astroplan Tutorial 1

I'm long overdue for a post about my Google Summer of Code project with astropy, called astroplan. For background on GSoC and astroplan, see this earlier blog post.

Why so silent?

I haven't posted in a while because, well, we've been working on the code! You can see the progress in our GitHub repository, where I've made a few big contributions over the past few weeks in pull requests 11 and 14. Most of the discussion about the development of the core functionality of astroplan is in those pull requests. 

Quick Tutorial: observation planning basics

Say you're going to observe sometime in the near future, and you need to figure out: the time of sunrise and sunset, the altitude of your target at a particular time from your observatory, and when the target next transits the meridian. Let's use Vega as our target and Mauna Kea as the location of our observatory, and use astroplan to find the answers:

from astropy.coordinates import EarthLocation
from astropy.time import Time
from astroplan import Observer, FixedTarget
import astropy.units as u

# Initialize Observer object at the location of Keck
keck = EarthLocation.from_geodetic('204d31m18s', '19d49m42s', 4160)
obs = Observer(location=keck, timezone='US/Hawaii')

# Initialize FixedTarget object for Vega using from_name
vega = FixedTarget.from_name('Vega')

# Pick the time of our observations in UTC
time = Time('2015-07-09 03:00:00')

# Calculate the time Vega rises above 30 degress: 
next_rise_vega = obs.calc_rise(time, vega, horizon=30*u.deg)
print('Vega rises: {0} [ISO] = {1} [JD]'.format(next_rise_vega.iso, next_rise_vega.jd))

The above code returns:

Vega rises: 2015-07-09 05:24:22.732 [ISO] = 2457212.72526 [JD]

The time at next rise is an astropy Time object, so it's easy to convert it to other units. Now let's do the rest of the calculations:

# Calculate time of sunrise, sunset
previous_sunset = obs.sunset(time, which='previous')
next_sunrise = obs.sunrise(time, which='next')
print('Previous sunset: {}'.format(previous_sunset.iso))
print('Next sunrise: {}'.format(next_sunrise.iso))

# Is Vega up at the present time?
vega_visible = obs.can_see(time, vega)
print('Is Vega up?: {}'.format(vega_visible))

# When will Vega next transit the meridian?
next_transit = obs.calc_meridian_transit(time, vega, which='next')
print("Vega's next transit: {}".format(next_transit.iso))

prints the following:

Previous sunset: 2015-07-08 05:02:09.435
Next sunrise: 2015-07-09 15:53:53.525
Is Vega up?: True
Vega's next transit: 2015-07-09 09:51:18.800

Now let's say you need a half-night of observations. What are the times of astronomical sunrise/sunset and midnight?

# Sunrise/sunset at astronomical twilight, nearest midnight:
set_astro = obs.evening_astronomical(time, which='previous')
rise_astro = obs.morning_astronomical(time, which='next')
midnight = obs.midnight(time)
print('Astronomical sunset: {}'.format(set_astro.iso))
print('Astronomical sunrise: {}'.format(rise_astro.iso))
print('Midnight: {}'.format(midnight.iso))

which prints:

Astronomical sunset: 2015-07-08 06:29:05.259
Astronomical sunrise: 2015-07-09 14:27:05.156
Midnight: 2015-07-09 10:27:59.015

You can also view this code in an iPython Notebook here.

Introduction to GSoC 2015

What is Google Summer of Code?

Google Summer of Code is a really great opportunity for early-career astronomers to learn to code with forethought for open source projects that will actually get used by other astronomers — something we often aspire to do, but are rarely taught to do. To begin a GSoC project, you work one-on-one (or in my case, two-on-one) with mentors who are experienced open source developers to prepare a proposal for a software tool you would like to make with their help, including a detailed description of the project's deliverables and timeline.

In the astronomical world, one source of GSoC projects is astropy, our friendly neighborhood Pythonic astronomical Swiss-army knife. There are projects related to the active development on the "core" guts of astropy — like one proposed project by UW graduate student Patti Carroll — in addition to projects on affiliated packages which make use of astropy to do new things for more specific end-users than astropy core.

Your proposal gets written up in a wiki page on the astropy GitHub repository, where it can be revised with the help of your proposed mentors.

My GSoC2015 project: astroplan

My GSoC 2015 proposal is to help co-develop astroplan (heads up: as of posting in May 2015, this repo will be boring), an observation planning and scheduling tool for observational astronomers. This package will allow observers to enter a table of astronomical targets and a range of observing dates in order to retrieve (1) the sky-coordinates for their targets, (2) rise/set times, moon/sun separation angles, airmass ephemerides, and other essential positional criteria necessary for determining the observability of a target, and (3) a roughly optimized observing schedule for the list of targets. This project will take advantage of the already-developed infrastructure for these calculations in the coordinates, time, and table modules of astropy, plus Astroquery — an astropy-affiliated package. If you don't already know about these powerful tools, check them out!

I will be working with a great team of astroplanners including mentors: Eric Jeschke, Christoph Deil, Erik Tollerud and Adrian Price-Whelan, and co-developer Jazmin Berlanga Medina.

Call for input

Since we want astroplan to be useful and used by astronomers, I'd be happy to hear your thoughts on what astroplan absolutely must do. If you think you might be an astroplan user one day, leave a comment below or on Twitter with your top-priority observation planning/scheduling features.