Total lunar eclipse in Hong Kong on April 4

25 March 2015

A total lunar eclipse will occur during the evening of April 4 (Saturday) in Hong Kong. Details of the eclipse are as follows:

Similar to the eclipse on October 8 last year, a special feature of this lunar eclipse is that the eclipse is already in progress before moonrise. The total eclipse will begin about 1 hour 20 minutes after the moonrise. The duration of the whole process (from moonrise to moon leaving penumbra) will last for 4 hours 28 minutes, with the total eclipse lasting for 12 minutes. This astronomical event will be visible in Hong Kong if the weather permits.

As the elevation of the moon will be rather low during the eclipse, the event is best observed at places with an unobstructed view to the horizon in the east and southeast, such as Shek O, the east dam of High Island Reservoir and on top of Tai Mo Shan. Members of the public can also watch the event via a webcast from moonrise to the moon leaving the penumbra, which will be jointly provided by the Hong Kong Observatory (the Observatory), the Hong Kong Space Museum (the Space Museum), the Ho Koon Nature Education cum Astronomical Centre, the Po Leung Kuk Ngan Po Ling College and the HKSKH Solar Tower‧Camp on the following web page: www.weather.gov.hk/gts/event/webcast-20150404.htm.

The Space Museum will organise an observation activity titled "Night of Total Lunar Eclipse", along the middle section of the Avenue of Stars in Tsim Sha Tsui from 6:45pm to 9:45pm. The public will have the opportunity to observe the lunar eclipse through telescopes under the guidance of Space Museum staff. The activity is provided free of charge and no registration is required.

The path of the moon during the eclipse can be found in the attached diagram. An animation of the lunar eclipse and the eclipse data are also available at the YouTube channel of the Space Museum (www.youtube.com/hkspacem/) and Space Museum's mobile app "Star Hoppers" respectively. During the total eclipse, the moon will not completely vanish but will instead appear dull red in colour. This is the result of the blue part of sunlight being scattered away by the Earth's atmosphere and the remaining red light refracted onto the moon.

The total lunar eclipse on April 4 will be the third episode of the ongoing tetrad eclipse, with the first one starting on April 15, 2014. Tetrad is a term for describing four consecutive total lunar eclipses with an interval of six full moons. The remaining episode will occur on September 28 this year, but it will not be visible in Hong Kong. The last tetrad eclipse occurred from 2003 to 2004 and the next tetrad will occur from 2032 to 2033.

Please refer to the respective links at the Observatory's website for a detailed explanation of a lunar eclipse and highlights of the joint webcasting of the total lunar eclipse on October 8, 2014:
www.hko.gov.hk/gts/event/event-lunar-eclps1_e.htm and www.hko.gov.hk/hkonews/D2/sl20141010.htm .

For the weather on April 4, please refer to the latest "9-day Weather Forecast" issued by the Observatory at the following website: www.weather.gov.hk/wxinfo/currwx/fnd.htm.

As regards the astronomical observation conditions that night, please refer to the "Weather Information for Astronomical Observation" web page: http://www.hko.gov.hk/gts/astronomy/astro_portal.html.