Ireland

What to watch out for in February’s night skies

The Great Nebula in Orion is easily observable as one of the jewels of the winter sky

Orion. Photograph: John Dolan

John Flannery
Sun Jan 31 2021 - 20:00

Two hundred and fifty years ago this month the French astronomer Charles Messier (1730-1817) submitted the first draft of a catalogue that would guarantee him lasting fame.

Now recognised as a list of the sky's showpiece objects, it contains highlights such as the Great Nebula in Orion (designated M42); the Andromeda Galaxy (M31); and the beautiful Pleiades star cluster (M45).

The catalogue grew out of a need to avoid confusion. During his nightly scans of the sky, Messier occasionally stumbled across patches of light masquerading as the comets he was more interested in observing.

Resolving to keep track of these bogus objects, Messier started noting their positions and details.

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The first entry made by Messier in his compilation was in late-August 1758 with the discovery of the Crab Nebula (M1) in Taurus, an expanding debris cloud from a supernova that was recorded as a "guest" star by astronomers in the Orient in 1054 AD. Further finds soon followed.

By February 1771, the list had grown to 45 objects and Messier submitted it to l’Académie des Sciences for publication in their Mémoires.

Two further versions were then printed in 1783 and 1784, with the final tally numbering 103 clusters, nebulae and galaxies that were discovered by Messier and his contemporaries. Since then, researchers have used Messier’s notes to confirm an additional seven entries.

Probably the most famous Messier find lies in the constellation Orion which is almost due south during the early evening in February and is striking in the number of brilliant stars making up the pattern.

The most prominent area is M42, the Great Nebula in the “Sword” that hangs from the Hunter’s Belt which is delineated by three stars in a row. You will notice one of stars in the Sword appears a little fuzzy to the unaided eye.

Train your binoculars on the area and that “star” resolves into a bright patch of light with a grey-green hue, while a telescope reveals delicate tendrils of gas draped across the field of view.

At 1,340 light years away, M42 is the closest star forming region to us. Right at its heart is a very young cluster called the Trapezium whose age is estimated at 300,000 years, and whose members will blow away excess material to emerge from their cocoon in time.

The nebula is illuminated by ultraviolet radiation emitted by the more brilliant cluster stars ionising the surrounding interstellar medium.

Studies by ground-based observatories and the Hubble Space Telescope (HST) have revealed infant suns less than 10,000 years old within M42 which are still hidden within dense dust clouds. Even more intriguing are the proto-planetary disks, or proplyds, that HST photographed.

These are sites of embryo solar systems, some of which are being subject to intense stellar radiation from the Trapezium stars. But, like life, the proplyds are tenacious and despite their pummelling, it looks like they will evolve further in time.

Glancing through Messier's catalogue you will find every class of astrophysical object represented. Many of them are important in modern research because of their prominence, and they are generally amongst the first targets for amateur astronomers as they get started in the hobby.

This time of year, we can trace the lifecycle of a star in the Messier objects and constellations on view. From the stellar nursery of M42, to the young stars of the Pleiades, the last gasps of Betelgeuse and the scattered ashes of the Crab Nebula, that story has been teased out in our pursuit to decipher the secrets of the universe. Messier surely would be in awe of what we have learned in the last 250 years, as we pay homage to his legacy.

The moon this month
Last quarter is on February 4th, new moon on the 11th, and first quarter occurs on the 19th. When we see the first quarter moon it marks where Earth was three and a half hours ago in our orbit round the sun. Conversely, the last quarter moon shows where Earth will be three and a half hours hence. February 27th's full moon can be found in the hindquarters of Leo the Lion.

The planets this month
Mercury continues its evening sky apparition, but it is now rapidly getting lower in the southwest and will be slipping into the solar glare towards the end of the first week of February.

Mercury then swings between us and the sun on February 8th before moving into the morning sky. The innermost planet rises at 6.25am on February 28th and may be seen low in the southeast just as civil twilight commences 15 minutes later.

Venus is too close to the sun to be seen this month from Ireland. It is very near Jupiter on the 11th but that dramatic pairing will probably only be spotted from more southerly latitudes than ours.

Mars can be found in Aries these evenings and is still reasonably bright, despite it receding further from Earth. The Red Planet is not setting until 2am throughout the month and its travels across the celestial sphere carry it across the border into Taurus on the 24th. The moon is near Mars on the evening of February 18th.

Both Jupiter and Saturn are morning sky objects, with the former likely to prove the tougher to spot prior to sunrise. Jupiter rises at 6.40am on the 28th which is the same time as when civil twilight begins that morning.

Saturn precedes Jupiter by about 20 minutes so it may be an easier catch. It is within four degrees of Mercury on the morning of February 23rd but the two are very low.

Spaceflight this month
Mars is centre stage this month for three missions that launched from Earth last July: the UAE's Al-Amal ('Hope'); China's Tianwen-1 ('Heavenly Question'); and NASA's Perseverance. Each have different goals, and comprise instrumentation provided through partnerships with other space agencies and institutions.

The UAE’s Hope mission is the first to arrive on the 9th, with the objective of investigating the martian climate over a period of two years. Mars was a wetter planet billions of years ago but has lost much of its atmosphere over time. The Hope mission, along with the MAVEN probe in orbit since 2014, aim to find out why this has happened.

China's Tiawen-1 initially enters a polar orbit on February 10th from where it will study the martian atmosphere and produce global maps. An onboard rover will then be deployed in early May on to the planet's surface. China will thus become only the second nation to land a rover on Mars, and it will join the currently active Curiosity which landed in 2012, along with this year's Perseverance.

Last to reach the Red Planet is the US Mars 2020 from where it will release the Perseverance rover to land on February 18th in the 49km diameter Jezero crater. The vehicle is designed for astrobiological and geological studies of the area and will cache material for a possible future Mars sample-return mission. Perseverance will also deploy the short-range Ingenuity helicopter drone to explore the immediate environment of the landing site.

John Flannery is a long-time amateur astronomer with an interest in the history and lore of the sky along with astronomical phenomena observable with the unaided eye. He is a member of the Irish Astronomical Society which promotes astronomy outreach.

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