catch-that-asteroid.myst.md

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Catch that asteroid!

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First, we need to increase the timeout time to allow the download of data occur properly:

from astropy.utils.data import conf

conf.dataurl

conf.remote_timeout

conf.remote_timeout = 10000

Then, we do the rest of the imports:

from astropy import units as u
from astropy.time import Time, TimeDelta
from astropy.coordinates import solar_system_ephemeris

solar_system_ephemeris.set("jpl")

from hapsira.bodies import Sun, Earth, Moon
from hapsira.ephem import Ephem
from hapsira.frames import Planes
from hapsira.plotting import OrbitPlotter
from hapsira.plotting.misc import plot_solar_system
from hapsira.twobody import Orbit
from hapsira.util import norm, time_range

EPOCH = Time("2017-09-01 12:05:50", scale="tdb")
C_FLORENCE = "#000"
C_MOON = "#999"

Earth.plot(EPOCH)

Our first option to retrieve the orbit of the Florence asteroid is to use Orbit.from_sbdb, which gives us the osculating elements at a certain epoch:

florence_osc = Orbit.from_sbdb("Florence")
florence_osc

However, the epoch of the result is not close to the time of the close approach we are studying:

florence_osc.epoch.iso

Therefore, if we propagate this orbit to EPOCH, the results will be a bit different from the reality. Therefore, we need to find some other means.

Let's use the Ephem.from_horizons method as an alternative, sampling over a period of 6 months:

epochs = time_range(
    EPOCH - TimeDelta(3 * 30 * u.day), end=EPOCH + TimeDelta(3 * 30 * u.day)
)

florence = Ephem.from_horizons("Florence", epochs, plane=Planes.EARTH_ECLIPTIC)
florence

florence.plane

And now, let's compute the distance between Florence and the Earth at that epoch:

earth = Ephem.from_body(Earth, epochs, plane=Planes.EARTH_ECLIPTIC)
earth

min_distance = norm(florence.rv(EPOCH)[0] - earth.rv(EPOCH)[0]) - Earth.R
min_distance.to(u.km)

This value is consistent with what ESA says! $7\,060\,160$ km

abs((min_distance - 7060160 * u.km) / (7060160 * u.km)).decompose()

from IPython.display import HTML

HTML(
    """<blockquote class="twitter-tweet" data-lang="en"><p lang="es" dir="ltr">La <a href="https://twitter.com/esa_es">@esa_es</a> ha preparado un resumen del asteroide <a href="https://twitter.com/hashtag/Florence?src=hash">#Florence</a> 😍 <a href="https://t.co/Sk1lb7Kz0j">pic.twitter.com/Sk1lb7Kz0j</a></p>&mdash; AeroPython (@AeroPython) <a href="https://twitter.com/AeroPython/status/903197147914543105">August 31, 2017</a></blockquote>
<script src="//platform.twitter.com/widgets.js" charset="utf-8"></script>"""
)

And now we can plot!

:tags: [nbsphinx-thumbnail]

frame = plot_solar_system(outer=False, epoch=EPOCH)
frame.plot_ephem(florence, EPOCH, label="Florence", color=C_FLORENCE)

Finally, we are going to visualize the orbit of Florence with respect to the Earth. For that, we set a narrower time range, and specify that we want to retrieve the ephemerides with respect to our planet:

epochs = time_range(
    EPOCH - TimeDelta(5 * u.day), end=EPOCH + TimeDelta(5 * u.day)
)

florence_e = Ephem.from_horizons("Florence", epochs, attractor=Earth)
florence_e

We now retrieve the ephemerides of the Moon, which are given directly in GCRS:

moon = Ephem.from_body(Moon, epochs, attractor=Earth)
moon

plotter = OrbitPlotter()
plotter.set_attractor(Earth)
plotter.set_body_frame(Moon)
plotter.plot_ephem(moon, EPOCH, label=Moon, color=C_MOON)

And now, the glorious final plot:

from matplotlib import pyplot as plt

frame = OrbitPlotter()

frame.set_attractor(Earth)
frame.set_orbit_frame(Orbit.from_ephem(Earth, florence_e, EPOCH))

frame.plot_ephem(florence_e, EPOCH, label="Florence", color=C_FLORENCE)
frame.plot_ephem(moon, EPOCH, label=Moon, color=C_MOON)