Stargazing: How to see the year's first shooting stars

Not everyone knows that the dating of Easter is based on astronomical phenomena and one of the most complex calculations ever attempted.

This calculation is known in Latin as the “computus paschalis” or calculation of Easter, and is where we get our word “computer” from.

The calculation follows a formula, first proposed by a Greek mathematician and astronomer, Dionysius Exiguus at the First Synod of Nicaea in 325 AD. He declared that Easter should be the first Sunday after the first Full Moon after the Vernal Equinox except when the Full Moon falls on a Sunday, then Easter Sunday shall be one week later. This means that Easter can occur

This situation arose because different churches, from the Roman Catholic to the Eastern Orthodox had been calculating Easter with reference to the Hebrew calendar and the date of Passover and each were using their own, local calendars which had fallen out of sync with each other (and the Hebrew calendar) with the result that Easter was celebrated on different days in different churches. This was unacceptable.

Complications within the calculations arose from the “slippage” in the observed motions of the Sun and Moon caused by the precession of the Earth’s orbit. This is a periodic “wobble” of the planet around its axis with the result that the Vernal Equinox, itself, did not always fall on the same day until The Church of Alexandria decided that March 21st should be the “ecclesiastical” date of the equinox irrespective of astronomical observation.

Throughout this time these calculations were made using the Julian Calendar (named after Julius Ceasar) which is a Solar Calendar of exactly 365 days and still had to be periodically “adjusted” to keep the date of Easter correct. Then, in 1582, Pope Gregory XIII introduced the “Gregorian” calendar (which is also a Solar calendar, but of 365¼  days) as a means of keeping better track of the equinox and the date of Easter.  Confusion now arose based on which of these calendars each church followed.

The Gregorian calendar was devised to correct the increasing error in the Julian.  When it was introduced on Thursday 4th October 1582, that date was immediately followed by Friday 15th October 1582. Riots followed as some people believed that the Pope had stolen 11 days of their lives.

This calendar reform and these calculations are still being made and “adjusted” to this day which is where the introduction of a “leap year” comes in. The formula currently used is an approximation based on an approximation, so errors inevitably creep in and we are still adding “leap seconds” to the calendar in order to keep it in line..

Skynotes

Please note all times given in this article are in GMT so remember to add an hour to get the time in BST which started on Sunday 30th March.

Sun: On the 1st April, the Sun rises at 06:47 and remains in the sky for 13 hours. This means that it does not get truly, astronomically, dark until about a quarter to ten. By the end of the month, the sun rises at 05:48 and remains in the sky for 14 ½ hours so that astronomical darkness does not fall until around 11 o’clock.

Mercury:  Mercury is too close to the Sun to be visible this month.

Venus: Venus also lies close to the Sun but may be glimpsed as a bright dot. It reaches its maximum brightness on 24th.

Mars:  Mars is visible for most of the night, seen against the background stars of Gemini.  

Mars moves into Cancer towards the end of the month.

Jupiter:  The largest planet is a bright object seen high in the sky, between the “horns” of Taurus.. The giant planet is visible all evening, setting around an hour after midnight. The four “Galilean Moons”, two of which are as large or larger than the planet Mercury, are visible even in small telescopes or large binoculars.

Saturn: The ringed planet lies too close to the Sun, this month, but when it does reappear the rings will have opened out enough to make them visible again.

Uranus and Neptune: Uranus is still visible in the constellation of Taurus, below the Pleiades star cluster,  but, sets  a little after 10.30pm.

Meteor shower: April is our first chance of the year to see shooting stars, or more formally meteors.  

The Lyrid meteor shower falls in April.  It appears to come from a point in the sky lying in the direction of the background constellation of Lyra and so is known as the April Lyrids.

Look out for these meteors between April 16th – 25th.  

The peak time falls on the night of 22nd -23rd.  Meteors are the remnants left in the path of comets as they orbit the Sun.  We see them when the Earth passes through a cloud of these remnants.  The April Lyrids are the remnants of Comet Thatcher.

This year the Moon is nearing Full and so its light will drown out all but the brightest meteors. The Lyrid meteors are relatively slow-moving and can include some bright shooting stars.

The First Quarter Moon occurs on April 5th with Full Moon following on 13th. The Last Quarter Moon is then on 21st with New Moon occurring on April 27rd.  The next Last Quarter then falls on May 1st .

Data supplied by Dale Giles, Torbay Astronomical Society

Diary dates

The next meetings of the Torbay Astronomical Society will be held at Torquay Boys Grammar School, Shiphay Manor Drive, TQ2 7EL.  

On April 10th our visiting speaker will be Dr Tim Wetherell who will tell us about “The Ultimate Fate of the Universe” in the Forum lecture theatre.

And on April 24th an observational evening will be held in Room PL4 and the Observatory (weather permitting) when members will be delighted to provide views of the objects discussed in this article.

In the event of bad weather, short talks and videos will be presented alongside informal discussion and an opportunity to get to know the Society.

Both meetings commence informally at 7:00 pm.  

For details contact the secretary TAS on astrosecretary@gmail.com .  Visitors and prospective members especially welcome.