A database-less package for performing astronomical calculations with any third-party database of deep-sky objects.

Features

alpha_lib can accurately calculate the altitude and azimuth of a deep sky object at any location or time.

The local or Greenwich mean sideral time and Julian date can also be calculated, in addition to other numerical values regarding the Sun and timekeeping.

Furthermore, alpha_lib can calculate the rise and set times of an object, in addition to when (and where) an object will "peak" in the sky.

The current implementation of coordinate filtering is probably suboptimal, but it can indicate the times an object is above a certain altitude or within a certain azimuth range.

Usage

Use the DeepSky class to create a deep sky object. I hope to implement a class for heliocentric objects (that also extends SkyObject) soon.

All astronomical values will be returned as radians.

Time values are returned as hours, which can be appended to the day, month, and year of time for a specific date and time.

The constructor parameters minAz, maxAz, and minAlt are optional and used for coordinate filtering.

import 'dart:math';
DeepSky andromeda = DeepSky(latitude: 40.5, longitude: -72.1, raRad: 0.01243, decRad: 0.7191, time: DateTime.timestamp(), utcOffset: -5, minAz: 200, maxAz: 300, minAlt: 40);

To get the object's altitude and azimuth at that time, use the altAz method.

final altAz = andromeda.altAz;
print(altAz);

//[0.23092634227782138, 0.8105940619838048] -- the altitude, azimuth in radians 

// To convert altitude to degrees
print(altAz[0].toDegrees(Units.radians));

// 13.231104790912635 -- the Andromeda Galaxy is currently 13.2 degrees above the horizon

To get the local times, expressed in radians, when the object is within the minAz, maxAz, and minAlt filters, use the withinFilters method. This is useful for astronomers with obstructed views of the sky.

print(withinFilters);
// [4.9567..., 5.995205...] -- the object is within azimuths 200° and 300° and 40° above the horizon between those two times
// In hours, those values are about 19:00 and 23:00.

To get the hours an object will set, expressed in radians, use the localRiseSetTimes or utcRiseSetTimes methods. If an object never sets, its rise and set times will be returned as [0, 0]. If an object never rises, its rise and set times will be returned as [-1, -1].

To get information about an object's peak, use the peakInfo method. It returns a Map<String, double> with keys 'alt', 'az', 'time' and their corresponding values, with time expressed in radians.

Deep-sky objects are, generally, only visible at night. The sky is darkest after astronomical twilight, at which point deep-sky objects start to become visible if they are above the horizon. For the times at which the sky is dark and the object is above the horizon, use hoursVisible. If there are no such times, hoursVisible will return [-1, -1].

The hoursSuggested method is like a synthesis of hoursVisible and withinFilters. It returns, in radians, the times at which an object is visible and within the user-defined filters.

Additional information

Please file issues, suggestions, pull requests, etc. on the GitHub repository and I will try to respond to them. I am currently applying to colleges, so I may be a little busy. Most notably, the withinFilters method could probably use some improving.