There are plenty of astronomical events every year. The Hong Kong Space Museum stages a special exhibition at the foyer and online to introduce five spectacular events in 2021. The exhibition will offer observing tips on how to pick the best dates, times, locations and tools for observations.
The five spectacular events are: "lunar eclipses" on 26 May and 19 November, "Perseid meteor shower" in mid-August, "Geminid meteor shower" in mid-December and "serial phenomena of Jupiter's moons" on 15-16 August.
A total lunar eclipse and a partial lunar eclipse appeared in the evenings of 26 May and 19 November respectively. For the total lunar eclipse, the Moon will appear coppery-red near the moment of maximum eclipse. The Moon is below the horizon at the beginning of both eclipses, thus part of the eclipses is not visible in Hong Kong.
Ease of Observation
Easy
How to See?
With the naked eye or a telescope
| Total lunar eclipse 26 May 2021 |
Partial lunar eclipse 19 November 2021 |
|
When to See? |
18:56 Moonrise 19:11 Total eclipse begins 19:19 Maximum eclipse 19:26 Total eclipse ends 20:52 Partial eclipse ends 21:50 Penumbral eclipse ends |
17:38 Moonrise 18:47 Partial eclipse ends 20:06 Penumbral eclipse ends |
Where to see? |
A location with an unobstructed view of the sky and horizon in the east to southeast direction | A location with an unobstructed view of the sky and horizon in the east to northeast direction |
What to See?
The videos below simulate the telescopic and the naked eye views of the two lunar eclipses observed in Hong Kong.
Total lunar eclipse (26 May 2021)
Partial lunar eclipse (19 November 2021)
The Hong Kong Space Museum live streamed the two lunar eclipses. In addition to broadcasting the lunar eclipses, assistant curators also shared interesting tidbits related to lunar eclipse and the Moon. Recorded videos of the two live streaming programmes are included below.
Recorded video of live streaming of the total lunar eclipse (26 May 2021, narrated in Cantonese)
Recorded video of live streaming of the partial lunar eclipse (19 November 2021, narrated in Cantonese)
Why?
Dimming of the Moon occurs during a lunar eclipse since the Earth blocks part of the sunlight when the Moon enters its shadow. The Moon appears coppery-red for eclipses of large magnitude. It is because the Earth's atmosphere scatters the blue component of sunlight away, leaving the red component which is refracted by the atmosphere and illuminates the Moon.
To Know More
As the Earth casts a large shadow on the Moon, most areas on the night side of the Earth can see the eclipse. The partial lunar eclipse happened from UTC 6:01 to 12:06 (HKT 2:01 pm to 8:06 pm). Only parts of the eclipse (from partial eclipse ends to penumbral eclipse ends) were visible in Hong Kong after moonrise. On the other hand, all stages of the eclipse were visible in North America and large parts of South America. The Griffith Observatory, located in Los Angeles of U.S. live streamed the eclipse for 5.5 hours long from local time 10:00 pm and recorded the entire process of the eclipse. Click here to watch the recorded video of live streaming provided by the Griffith Observatory.
Watching from a dark rural location with a wide field-of-view, you may be able to see 20 to 30 meteors per hour under favourable weather conditions. Try the nights before and after if weather permits.
Ease of Observation
Medium
Where to see?
Go to a dark place with little light pollution, such as a rural area. Light pollution causes a significant drop in the number of observable meteors. You may not even see a single one in urban areas!
Find a site with a wide field-of-view. The wider the view of the sky, the higher the chance to see more meteors.
What to See?
The Hong Kong Space Museum live streamed the Perseid meteor shower. Although meteors were hardly found during the live streaming, audience could learn about the science behind meteor showers and the different ways of observing them from the recorded video below.
Recorded video of live streaming of the Perseid meteor shower (12 August 2021, narrated in Cantonese)
How to See?
Q: Should I gaze at the radiant?
A: Not necessarily. Meteors may appear anywhere in the sky. It is better to look everywhere.
Q: Why red light torches?
A: Red light is preferred for maintaining night vision. A red light torch can be easily made by covering a regular torch with layers of red cellophane, cloth or plastic bag.
Q: Shall I lie down and use the naked eye?
A: Yes. You'd better lie down enjoying a wide view of the sky and count the number of meteors with the naked eye.
Q: Shall I use a telescope?
A: No. The narrow field of view through a telescope decreases your chance of seeing meteors.
Why?
"Meteoroids" are natural debris and rocks sized between 0.03 mm and 1 m. A "meteor" is the streak of light crossing the sky resulting from the high-speed entry of a meteoroid into the atmosphere. A meteorite is a meteoroid falling to the ground. A "meteor shower" is formed when the Earth passes a swarm of meteoroids with similar orbits sharing a common origin.
To Know More
Click here to know more about ZHR (Zenith Hourly Rate) calculation: Meteor stream activity
A series of "transit", "eclipse" and "occultation" phenomena of all four Jupiter's Galilean moons happens within a few hours this night. "Mutual occultations" and "mutual eclipses" even occur between the moons. Mutual events are rare phenomena having a repeating cycle of roughly every six years.
Ease of Observation
Difficult
How to See?
Observe with an astronomical telescope of 20 cm aperture or more, with at least 200× magnification. A very stable atmosphere is required to observe the mutual events.
Where to see?
A location with an unobstructed view to the horizon in the east to southeast direction, and also in the southeast to southwest direction
What to See?
This videos simulate the telescopic view of the event between 17:41, 15 August and 03:10, 16 August 2021 (Hong Kong Time). (In this computer simulation, the positions of Jovian surface features such as the Giant Red Spot can differ from reality.)
Why?
Jupiter's moons are in constant orbit around Jupiter. Changes in the relative positions of the Sun, the Earth, Jupiter and Jupiter's moons lead to one of the above three kinds of phenomena. Multiple phenomena can occur simultaneously.
The mutual events between the Galilean moons are rare because their orbits are tilted slightly towards the ecliptic plane (the plane of the Earth's orbit around the Sun). Therefore, for most of the time we would see them travelling in distinct orbits around Jupiter. However, as their orbital planes also wobble as the giant planet revolves around the Sun, for roughly every six years, we will see them edge-on, giving rise to the possibility of mutual occultations and eclipses among the moons. Multiple phenomena can occur simultaneously.
The photometric observation of the quasi-simultaneous mutual eclipse and occultation between Europa and Ganymede on 22 August 2021
Paper: https://doi.org/10.1016/j.icarus.2022.115348
Paper e-print: https://arxiv.org/abs/2212.05215
