What's In My... SKY - setiastro/setiastrosuitepro GitHub Wiki

Function: What’s In My Sky

Quickly list visible targets for a given place and time. Computes alt/az, minutes to transit, moon separation, and a phase icon, then shows the N closest-to-transit objects from your catalog filters.

What it does

  • Converts catalog RA/Dec → Alt/Az for your latitude/longitude, date/time, and time zone.
  • Computes Local Sidereal Time (LST) and each object’s minutes to transit.
  • Filters objects by minimum altitude and selected catalogs.
  • Adds angular separation from the Moon and lunar phase % (plus an icon).
  • Lets you sort, open object pages, toggle RA/Dec format, export CSV, and append custom objects to the on-disk catalog.

Inputs (left panel)

  • Latitude, Longitude (deg)
  • Date YYYY-MM-DD, Time HH:MM
  • Time Zone (IANA list)
  • Min Altitude (deg, 0–90)
  • Catalog Filters (checkboxes): Messier, NGC, IC, Caldwell, Abell, Sharpless, LBN, LDN, PNG, User
  • Object Limit (in settings): how many nearest-to-transit objects to return

Outputs (table columns)

  1. Name
  2. RA / Dec (toggle Degrees ↔ H:M:S / D:M:S)
  3. Altitude (deg)
  4. Azimuth (deg)
  5. Minutes to Transit (sorted ascending by default)
  6. Before/After Transit (“Before” if transiting ahead, “After” otherwise)
  7. Degrees from Moon
  8. Alt Name
  9. Type
  10. Magnitude
  11. Size (arcmin)

Auxiliary:

  • Status updates
  • Local Sidereal Time
  • Lunar Phase % and icon

Core calculations

All sky coordinates are evaluated at the given place and time using Astropy.

Alt/Az transform

(\alpha,\ \delta)\ \xrightarrow[\text{obstime,\ location}]{\text{ICRS}\to\text{AltAz}}\ (\mathrm{Alt},\ \mathrm{Az})

Local Sidereal Time (reported by Astropy as apparent LST)

\mathrm{LST}\ \text{at longitude }\lambda

Minutes to transit (object crossing the local meridian). Let RA in hours be ( \mathrm{RA}_h ), and LST in hours be ( \mathrm{LST}_h ).

\Delta t_h = (\mathrm{RA}_h - \mathrm{LST}_h)\ \bmod\ 24

Map to the nearest crossing within 12 hours and convert to minutes:

\mathrm{MinutesToTransit}=
\begin{cases}
60\,\Delta t_h, & \Delta t_h \le 12 \\
60\,(24-\Delta t_h), & \Delta t_h > 12
\end{cases}

We also label:

\text{Before/After}=
\begin{cases}
\text{Before}, & \Delta t_h \le 12 \\
\text{After}, & \Delta t_h > 12
\end{cases}

Lunar phase percentage from Sun–Moon elongation (E) (deg):

\mathrm{Phase\%} = 100 \times \frac{1 - \cos(E\,\pi/180)}{2}

A second evaluation 6 hours later determines waxing/waning to pick the proper crescent/gibbous icon.

Separation from the Moon

\mathrm{Sep}_{\text{Moon}} = \arccos\big(\hat{s}\cdot\hat{m}\big)\ \ (\text{reported in degrees})

Workflow

  1. Enter location, date/time, time zone, min altitude.
  2. Tick desired catalogs.
  3. Click Calculate.
  4. Sort columns as needed (default is Minutes to Transit ascending).
  5. Double-click a row to open an AstroBin search for that object.
  6. Toggle RA/Dec format at any time.
  7. Save to CSV (exactly the columns you see).

Catalog & custom objects

  • The tool reads celestial_catalog.csv from your home folder. If missing, a bundled copy is written there on first use.
  • Add Custom Object appends a row (Name, RA deg, Dec deg, Catalog=User, etc.) to that CSV so it appears in future runs.

Notes

  • RA/Dec values in the table can be shown in degrees or sexagesimal; conversion is done on the fly.
  • If gain or magnitude fields are blank in the source CSV, they remain blank in results.
  • Sorting of numeric columns is aware of numbers; others sort lexicographically.
  • The object limit (default 100) can be changed via the wrench/settings button.

Tips

  • Increase Min Altitude to screen out low, turbulent targets.
  • Use Degrees from Moon to avoid lunar glow; larger is generally better for faint DSOs.
  • For a real-time plan, re-run hourly (or change time) and watch Minutes to Transit tighten toward zero.