Yearbook of Astronomy 2021

By Brian Jones

The annual treasury for sky-watchers and stargazers, including references and a variety of fascinating articles.

The Yearbook of Astronomy series is renowned for its comprehensive jargon-free monthly sky notes and authoritative sky charts that enable backyard astronomers and sky-gazers everywhere to plan their viewing of the year’s eclipses, comets, meteor showers, and minor planets, as well as detailing the phases of the moon and visibility and locations of the planets throughout the year. Every annual edition also includes a variety of entertaining and informative articles. Among the wide-ranging articles in this 2021 edition are:

• Male Family Mentors for Women in Astronomy
• Henrietta Swan Leavitt and Her Work
• Solar Observing
• Obsolete Constellations
• Lunar Volcanism
• Pages From the Past: Collecting Vintage Astronomy Books
• Maori Astronomy in Aotearoa-New Zealand, and more

In addition you’ll find the first in a series entitled Mission to Mars: Countdown to Building a Brave New World, scheduled to appear in the Yearbook throughout the 2020s to keep you fully up to date with the ongoing investigations, research, and preparations that are already underway, as well as those in the planning phase, geared towards sending a manned mission to Mars around the end of the decade. We are at the start of what promises to be an exciting journey—and the Yearbook of Astronomy continues to be an essential companion.

• Language: English
• Publisher: Open Road Integrated Media
• Release date: Oct 31, 2020
• ISBN: 9781526771896

Brian Jones

Specialises in leasehold law and residential property management

Book preview

The Monthly Star Charts

Northern Hemisphere Star Charts

This chart shows stars lying at declinations between +45 and +90 degrees. These constellations are circumpolar for observers in Europe and North America.

Southern Hemisphere Star Charts

This chart shows stars lying at declinations between –45 and –90 degrees. These constellations are circumpolar for observers in Australia and New Zealand.

The Planets in 2021

Lynne Marie Stockman

Mercury is one of the most elusive planets in the sky, never straying far from the Sun and thus never seen in truly dark skies. This year’s best evening apparitions occur in April–June (northern temperate latitudes) and August–October (southern hemisphere). The optimal time to see Mercury in the east before sunrise is February–April for southern observers and October–November in the northern hemisphere. The August–October evening appearance of Mercury may not even be visible to planet watchers in the far north as the planet barely clears the horizon. Mercury has several close encounters with other planets but most of these bodies are near solar conjunction and difficult to see. The tiny planet is occulted by the Moon on 3 November and is also very close to the totally eclipsed Sun a month later on 4 December.

Venus is the morning star as the year begins, low in the east before sunrise and vanishing before superior conjunction in late March. It reappears as the evening star in April in what is an excellent apparition for observers in southern and equatorial latitudes. However, for astronomers in northern temperate regions, 2021 is the ‘Year without Venus’ as the planet struggles to reach much more than 15° in altitude. The brightest planet in the sky is occulted by the Moon in May and November, and passes close by three first-magnitude stars: Regulus (in July), Spica (in September) and Antares (in October). Venus reaches its maximum brightness in December.

Mars has a quiet year, progressing steadily through the constellations Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, and Scorpius before ending up in Ophiuchus. Mars has a long tenure as an evening sky object, beginning the year at magnitude −0.2 before fading to +1.8 by the time it reaches solar conjunction in early October. The red planet reappears in the east in November but remains embedded in the dawn twilight to the end of the year. Mars is occulted by the Moon three times this year, once in April and twice in December. It also passes close by Regulus (α Leonis) in July.

Jupiter begins the year in Capricornus, entering Aquarius in April before returning to Capricornus in August and then ending the year back in Aquarius. Jupiter is always very bright but it will be difficult to see during the first two months of the year as it undergoes solar conjunction in late January. It has several close encounters with Mercury and Venus around the time of conjunction but only the very close approach to Mercury in early March is likely to be easily visible. A morning sky object from February, it passes into the evening sky around June or July, eventually reaching opposition in August. The Moon keeps its distance this year, never approaching nearer than 3.3° but Jupiter does pass very close to fourth-magnitude star Theta (θ) Capricorni in February.

Saturn occupies the unremarkable constellation of Capricornus for the entire year. At conjunction with the Sun in late January, the ringed planet is not easily seen until toward the end of February when it appears in the dawn sky ahead of sunrise. It slowly pulls ahead of the Sun, reaching opposition in August. It is then visible in the evening sky until the end of the year. Saturn is approaching a ring plane crossing event in 2025 so the tilt of the rings is slowly decreasing. The rings are at their most open at the beginning of the year, closing down to a tilt of just under 17° in May before opening up slightly again. The Moon gets no closer than 3.2° to the planet this year; fourth-magnitude Theta (θ) Capricorni is the brightest star in close proximity (in May).

