Gregorian/Lunar Calendar
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  • An extra-large full moon for the Mid-Autumn Festival

  • Friday, 18th September 2015

There is something different about this year's Mid-Autumn Festival. If the weather is fine, the public will see an extra-large "super moon" hanging in the night sky of Hong Kong. To assist moon-watching by the public, the times of moonrise, transit and moonset during the Mid-Autumn Festival period are given below. At transit, the moon passes the local meridian due south and its elevation is the highest of the night.

September 26 (Saturday) - the eve of the Mid-Autumn Festival  
Moonrise 4.52pm
Transit (Elevation 62 degrees) 10.54pm
Moonset 5am (next morning)
September 27 (Sunday) - Mid-Autumn Festival  
Moonrise 5.40pm
Transit (Elevation 67 degrees) 11.50pm
Moonset 6.04am (next morning)
September 28 (Monday) - the day following the Mid-Autumn Festival  
Lunar Perigee (The moon is below the horizon of Hong Kong at this moment) 9.46am
Full Moon (The moon is below the horizon of Hong Kong at this moment) 10.51am
Moonrise 6.28pm
Transit (Elevation 72 degrees) 0.46am (next morning)
Moonset 7.09am (next morning)

Although the full moon (Note 1) will occur on the morning of the day following the Mid-Autumn Festival, a bright moon will still be on full view on the evening of the Festival, as well as the early hours of the next day and the following night, weather permitting. During the period, the Moon will be near the perigee (closest point to the Earth) at a distance of around 357,000 km. The diameter of the Moon as observed through naked eyes from the Earth will appear around 7 per cent (Note 2) larger than that seen when the Moon is at an average distance from the Earth. This will be visually the biggest Mid-Autumn moon since 1998. While a total lunar eclipse will occur in South America, most parts of North America, Europe, Africa and western Asia during the full moon, people in Hong Kong will miss out on this astronomical phenomenon. The next time a "super moon" and a total lunar eclipse to occur concurrently will be in 2033.

For the moon phase information and the latest weather conditions during the Mid-Autumn Festival period, please refer to the Weather Information for Astronomical Observation webpage (www.hko.gov.hk/gts/astronomy/astro_portal.html) and the 9-day Weather Forecast issued by the Hong Kong Observatory (www.weather.gov.hk/wxinfo/currwx/fnd.htm) respectively for the planning of moon-watching activities.

Note 1: At full moon, the Moon as seen from the Earth is completely illuminated with the Moon and the Sun located on the opposite sides of the Earth.

Note 2: If the comparison is based on the visual size of the moon at perigee (visually the biggest) and that at apogee (visually the smallest), the difference in visual diameter will be around 14%.

Figure 1
Figure 1. Merged photo comparing the visual size of the Moon at the perigee (left) and at average distance from the Earth (right). (Courtesy of the Hong Kong Space Museum.)