Tower and Town, March 2023 (view the full edition)Happy New Astronomical Year!
Known as the first point of Aries (and fixing the zodiac constellation areas), due to the complex phenomenon of precession (wobble of the earth's rotation axis) over the last 2000 years since naming, it now falls (i.e. the sun is in front of) the constellation Pisces! Most know this day as one of equal day and equal night length but more importantly it is a day for navigation and alignments, as one of the only two days in the year that the sun rises due east and sets due west. Every day after the Spring Equinox, the sun rises further and further north on the eastern horizon, until it reaches its maximum 'standstill' position, some 40 degrees north of east on June 21st. On 20th March, the sun reaches 39 degrees altitude above the southern horizon here in Marlborough (90 degrees minus our latitude) at local noon. The Spring Equinox is of course also significant in the Christian year (as in many world religions) as it fixes the day for Easter: Easter Day must fall on the first Sunday after the first full moon after the Vernal Equinox. So, if the weather allows either sunrise or sunset to be visible, go out on 20th March and note the directions of true east and west from where you are, as we all look forward to longer summer evenings. Charles Barclay (FRAS) is a professional outreach astronomer and was director of the Blackett Observatory 1997-2022. Charles Barclay |
The astronomical year begins on the Vernal (Spring) Equinox; this year the day falls on Monday 20th March. Just before 9.30pm the sun reaches the origin of the celestial coordinate system (equivalent to longitude and latitude, but on the sky). The sun crosses the celestial equator into the northern hemisphere of the sky and officially starts our northern hemisphere summer season. Arguably the most important day of the year and one of the quarter days (with the solstices) that have divided the year from ancient times (and may well account for the otherwise strange start of the tax year today) from which many astronomical measurements are taken.