Beginning of Spring 2021

Table of Contents

1. The beginning of spring2 2. Eclipses and related phenomena3 3. Night sky observation in spring4 4. Astronomical almanac4 5. Daylight saving time4

______© Instituto Geográfico Nacional c/ General Ibáñez Ibero 3. 28003 - Madrid – España 1

1. The beginning of spring

Spring 2021 will begin on March 20 at 10:37 official Madrid time, according to calculations by the Observatorio Astronómico Nacional (Instituto Geográfico Nacional - Ministerio de Transportes, Movilidad y Agenda Urbana). This season will last 92 days and 18 hours, and will end on June 21 with the beginning of summer.

During this season, the sky at dawn will be dominated by Jupiter and Saturn. Mars will be visible at dusk, and will be joined by Venus in late April and Mercury during the month of May. On May 26 there will be a total lunar eclipse that will be visible from East Asia, Australia, the Pacific and America. And on June 10, there will be an annular solar eclipse that will be visible from North America, Europe and Asia. This solar eclipse will be visible from Spain as a partial one.

The beginning of the seasons is set, by definition, by the moment when the Earth is in certain positions in its orbit around the Sun. In the case of spring, this position takes place when the center of the Sun, seen from the Earth, crosses the celestial equator in its apparent movement towards the north. The day when this happens, the length of the day and the night practically coincide. This circumstance is also known as the spring equinox. At the moment when spring begins in the northern hemisphere, autumn begins in the southern hemisphere.

Possible dates for the beginning of spring. Throughout the 21st century, the beginning of spring can occur, at most, in three different dates of the calendar (from March 19 to 21). The earliest start is in 2096 and the latest start takes place in 2003. The variations from one year to another are due to the way the sequence of calendar years (some leap years, others not) fits with the duration of the orbit of the Earth around the Sun (a period known as tropical year).

Duration of the day. The beginning of spring is the time of the year when the length of the day becomes longer the quickest. At the latitude of the Iberian Peninsula, each day the Sun rises more than a minute earlier than the day before, and in the evening it sets more than a minute later each day. Thus, at the beginning of spring, the time that the Sun spends above the horizon increases by almost three minutes each day.

Solar activity. The Sun's activity is characterized by the presence of sunspots, flares and prominences on its surface, and from Earth, it can affect the propagation of radio waves and results in a greater presence of polar auroras. This solar activity follows a period of approximately 11 years, and is associated with the Sun's magnetic cycle. We are currently in the 25th solar cycle which began in December 2019 and is predicted to peak in July 2025. According to estimates made by NOAA and the Space Weather Prediction Center, during spring the number of sunspots will reach values between 21 and 47. Plots with the number of sunspots in recent years and predictions of the evolution for the 25th cycle can be found at: http://www.swpc.noaa.gov/products/solar-cycle-progression

______© Instituto Geográfico Nacional c/ General Ibáñez Ibero 3. 28003 - Madrid – España 2

2. Eclipses and related phenomena

On May 26, a total lunar eclipse will be visible from East Asia, Australia, the Pacific Ocean and America. This eclipse will not be visible from Spain. More information: https://www.ign.es/web/resources/astronomia/pdf/eclipses2021/2021may26-E.pdf

On June 10, there will be an annular solar eclipse that will be visible as partial in North America, Europe and Asia. The annularity will be visible from northeastern Canada, Greenland (Denmark) and northeastern Russia. This eclipse will be visible from Spain as partial. More information at: https://www.ign.es/web/resources/astronomia/pdf/eclipses2021/2021jun10-E.pdf

3. Night sky observation in spring

At any time of the year there are astronomical phenomena of interest, either predicted (such as eclipses) or not (such as new comets). It is usually preferable to carry out the observations on dates close to the New Moon (April 12, May 11 and June 10), except when we aim to observe the Moon itself.

Full Moon. The first Full Moon of summer will take place on March 28, while the subsequent Full Moons will be spaced by periods of 29 or 30 days. This spring, two Full Moons will take place: April 27 and May 26.

Visibility of the planets. At dawn, Jupiter and Saturn will be visible throughout spring. At dusk, Mars will be visible throughout the season, while Mercury will only be visible in May and, from late April onwards, Venus will appear in the evening sky.

Meteor showers. Without a telescope, occasional meteor showers can be observed. The two most important meteor showers of spring are the Lyrids, with a maximum around April 22, and the eta Aquarids, with a maximum on May 6. More information at: https://astronomia.ign.es/web/guest/lluvias-de-meteoros

Constellations. As for the fictitious groups of stars known as constellations, spring is a good time to observe them, as the nights are still long and it is less cold than in winter. One of the most typical constellations in spring is Leo, which is easy to locate southwards after sunset because of its inverted question mark shape. Looking north of Leo, we find the also easily recognizable Ursa Major. To the east of Leo, the constellations Virgo and Bootes stand out, each with a bright star: Spica in Virgo and Arcturus in Bootes. The triangle formed by these two stars and by Regulus in Leo is known as the spring triangle, and its location in the sky provides a good starting point to begin exploring the rest of the constellations visible during the season.

Observations with binoculars or small telescopes. With large binoculars or a small telescope, equipped with an appropriate lunar filter, the relief of the Moon can be observed. In order to have a good insight, it is recommendable to observe the Moon night after night while the phase increases, because with this strategy new orographic accidents will be perceived each day. When the night is darker because of the New Moon, you can try to see emission nebulae such as the Orion nebula complex (Messier 42 and 43), the Pleiades group of stars and the supernova remnant known as the Crab nebula (Messier 1). With binoculars you can also see the brightest moons of Jupiter and take a tour at the starry band that makes up the Milky Way.

4. Astronomical Almanac

For more information on the astronomical phenomena of the year, you can consult the book published yearly by the Instituto Geográfico Nacional (Anuario Astronómico).

5. Daylight saving time

As usual, daylight saving time starts on the last Sunday of March. At 2 a.m. Spanish mainland time on Sunday 28 March we will set the clock forward to 3 a.m. (in the Canary Islands, at 1 a.m. clocks will be set to 2 a.m.). That day will therefore officially be one hour shorter.

At the moment, the European Parliament is discussing the possibility of eliminating time changes from 2021 onwards. There is no firm decision yet, but it is very possible that in the near future the European Union will not change the time again in spring and autumn.

Information provided by the Observatorio Astronómico Nacional (IGN, Ministerio de Transportes, Movilidad y Agenda Urbana). Reproduction authorized provided that the source is acknowledged.