Culture

The Sky Above You – April 2022

By Duncan Lunan

The Moon will be New on April 1st and April 30th..  (Were those Full Moon dates, the latter would be a Blue Moon, the second one of the month.)   The Moon will be Full on April 16th.   On April 30th there will be a partial solar eclipse, visible only from south-west South America and the nearby Pacific.

The planet Mercury is well placed in the April evening sky, after passing the New Moon on the 1st and superior conjunction with the Sun on the 2nd.  Appearing around the 10th, passing Uranus further up the sky on the 17th, Mercury is at greatest elongation from the Sun on the 29th, and is close to the Pleiades that night, on the 30th and on May 1st.  Though growing fainter, it will still be brighter than Aldebaran in Taurus, setting to its left. 

Venus is brilliant in the morning sky through the month.  In early April Saturn and Mars will be nearby in Capricornus, and Venus will be very near Jupiter on April 30th and May 1st.  

Mars rises at 4.40  a.m. in mid-April, in Capricornus, to the right of Venus.  On 5th April Mars passes very close below Saturn, and on April 24th – 27th the waning crescent Moon will pass below Saturn, Mars, Venus and Jupiter, all low down in the twilight and best seen with binoculars. 

Jupiter was not visible in March, but returns to the morning sky around April 7th, in Pisces, in good time for its close encounter with Venus on April 30th.  Neptune is near Jupiter on the 12th

Saturn, also in Capricornus, is very close above Mars on April 5th, and joins the predawn grouping of the planets above for May and June.  Saturn is nearest the Moon on the 24th.

Uranus in Aries is the only planet not taking part, setting around 9.30 p.m. in April, passed by Mercury on the 17th.  Uranus is near the Moon on the 3rd, less than one degree from it, and will pass behind the Moon as seen from southern regions of South America.  Uranus will have disappeared behind the Sun by late April, but more lunar occultations of it will be seen from different parts of the world, later in the year. 

Neptune returns to the morning sky in Pisces, rising about 5.30 a.m. in April, near Jupiter on the 12th, and the Moon and Venus on the 27th.

The Lyrid meteors from Comet Thatcher peak on April 21st – 22nd, with no interference until the Moon rises at 3.30 a.m..

The James Webb Space Telescope

News from NASA about the James Webb Space Telescope continues to be good.  After its successful launch on Christmas Day, over the next month the JWST travelled out to the Sun-Earth L2 point, a million miles beyond Earth on the far side from the Sun, and took up a circular ‘Lissajou’ orbit around it.  It joined the Gaia space telescope, already in L2 orbit, which photographed it at a distance of 600,000 miles on 18th February. 

On the way out all the many components of the telescope had been deployed successfully, and once it was on station at L2, all 18 mirror segments were released from the clamps which held them during launch.  It wasn’t expected that any images could be obtained at that stage, but they were already so close to the final configuration that 18 images of the target star in Ursa Major were obtained at once, out of focus but grouped in a single picture.  Subsequently those multiple images were brought into a hexagonal array and then overlapped, one by one, until a single image was obtained, still blurry, but to be sharpened up in the fourth phase as the 18 segments were focused to function as single mirror.  Phase 5 began on March 11th and the first sharpened image was released on Wednesday March 16th,  switching targets to a star 1,995 light-years away, designated 2MASS J17554042+6551277.  Comparisons with images of it previously taken in a different infrared band by the Spitzer space telescope, and optically by the PanSTAARS telescope on Hawaii, show markedly higher resolution – in fact it’s already at the theoretical limit of resolution, though further improvements can still be made. 

The 2100-second image was made with the telescope’s Near Infra Red Camera  (NIRC), and the Near-Infrared Spectrograph (NIRSpec), Mid-Infrared Instrument (MIRI), and Near InfraRed Imager and Slitless Spectrograph (NIRISS) are now being brought to the same level of accuracy.  Meanwhile the telescope continues to cool down in the shadow of its huge fivefold sunshades, and phase 6 will continue for six weeks, overlapping in its final stages with phase 7.  MIRI will be the last instrument to come on line, requiring a cryogenic cooler to bring it to final operating temperature of minus 448 Fahrenheit, minus 267 Celsius, just 6 degrees above Absolute Zero.  It is still not expected to be operational until July, but everything is going very well so far.

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