The iconic Arecibo Telescope at the National Astronomy and Ionosphere Center (NAIC) in Arecibo, Puerto Rico, as it used to be

2020 isn't likely to have been anybody's favorite year, yet there have been a lot of exciting happenings in astronomy. It wasn't easy to choose, but here are my top ten stories.

Historic observatories
September saw two historic observatories, Lick and Mount Wilson, survive close encounters with California wildfires. But sadly, in December, old age was not so kind to the Arecibo Telescope in Puerto Rico. Arecibo's 300-meter dish was built in a natural sinkhole. It had been the world's largest radio telescope for over fifty years until the Chinese FAST telescope was completed in 2016. On December 1st several suspension cables failed, causing a 900-ton platform to crash into the dish, wrecking it beyond repair. Its loss was deeply felt by the astronomical community and many Puerto Ricans.

Black holes, Nobel Prizes
There was good news for astronomy from the Swedish Academy of Sciences in October. The Nobel Prize for physics was shared by three people who've helped to revolutionize our understanding of black holes. Roger Penrose approached the subject mathematically and philosophically, while Andrea Ghez and Reinhard Genzel have both carried out decades of observations of the stars in the center of the Galaxy. The motions of these stars provided evidence of a supermassive central black hole.

Keeping an eye on the Sun
Our Sun isn't just of academic interest to us, but is essential to our survival. In February, the European Space Agency (ESA) launched its Solar Orbiter, saying that it “is the most complex scientific laboratory ever to have been sent to the Sun. Although our life-giving star has been an object of scientific interest for centuries, its behaviour still presents a puzzle.” The probe has a heat shield that can withstand temperatures of 520 °C (970 °F).

Exciting exoplanet discovery
The holy grail of exoplanet discoveries is an Earth-sized planet in the habitable zone of its star. The habitable zone is the area around a star in which surface water could exist. NASA's latest planet hunter TESS (Transiting Exoplanet Survey Satellite) has discovered the first such planet. TOI 700 d has a radius and mass similar to that of Earth and it orbits in the habitable zone of its red dwarf star.

Gaia
ESA's Gaia mission was launched in December 2013. In December 2020, the third data set was released. It's providing the most detailed map of the Milky Way ever undertaken. There are high-precision measurements of nearly 1.7 billion stars and many other celestial objects, providing coordinates, distances and velocities. Astronomers are delighted.

Off to Mars
Although Elon Musk is not yet on his way to Mars, three missions were launched to the red planet in July. (1) NASA's Perseverance rover is the latest of its Martian missions. (2) China, which has become a major player in the space exploration game, launched Tianwen-1. This is its first Mars mission, and it comprises an orbiter and a rover. (3) The third mission – an orbiter – is from a complete newcomer to deep space missions. Launched from Japan's Tanegashima Space Centre for the United Arab Emirates (UAE), it's the Arab world's first planetary mission. It's called Al-Amal (Hope). All three missions are expected to arrive in 2021.

Sample collectors
Three spacecraft acquired samples from other Solar System bodies and then headed home to Earth.

Asteroids
NASA's Osiris-Rex mission to asteroid Bennu obtained its samples this year and is due back in September 2023. Japan's Hayabusa2 studied asteroid Ryugu, collected its samples in February 2019, and brought the samples safely to Earth in December 2020. Both Bennu and Ryugu are listed as “potentially hazardous” asteroids.

Back to the Moon
The third spacecraft was China's Chang'e 5. It was launched on the November 23, and on December 1 it touched down on the Moon in the Oceanus Procellarum (Ocean of Storms). The samples were returned on December 16. This was the first lunar sample-return mission since the Soviet Union's Luna 24 in 1976.

A distant visitor
Comet NEOWISE was discovered in March, and in July it delighted astronomers and the general public. Bright and beautiful, it was visible even to the naked eye, but much enhanced if viewed with binoculars. After surviving its trip around the Sun, the comet's tail was an elegant feature as it headed towards the outer solar system. It'll be back again in about 6800 years.

The Great Conjunction
The big sky event of the year was the Great Conjunction on the night of the northern winter solstice, December 21. In a conjunction, two (or more) heavenly bodies appear to be close together in the sky. Jupiter and Saturn moved closer and closer together in 2020. On the evening of the solstice, the separation was so small that they looked like one body. The two planets are in conjunction every twenty years, but this was closest one in over 400 years.

Image credits:
Comet NEOWISE: Aleksandr Yuferev, South-Western Siberia, near Novosibirsk, Russia (Sky & Telescope)