"night" shows which parts of Earth are in darkness right now (accurate to about 5 minutes in time, 100km in distance at sea level)
"light pollution" overlays the estimated sky brightness from the World Atlas of the Night Sky Brightness
"aurorae" shows the locations from which auroral activity might be visible, using data from NOAA
You can also move by ± 1 day using the keyboard left and right arrows.
optimal will find the day of the year on which the combined altitude of the objects at local midnight is maximised. It will do nothing if no objects rise.
optimal (dark time) does the same thing but only considering nights when the moon is less than 25% illuminated.
When moving by ± 1 month, surprising results may occur. For example, if you are on March 31, and you go forward one month, the date calculated is April 31, which does not exist and is interpreted instead as May 1.
This chart shows the altitude with time of the objects and the Moon on the selected day.
Blue shading represents the sky brightness due to the Moon. The density of the shading is proportional to the fractional illumination of the Moon.
If there is a change of time during the night, it is marked on the chart, but all local times still reflect the time at the start of the night.
Twilights may look very strange in the Antarctic. This is because Google's time zone resolver sets everywhere on the continent to UTC+12, which means that civil midnight can be many hours away from solar midnight.
Annual chart [?]
This chart shows the altitude of the object at local midnight throughout the year.
The grey shaded regions show the length of civil and astronomical night.
A light red dashed vertical line indicates the date shown in the daily chart.
Click on the chart to replot the daily chart for that date.
In polar regions, the altitude at local midnight will show discontinuities. This is because the definition of local midnight changes: normally half way between sunset and sunrise, it is set to 00:00 local time if the sun doesn't rise, and undefined if the sun doesn't set.
The tables in this section summarise the information presented visually above.
They include details of the objects and observing location; solar events; and moon position.
Sunset and sunrise times are corrected for refraction and the altitude of the observing location.
Lunar calculations are corrected for refraction and altitude, and are in the topocentric frame. They are slightly simplified, omitting some smaller periodic terms, but should be accurate to within a couple of minutes.
'Get extended data' gives an hour-by-hour breakdown of object and site details: altitude, azimuth, airmass, lunar distance, times, and heliocentric radial velocity correction (with the parts due to Earth's rotation and orbit indicated). Subtract these corrections from an observed velocity to apply them.