Venus meets Pleiades as Comet ATLAS keeps us guessing

Alan Pickup

Author: Alan Pickup
The maps show the sky at midnight BST on the 1st, 23:00 on the 16th and 22:00 on 30th. Arrows shows the motions of Venus and Comet ATLAS.

In flagrant disregard for the rules of social distancing, the dazzling evening star Venus passes very close to the Pleiades, or Seven Sisters, star cluster in the first few days of April. Three other naked eye planets have congregated low down in our predawn sky while astronomers are keeping a close eye on Comet ATLAS which may become spectacular during May, or perhaps fizzle entirely.

Venus stands 38° above Edinburgh’s western horizon at sunset on the 1st and sinks to set in the north-west at 00:56 BST. Blazing at magnitude -4.4, second only to the Moon in nighttime brilliance, it lies 2° or four Moon-breadths below the Pleiades on the 1st. By the 3rd, it sits only 0.3° below-left of the cluster’s brightest star, Alcyone, in the closest conjunction between Venus and the Pleiades in our lifetimes. The meeting should make for a superb sight through small telescopes and binoculars and provides an ideal opportunity to test our astrophotography skills.

Venus’ motion continues through Taurus to within 4° of the star Elnath, the tip of the Bull’s northern horn, at the month’s end. By then, Venus has fallen to 30° altitude at sunset and reached its greatest brilliancy (magnitude -4.5) as it swings closer to us around the near side of its orbit. Its distance decreases this month from 98 million to 64 million km, while, viewed telescopically, it swells from 25 to 39 arcseconds and the sunlit proportion changes from 47% to 25%. By late April its crescent form should be apparent through binoculars.

Look in the west-north-west at nightfall on the 25th for the earthlit crescent Moon when it lies below Venus, to the right of Taurus’ leading star Aldebaran and to the left of the Pleiades.

The Sun climbs more than 10° northwards during April as sunrise/sunset times for Edinburgh change from 06:42/19:52 BST on the 1st to 05:30/20:51 on the 30th. The Moon is at first quarter on the 1st and full on the 8th which, because it occurs nine hours after the Moon is at its closest for the year, qualifies as a so-called supermoon. As such it is about 15% larger and brighter than an average full Moon though you might be hard-pressed to notice the difference. The Moon is at last quarter on the 14th, new on the 23rd and at first quarter again on the 30th.

Orion is leaning over in the south-west at nightfall at present but has all but set in the west by our star map times. Betelgeuse, the red supergiant at Orion’s shoulder, appears to be recovering well after its surprisingly deep fade over recent months. It is now comparable with Aldebaran in brightness and more than twice as bright as it was in February. Good evidence has emerged that the dimming occurred after it ejected material from its surface which then condensed into an obscuring cloud of dust.

Our maps show the Plough in the zenith as Leo leads Virgo from the south to the south-west. Catch the Moon above Regulus in Leo on the 4th and above Spica in Virgo on the 7th-8th.

Comet ATLAS, discovered by the ATLAS survey from Hawaii at the end of last year, appears to be following an extremely elliptical orbit around the Sun in a period of around 6,000 years. As it approaches perihelion, its closest to the Sun (38 million km) on May 31, it has brightened more sharply than expected. Current forecasts of its peak magnitude range all the way from magnitude 2 to -11, the latter making it one of the brightest comets on record. Its path suggests that it may be a sibling of the Great Comet of 1844, perhaps after their parent comet split during a previous return to the Sun.

Some astronomers suspect that it may crumble and disappear as it nears perihelion, but if it survives it could become an impressive sight during May. It begins April as a binocular object of the seventh or eighth magnitude, appearing as a greenish blob with an upwards pointing short tail in photographs. As it moves through the dim constellation of Camelopardalis, between Auriga and Polaris (see map) it may brighten to naked eye visibility later in the month. Try searching on the Internet for a better chart than I can provide here.

Mercury remains hidden in the Sun’s glare before dawn as Jupiter, Saturn and Mars stand very low down in our south-eastern sky. Jupiter, the furthest west (right) of the trio, is conspicuous at magnitude -2.1 to -2.3 as it creeps eastwards in Sagittarius. Saturn is fainter at magnitude 0.7 in Capricornus where it is 6° to the left of Jupiter. Mars improves from magnitude 0.8 to 0.4 as it speeds from only 1° below Saturn on the 1st to lie 19° left of Saturn on the 30th. Although all three are below 10° in altitude in Scotland’s morning twilight, they reach high up in the east for observers in the southern hemisphere.

Meteor watchers may care to watch for medium-swift meteors of the Lyrids shower which lasts from the 14th to the 30th and is expected to peak under moonless (and, hopefully, clear) skies on the morning of the 22nd. The meteors, some of them very bright, diverge from a spot that lies to the right of Vega in Lyra as it climbs in the east following our map times. Large numbers of meteors are not expected, though there have been fine displays in the past, the last in 1982. Its meteoroids were released from Comet Thatcher which follows a 415-year orbit of the Sun and was last seen in 1861.

Diary for 2020 April

Times are BST

  • 1st 11h First quarter
  • 3rd 08h Moon 1.6° N of Praesepe
  • 3rd 21h Venus 0.3° S of Pleiades
  • 4th 20h Moon 4° N of Regulus
  • 8th 04h Full moon (supermoon)
  • 8th 08h Moon 7° N of Spica
  • 11th 13h Moon 7° N of Antares
  • 15th 00h Moon at last quarter and 2.0° S of Jupiter
  • 15th 10h Moon 2.5° S of Saturn
  • 16th 06h Moon 2.0° S of Mars
  • 22nd 01h Peak of Lyrids meteor shower
  • 23rd 03h New moon
  • 25th 06h Moon 7° S of Pleiades
  • 26th 05h Moon 4° N of Aldebaran
  • 26th 10h Uranus in conjunction with Sun
  • 26th 16h Moon 6° S of Venus
  • 30th 15h Moon 1.9° N of Praesepe
  • 30th 22h First quarter

This is an extended version, with added diary, of Alan’s article published in The Scotsman on 31 March 2020, with thanks to the newspaper for permission to republish here.