OMEGA OBSERVATORY

About this website

Rights and privacy

This page explains how the site's material may be used, how the observation data should be understood and how information is handled when you use the contact form.

About this website

The Omega Observatory website is an observation-driven archive for documenting and publishing astronomical observations. It also provides information about the observatory, its telescopes and other instruments.

© 2026 Omega Observatory. Unless otherwise stated, the site's text, observation notes, photographs, sketches and other material are protected by copyright. Contact Omega Observatory through the contact form with questions about use or publication.

Photographs and sketches were produced by Omega Observatory unless another creator or source is stated. Material from other creators is published with permission or under the stated licence.

Nature of the observations

The observation reports document the conditions and the observer's visual assessment at the time of observation. Values such as seeing, transparency, NELM and Bortle class should therefore be understood as observation data and assessments, not guaranteed measurements, unless otherwise stated.

Star chart sources

The J2000 star positions and magnitudes used in the site's charts are based on ESA's Hipparcos catalogue via CDS. Object positions were checked against CDS SIMBAD. The constellation line figures use open data from d3-celestial under the BSD 3-Clause licence. The charts are pre-generated by Omega Observatory and are intended as orientation charts. The overview chart uses a simplified stellar background with stars down to approximately magnitude 5.5 to make constellations and observed objects easier to locate.

Observation planning and astronomical times

The home page provides an overview of the current observing night. The separate Planning page can be used for today, tomorrow or a custom date within the actual coverage of the SMHI forecast. The date refers to the evening when the observing night begins. Solar and lunar positions, rise and set events, the Moon's meridian passage, and the illuminated fraction of the Moon are calculated locally on the server using Meeus-based astronomical algorithms; SunCalc has been used as a methodological and implementation reference. Astronomical darkness is the period when the Sun's centre is at least 18° below the horizon. The moon-free observing window is the part of astronomical darkness during which the Moon is also below the horizon. If the Moon remains above the horizon throughout astronomical darkness, the moon-free observing window is 0 h 00 min.

All times are converted individually to Europe/Stockholm. CET or CEST is stated once for the observing night, except when the night spans the clock change itself; in that case the zone is shown with each affected time. Approximate rise, meridian passage, set, visual magnitude and elongation for the planets, Ceres and Pluto are calculated for the selected calendar day. If a following meridian passage or set occurs after midnight, the actual following date is shown. Planetary observing suitability is a geometric planning assessment based on elongation and altitude during relevant twilight or darkness. Moonlight is not included in the planetary assessment.

The “Constellations suitable for observation” section is calculated on the server and uses the moon-free observing window. The calculation applies a practical altitude limit and identifies constellations that are favourably positioned above the southern horizon. The constellation boundaries are based on Roman et al. 1987 (CDS/VizieR VI/42). Only constellations with a contiguous and practically relevant part above the southern horizon are included. Best time means the time when the practically available part of the constellation is, on average, most favourably positioned above the southern horizon.

Total cloud cover, low-, medium- and high-level cloud cover, precipitation probability and amount, temperature and relative humidity are fetched separately from SMHI's SNOW1gv1 meteorological forecast. When astronomical darkness occurs, total cloud cover is shown as a time-resolved forecast from its beginning to its end. Values at the beginning and end are interpolated when necessary between neighbouring SMHI forecast points, while the forecast points in between are shown at the time resolution available in the forecast. During the part of the year when astronomical darkness does not occur, an evening-and-night interval is used instead for the meteorological summary. The forecast's actual final valid time controls how far ahead a custom date can be selected; the whole observing night through astronomical dawn the following morning must be covered. Dew point is calculated from forecast temperature and relative humidity and is used to show the minimum dew-point margin and a simplified condensation-risk assessment. Meteorological conditions are assessed on a simplified five-level scale. Mean total cloud cover gives the base score: up to 10% gives 5, above 10–30% gives 4, above 30–55% gives 3, above 55–80% gives 2 and above 80% gives 1. The maximum precipitation probability during the period may then cap the assessment at 4 for 20–29%, 3 for 30–49%, 2 for 50–69%, and 1 for 70% or more. A high condensation risk then lowers the assessment by one further level where possible. The separate cloud layers are also used as a technical plausibility check of SMHI's total cloud-cover value but do not automatically replace it. The forecast reference time is shown on the planning page. If SMHI is temporarily unavailable, server-cached fallback data no more than one hour old may be used and this is then stated on the page. Moonlight, seeing and astronomical transparency are not included in the meteorological assessment. If no forecast data are available, the custom date field is disabled while the astronomical calculations for today and tomorrow can continue to operate.

Questions about the website's material, privacy or information you have submitted can be sent through the contact form. Do not send sensitive personal information.