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April 2020
This year Easter Sunday falls on April 12. However, Easter does not occur on the same date each year, and for many people, the method of deciding exactly when it does occur is a mystery. The rule is that Easter falls on the Sunday next following the Saturday that falls on or after the Full Moon next following the Vernal Equinox. This means that Easter can occur on any date from March 22 through to April 23. This year the equinox was on March 20, and the next Full Moon on Friday, April 8. Since there is that part of the rule that mentions a Saturday, the Full Moon, the required Saturday and Easter follow on successive days. The whole process of deciding the date of Easter is further complicated by the ecclesiastical authorities not using the real Full Moon but using what is called the Paschal Full Moon. It comes as no surprise that many people would prefer that the date of Easter was fixed, or had a simple rule such as being on the first Sunday in April.
The Full Moon which helps determine the date of Easter, is also dominant in the evening sky, and will hinder observation of many faint objects during the first 12 days of the month. On April 1, the Moon reaches first quarter in the constellation of Gemini the twins. With the Moon riding high in the south, enthralling views along the Moon’s terminator, which separates the night and day sides of the Moon, can be seen in binoculars or telescopes. This is a great time to encourage youngsters to see the craters and the other lunar features for the first time. They can also identify Venus as it hangs diamond-like in the western sky. A telescope will reveal that it displays phases like the Moon, at present a ‘fat’ crescent. Binoculars will show that Venus is passing close to the star cluster known as the Pleiades or Seven Sisters. By April 3, Venus will be just south of the main cluster.
In reality, this meeting of the female planet with the sisterhood is not as close as it may appear. The time taken for light to reach us from Venus decreases from 326 seconds at the beginning of the month, to 214 seconds at the end. Compare that to the 440 years that light takes to reach us from the Pleiades. When the Moon passes Venus on April 26, its light takes just 1.3 seconds to travel across the 392,000 kilometres that separate us from the Moon. That evening, both the Moon and Venus will display a crescent phase, though it will require binoculars or telescope to spot Venus’s crescent. As Venus tracks through Taurus, the Bull, it reaches a high northern declination. By the end of April it lies about 27°.8 north of the celestial equator, not far from the star Elnath, which is beta in the constellation of Taurus. The result is that Venus does not set until late in the night, indeed after midnight in the more northerly parts of Scotland. The Arctic circle will not see it set at all, and for a short period they will be ‘the land of the midnight Planet’. Conversely the Antarctic regions will not see it rise above their horizon for a similar period.
The other bright planets, Jupiter, Saturn and Mars are gathered in the morning sky as dawn begins to brighten in the south-east. They are joined by the Moon on April 15, to provide an attractive sight for those who are active during the early hours of the morning. Jupiter will be accompanied by its four Galilean Moons, Saturn will show its famous ring system, and Mars will display its russet colour than gives its title of The Red Planet.
After some months without a major meteor shower, April brings us the Lyrids. The particles that form the shower originate in comet Thatcher. This was discovered in 1861, in an orbit with a period over 400 years. At maximum, around 15-20 meteors per hour can be expected, radiating from a point near Vega, in the constellation of Lyra, the lyre. The Moon, just at new Moon, will not interfere, so observers should be on the look-out for bright fireballs at, or soon after the time of maximum on April 22.
Whilst scanning the sky for meteors, the observer will undoubtedly spot numerous satellites as they orbit the Earth. Among the most spectacular are the Starlink satellites which are launched in batches of 60 at a time. In the weeks after launch these 60 are still close together, and maybe spotted as ‘trains’ of lights each separated by a few seconds. The latest launch took place very recently. Among many other launches scheduled is an Argentian satellite call Saocom 1B. It will operate in conjunction with its twin Saocam 1A, and four Italian satellites. The size of the satellite indicates that it will be bright enough to be easily seen with the unaided eye.
April is a month of several anniversaries. The Royal observatory was opened in April 1896, the Visitor Centre in April 1981. Yuri Gagarin made the first manned orbit of the Earth in 1961, and the Hubble Space Telescope launched in April 1990. So it is celebrating 30 years of admirable research, but it is likely to be followed by the James Webb Space Telescope (JWST). This due for launch in 2021, and positioned almost one million miles from Earth. It should continue the enormous flow of astronomical data that we have received from Hubble.
Observers back here on Earth can meanwhile point their telescopes and cameras at the Full Moon that occurs on the night of April 7-8. This is a ‘Supermoon’ since it will be bigger and brighter than an average Full Moon. No doubt that the papers and other media will feature this.
Moon phases:
- First Quarter: April 1 and 30
- Full Moon: April 8
- Last Quarter: April 14
- New Moon April 23
The maps show the sky at midnight BST on the 1st, 23:00 on the 16th and 22:00 on 30th. An arrow shows the motion of Venus.
