Three-tailed green comet closest to Earth as month begins

Alan Pickup

Author: Alan Pickup

The maps show the sky at 22:00 GMT on the 1st, 21:00 on the 15th and 20:00 on the 28th. Arrows show the motions of Mars and Comet ZTF

Venture outside on any clear February evening to be confronted with a breathtaking night sky and, if we don’t wait too long, three conspicuous planets. There is the added bonus of our brightest comet since Comet NEOWISE in the summer of 2020, though Comet ZTF, or Comet 2022 E3 (ZTF) to award it its proper title, is certainly more of a challenge.

The brightest of those planets is Venus which blazes in the south-west at nightfall, sinking to set at Edinburgh’s western horizon at 19:05 on the 1st and as late as 20:44 on the 28th. Above and to its left stands the conspicuous Jupiter, the gap between them destined to shrink from 30° at present to only 1.5°, three Moon breadths, by the 28th.

Mars, much higher in our southern evening sky, was noticeable to the right of the gibbous Moon on 31 January and will be in much the same relative position on the 28 February, one lunation later. In the meantime, Mars tracks 9° eastwards (to the left) against the stars of Taurus, moving away from the Pleiades star cluster and passing 8° north of Aldebaran.

The Red Planet, its distinctive rusty hue more obvious through binoculars, is receding following its opposition on 8 December, its distance growing from 131 million to 171 million km and its magnitude falling from -0.3 to +0.4. Telescopes show its small ochre disk shrinking from 10.7 to 8.2 arcseconds, making it harder still to spy any surface markings.

Below Mars and Taurus is the sparkling form of Orion with its contrasting leading stars Betelgeuse and Rigel. Look for the constellation of the Hunter in the south-east as darkness falls and due south one hour before our map times. Above and to its left is Gemini with the Twins, Castor and Pollux, while below-left, and in line with Orion’s Belt, is Sirius.

All Orion’s bright stars are billions of years younger than the 4.6 billion years of our Sun, and its region of the sky is peppered with nebulae (Latin for “clouds”) containing clusters of new-born stars and, most clearly in the case of the Orion Nebula, places where new stars are coalescing before our eyes.

Our southern chart plots the Orion Nebula below the Belt and also two clusters of relatively young stars. M35 is visible through binoculars at the feet of Gemini while M41 sits 4° due south of Sirius and a shade more difficult given its lower latitude in the sky. Both are less than 200 million years old and each covers an area as wide as the Moon.

Comet C/2022 E3 (ZTF) by Pat Devine

Comet ZTF was just brighter than the 6th magnitude when I observed it in late January, with its head, or coma, half as wide as the Moon and visible to the unaided eye from the darkest locations. However, it is far from being the spectacular object that some reports have claimed, and most of us are unlikely to glimpse its faint smudge without, at least, binoculars.

Photographs, though, show the coma as a striking green, the glow emitted when the Sun’s ultraviolet radiation breaks up short-lived molecules of diatomic carbon released from ZTF’s icy nucleus. Recent images also reveal that ZTF sports no less than three tails. One, a long but narrow bluish banner of ionized gas, is being carried directly away from the Sun by the solar wind, while a stubby white tail of dust lies at an angle and a fainter so-called anti-tail pointing towards the Sun represents the dust falling behind in its orbit.

Comet C/2022 E3 (ZTF) by Ian Smith showing solar wind disruption in the tail

That orbit brings it closest to the Earth, 42 million km, on 1 February as it moves outwards from the Sun, so we must expect Comet ZTF to be at its brightest then. Our maps plot it 19° directly above Polaris in the north on the 1st from where it speeds southwards to pass 1.5° west of Capella at midnight on the 5th-6th, and lie similar distances north-west of Mars five nights later and east of Aldebaran on the 14th-15th. The comet last visited the Sun some 50,000 years ago, during the Stone Age, but will never be seen again.

Edinburgh’s sunrise/sunset times change from 08:08/16:45 on the 1st to 07:07/17:44 on the 28th. Full Moon on the 5th is followed by last quarter on the 13th, new on the 20th and first quarter on the 27th.

As Venus pulls slowly away from the Sun’s far side, its dazzling disk appears small through a telescope, around 11 arcseconds in diameter and 90% illuminated. At magnitude -3.9, improving to -4.0, it outshines every other object in our night sky, bar the Moon. The farthest and faintest planet, Neptune, passes a mere 45 arcseconds from Venus on the 15th but, at magnitude 8.0, is 60,000 times fainter and barely visible through binoculars.

Jupiter dims only slightly from magnitude -2.2 to -2.1, so it remains brighter than Sirius while telescopes show it spanning 35 arcseconds at mid-month. As Jupiter converges with Venus, look for the slender earthlit young Moon 3.5° below Jupiter and 5° above-left of Venus on the 22nd.

Jupiter and the 4 Galilean satellites by Radim Stano (4/7/2021)

Jupiter’s four Galilean moons are also best seen telescopically and are the target for the European Space Agency’s Jupiter Icy Moons Explorer probe which arrives in French Guiana this month prior to its launch in a window that opens on 5 April. Following three energy-boosting flybys of the Earth, and one of Venus, it is due to reach Jupiter in 2031 and devote more than two years to studying its three largest moons, all of which may have oceans of water beneath their crusts, and, just possibly, life. Incidentally, the discoveries of a further nine Jovian moons, all 1-2 km wide, have been announced already this year, bringing the total to 91 and surpassing Saturn’s tally of 83.

Saturn, itself, reaches conjunction on the Sun’s far side on the 16th while Mercury is surely too low to spot in Scotland’s bright south-eastern morning twilight over the next few days.

Diary for 2023 February

M44 Praesepe by Nigel Goodman

  • 3rd 20h Moon 1.9° S of Pollux
  • 4th 22h Moon 4°N of Praesepe
  • 5th 07h Mars 8° N of Aldebaran
  • 5th 18h Full Moon
  • 6th 01h Comet ZTF 1.5° W of Capella
  • 6th 18h Moon 4° N of Regulus
  • 11th 05h Moon 4° N of Spica
  • 11th 12h Comet ZTF 0.9° E of Mars
  • 13th 16h Last quarter
  • 14th 19h Moon 1.8° N of Antares
  • 15th 01h Comet ZTF 1.5° E of Aldebaran
  • 15th 12h Venus 0.01° S of Neptune

    M45 Pleiades by Pat Devine

  • 16th 17h Saturn in conjunction with Sun
  • 20th 07h New Moon
  • 22nd 08h Moon 2.1° S of Venus
  • 22nd 22h Moon 1.2° S of Jupiter
  • 26th 15h Moon 2.1° S of Pleiades
  • 27th 08h First quarter
  • 27th 14h Moon 9° N of Aldebaran
  • 28th 04h Moon 1.1° N of Mars

This is an extended version, with added diary, of Alan’s article published in The Scotsman on 31 January 2023, with thanks to the newspaper for permission to republish here.