": 15}

print(ages["Ploy"])          # 14
print(ages.get("Somchai", 0))  # 0, no error
print(ages["Somchai"])       # KeyError!

ages["Somchai"] = 13         # add a new pair

Those two lines, in detail · สองบรรทัดนั้น แบบละเอียด · 那两行，说细一点

The 14 printed. The 0 printed. Then the program died. Any line after it never ran. เลข 14 พิมพ์ออกมาแล้ว เลข 0 ก็พิมพ์แล้ว จากนั้นโปรแกรมก็ตาย บรรทัดที่อยู่ถัดไปไม่ได้ทำงานเลย 14 打出来了。0 也打出来了。然后程序就死了。后面的行一行都没跑。

# the long way: a real function
def by_count(pair):
    return -pair[1]

sorted(tally.items(), key=by_count)

# the short way: same thing, no name
sorted(tally.items(), key=lambda pair: -pair[1])

5 Keep only what you want · เก็บเฉพาะที่ต้องการ · 只留下你要的

python3

pics = obs[(obs["obs_collection"] == "HST") &
           (obs["dataproduct_type"] == "image")]

print(len(pics))    # 602
pics["filters", "t_exptime", "obs_id"][:5].pprint()

# pretend the column holds just 5 names
column = ["HST", "JWST", "HST", "TESS", "HST"]

# the question, asked of all 5 at once
column == "HST"
# [True, False, True, False, True]

# give that back to the table
# rows 0, 2 and 4 stay. the rest go

age = 14           # put 14 in the box
age == 14          # True  — a question
age == 15          # False
age > 10           # True

# one value:  and   |  whole table:  &
age > 10 and age < 18

6 One look is many files · หนึ่งการมอง คือหลายไฟล์ · 一次观看，是很多文件

python3

products = Observations.get_product_list(pics[:1])
print(len(products))                # 83

small = products[products["productType"] == "PREVIEW"]
small.sort("size")
small["productFilename", "size"][:3].pprint()

days = ["Mon", "Tue", "Wed", "Thu", "Fri"]

days[0]      # "Mon"   — one item
days[:1]     # ["Mon"] — a list of one
days[:3]     # Mon Tue Wed
days[-1]     # "Fri"   — count from the end

7 Download one · ดาวน์โหลดมาหนึ่งไฟล์ · 下载一个

python3

result = Observations.download_products(small[:1], download_dir="sky")

print(result["Status"][0])       # COMPLETE
print(result["Local Path"][0])   # sky/mastDownload/HST/...

name = "Ploy"
n = 1705

# f-string: the values drop into the gaps
print(f"{name} found {n} pictures")

# catch what comes back, or lose it
result = download_products(small[:1])
saved = result["Local Path"][0]

8 What you actually got · สิ่งที่คุณได้มาจริง ๆ · 你其实拿到了什么

9 The whole script · สคริปต์ทั้งตัว · 完整的脚本

ask_a_telescope.py

"""ask_a_telescope.py — ask a real archive for real data."""

import sys

from astroquery.mast import Observations

TARGET = sys.argv[1] if len(sys.argv) > 1 else "M51"


def ask(target):
    """Ask the archive what it has near one object."""
    obs = Observations.query_object(target, radius="0.01 deg")
    print(f"{target}: {len(obs)} observations")
    return obs


def count_missions(obs):
    """Which telescope took how many?"""
    tally = {}
    for row in obs:
        name = str(row["obs_collection"])
        tally[name] = tally.get(name, 0) + 1

    print("\nwho looked at it:")
    for name, n in sorted(tally.items(), key=lambda pair: -pair[1]):
        print(f"  {name:<12} {n:>5}")


def show_pictures(obs):
    """Keep only the Hubble pictures. Show a few."""
    pics = obs[(obs["obs_collection"] == "HST") &
               (obs["dataproduct_type"] == "image")]
    print(f"\nHubble images: {len(pics)}")

    columns = ["instrument_name", "filters", "t_exptime", "obs_id"]
    pics[columns][:5].pprint(max_width=140)
    return pics


def download_one(pics):
    """Get one small file. Preview files are small."""
    products = Observations.get_product_list(pics[:1])
    print(f"\nfiles in one observation: {len(products)}")

    small = products[products["productType"] == "PREVIEW"]
    if len(small) == 0:
        print("no preview in this one — try another observation")
        return

    small.sort("size")
    result = Observations.download_products(small[:1], download_dir="sky")
    print("status:", str(result["Status"][0]))
    print("saved: ", str(result["Local Path"][0]))


if __name__ == "__main__":
    found = ask(TARGET)
    count_missions(found)
    images = show_pictures(found)
    if len(images):
        download_one(images)
    print("\nAll of that was free. Nobody asked who you are.")

python3 ask_a_telescope.py
python3 ask_a_telescope.py "Orion Nebula"
python3 ask_a_telescope.py "M16"

10 Walk through the code · เดินดูโค้ดทีละส่วน · 一段一段读代码

1 — the top

import sys

from astroquery.mast import Observations

TARGET = sys.argv[1] if len(sys.argv) > 1 else "M51"

2 — ask()

def ask(target):
    obs = Observations.query_object(target, radius="0.01 deg")
    print(f"{target}: {len(obs)} observations")
    return obs

3 — count_missions()

    tally = {}
    for row in obs:
        name = str(row["obs_collection"])
        tally[name] = tally.get(name, 0) + 1

4 — show_pictures()

    pics = obs[(obs["obs_collection"] == "HST") &
               (obs["dataproduct_type"] == "image")]

    columns = ["instrument_name", "filters", "t_exptime", "obs_id"]
    pics[columns][:5].pprint(max_width=140)

5 — download_one()

    small = products[products["productType"] == "PREVIEW"]
    if len(small) == 0:
        print("no preview in this one — try another observation")
        return

    small.sort("size")
    result = Observations.download_products(small[:1], download_dir="sky")

6 — the bottom

if __name__ == "__main__":
    found = ask(TARGET)
    count_missions(found)
    images = show_pictures(found)
    if len(images):
        download_one(images)

11 When it goes wrong · เมื่อมันไม่ได้ดั่งใจ · 出问题的时候

Traceback (most recent call last):
  File "sky.py", line 7, in <module>    # where
    print(ages["Somchai"])
KeyError: 'Somchai'                     # what

# read the last line first, then the line above

12 A telescope that has not flown yet · กล้องที่ยังไม่ได้ขึ้นบิน · 一台还没上天的望远镜

python3

print(sorted(Observations.list_missions()))
# BEFS EUVE FUSE GALEX HLA HLSP HST HUT IUE K2 Kepler
# OPO PS1 SDSS SPITZER_SHA SWIFT TESS TUES WUPPE ...
# no ROMAN — not yet

13 The Python you just used · Python ที่คุณเพิ่งใช้ไป · 你刚刚用过的 Python

14 Now change it · ลองแก้ดู · 现在动手改它