Uranus inhabits the dim constellation of Aries throughout 2021. It begins the year in the evening sky, vanishing in early April before reaching conjunction at the end of the month. It reappears in the east before dawn the following month, rising ever earlier and passing into the evening sky by July (northern hemisphere) or August (southern hemisphere). Opposition takes place in early November. The Moon makes a series of close passes by the planet, beginning over 3° away in January and coming to within 1.3° in October before moving away again. Sixth-magnitude Omicron (ο) Arietis is the brightest star near the path of Uranus this year; the green ice giant passes by it mid-October whilst in retrograde.

Neptune spends the entirety of 2021 in the watery constellation of Aquarius. It is an evening sky object at the beginning of the year but vanishes in the glow of sunset by early to mid-February. Conjunction occurs in March and the eighth-magnitude planet reappears in the morning sky in April. It is best seen from southern latitudes during the middle part of the year and from the northern hemisphere at the beginning and end of the year. Opposition occurs in September. The most distant planet in the solar system does not pass by any bright stars this year and the Moon never gets closer than 4°.

Phases of the Moon in 2021

Eclipses in 2021

There are a minimum of four eclipses in any one calendar year, comprising two solar eclipses and two lunar eclipses. Most years have only four, as is the case with 2021, although it is possible to have five, six or even seven eclipses during the course of a year.

On 26 May there will be a total lunar eclipse which will be visible across the Pacific Ocean and regions of southern and eastern Asia, Japan, Australia and the western United States. The eclipse commences when the Moon enters the Earth’s penumbra (partial shadow) at 08:48 UT and ends at 13:50 UT. The Moon begins to enter the Earth’s umbra (full shadow) at 09:45 UT, with full eclipse lasting from 11:11 UT to 11:26 UT and maximum eclipse occurring at 11:20 UT. The Moon leaves the umbra at 12:52 UT.

An annular solar eclipse will take place on 10 June. The path of this eclipse will be restricted to the eastern tip of Russia, the Arctic Ocean, western Greenland and north eastern Canada. The partial eclipse will be observable from the north eastern regions of the United States, northern Europe and most of Russia. The eclipse commences at 08:12 UT and ends at 13:11 UT. Full eclipse will last from 09:50 UT to 11:34 UT with maximum eclipse at 10:42 UT.

There will be a partial lunar eclipse on 19 November which will be visible throughout most of eastern Russia, Japan, the Pacific Ocean, North America, Mexico, Central America, most of Australia and western South America. The eclipse commences at 06:02 UT and ends at 12:04 UT with the full eclipse lasting from 07:19 UT to 10:47 UT. Maximum eclipse occurs at 09:03 UT, when the Moon will be almost entirely immersed in the Earth’s umbra, with only a thin sliver remaining outside this zone.

The path of totality of the total solar eclipse of 4 December will be confined to Antarctica and the southern Atlantic Ocean, although a small partial eclipse will be observable from most parts of South Africa. Observers located in Tasmania, and at various locations along the southern Australian coast, will see the partial phase as the sun sets. The eclipse begins at 05:29 UT and ends at 09:37 UT with total eclipse taking place between 07:00 UT and 08:06 UT and maximum eclipse at 07:33 UT.

Some Events in 2021

The entries for meteor showers state the date of peak shower activity (maximum). The figure quoted in parentheses in column 4 alongside each meteor shower entry is the expected Zenith Hourly Rate (ZHR) for that particular shower at maximum. For a more detailed explanation of ZHR, and for further details of the individual meteor showers listed here, please refer to the article Meteor Showers in 2021 located elsewhere in this volume. For more on each of the eclipses occurring during the year, please refer to the information given in Eclipses in 2021.

Monthly Sky Notes and Articles

Morning Apparition of Venus

June 2020 to March 2021

January

New Moon: 13 January

Full Moon: 28 January

MERCURY is visible in the west soon after sunset, with northern vantage points favoured over the southern hemisphere. Its brightness spans two magnitudes, beginning the month at −1.0 and ending at +1.1. The tiny planet is 1.6° south of Saturn on 10 January and 1.4° south of Jupiter the following day but both events will be tricky to observe as all three planets are only about 13° away from the Sun at the time. The nearly New Moon passes 2.3° south of Mercury on 14 January; under perfect seeing conditions sharp-eyed planet watchers may spot it. Mercury reaches greatest elongation east (18.6°) on 24 January and enters into retrograde motion on the penultimate day of the