Small-Body Name Parsing (sbpy.data.Names)

Names is different from the other classes in data in that it does not use DataClass as a base class. Instead, Names does not contain any data, it merely serves as an umbrella for functions to identify asteroid and comet names, numbers, and designations.

Cometary and Asteroidal Name Parsing

In order to distinguish if a string designates a comet or an asteroid, you can use the following code:

>>> from sbpy.data import Names
>>> Names.asteroid_or_comet('(1) Ceres')
'asteroid'
>>> Names.asteroid_or_comet('2P/Encke')
'comet'

The module basically uses regular expressions to match the input strings and find patterns that agree with asteroid and comet names, numbers, and designations. There are separate tasks to identify asteroid and comet identifiers:

>>> Names.parse_asteroid('(228195) 6675 P-L')
{'number': 228195, 'desig': '6675 P-L'}
>>> Names.parse_comet('73P-C/Schwassmann Wachmann 3 C')
{'type': 'P', 'number': 73, 'fragment': 'C', 'name': 'Schwassmann Wachmann 3 C'}

These methods will raise exceptions when the name cannot be parsed as expected:

>>> Names.parse_asteroid('C/2001 A2-A (LINEAR)')
Traceback (most recent call last):
...
sbpy.data.names.TargetNameParseError: C/2001 A2-A (LINEAR) does not appear to be an asteroid identifier
>>> Names.parse_comet('12893')
Traceback (most recent call last):
...
sbpy.data.names.TargetNameParseError: 12893 does not appear to be a comet name

In order to be able to distinguish between asteroid and comet identifiers, sbpy follows the MPC guideline in that it requires comet identifiers to include the comet type in either in combination with a number (e.g., '259P'), a name (e.g., 'P/Halley'), or both (e.g., '2P/Encke'). For instance, the identifier 'Halley' would be identified as an asteroid, as it lacks a comet type identifier. Hence, some caution is advised when using these routines - identification might not be unambiguous.

A/ objects: asteroids in cometary orbits

Small bodies designated with an A/ prefix have cometary orbits, but appear asteroidal [MPEC2018H54]. sbpy considers them to be asteroids:

>>> Names.asteroid_or_comet('A/2018 V3')
'asteroid'

Interstellar objects

Interstellar object designations, which start with an I/, do not give any insight into the nature of the object. For example, 1I/ʻOumuamua was asteroidal in appearance but 2I/Borisov was cometary. sbpy raises an exception for I/ objects:

>>> Names.asteroid_or_comet('1I/ʻOumuamua')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/disks/data0/astro/Projects/sbpy/sbpy/data/names.py", line 597, in asteroid_or_comet
    raise TargetNameParseError('Target nature unclear.')
sbpy.data.names.TargetNameParseError: Target nature unclear.

[MPEC2018H54]

Williams, G. V. 2018. A/ Objects. MPEC 2018-H54. https://minorplanetcenter.net/mpec/K18/K18H54.html

Sorting names with a natural sort order

Sorting with Python’s built-in functions might not return the desired order:

>>> comets = ['9P/Tempel 1',
...           '101P/Chernykh',
...           '10P/Tempel 2',
...           '2P/Encke']
>>> sorted(comets)
['101P/Chernykh', '10P/Tempel 2', '2P/Encke', '9P/Tempel 1']

101P and 10P are placed at the start of the list because Python is performing a string comparison, which is character-by-character, and '1' < '2'. With sbpy’s natural_sort_key, numerical comparisons are made whenever possible:

>>> from sbpy.data import natural_sort_key
>>> sorted(comets, key=natural_sort_key)
['2P/Encke', '9P/Tempel 1', '10P/Tempel 2', '101P/Chernykh']

Packed Numbers and Designations

from_packed and to_packed provide functionality to convert between packed designations and numbers and unpacked ones:

>>> Names.from_packed('J95A01A')
'1995 AA1'
>>> Names.from_packed('_RD0aEM')
'2027 DZ6190'
>>> Names.from_packed('G3693')
163693
>>> Names.to_packed('1995 AA1')
'J95A01A'
>>> Names.to_packed('2027 DZ6190')
'_RD0aEM'
>>> Names.to_packed('163693')
'G3693'