Innehållsförteckning för April 2023 från BBC Sky at Night

Decades in the planning, ESA's Jupiter Icy Moons Explorer (JUICE for short) is scheduled for launch this April. It's the first of Europe's three planned L-class missions, the largest and most costly class of campaign in Europe's long-term plan for space exploration. We're excited to be covering the mission on page 28, where Will Gater explores the spacecraft and its science goals, which include investigating whether conditions could be favourable for life under the thick ice crusts of Callisto, Ganymede and Europa. Jupiter isn't visible in April (it's hidden in the Sun's glare), but for planetary observers it's all about Mercury this month. An elusive world that stays close to our central star in the sky, this month sees it reach its furthest distance from the Sun, setting two hours…

Visit www.skyatnightmagazine.com/bonus-content/9BN84GZ to access this month's selection of exclusive Bonus Content APRIL HIGHLIGHTS Black holes and bending spacetime Luciano Rezzolla discusses the mind-blowing properties of gravity and his quest to understand black holes Download automated telescope software Slew your telescope instantly to each target in this month's Deep-Sky Tour with our selection of automated software. Access extra observing materials Download and print out forms that you can use to sketch and record your planetary observations throughout 2023. The Virtual Planetarium Pete Lawrence and Paul Abel guide us through the best sights to see in the night sky this month.…

Earth 2.0? An Earth-mass planet around red dwarf Wolf 1069 could be a new hot spot in the hunt for extraterrestrial life. The planet takes 15.6 days to orbit its star, meaning that if the planet has formed an atmosphere the surface temperature would be a habitable 13°C, temperate enough for liquid water to pool on the surface. Jupiter rules again Twelve additional moons have been discovered around Jupiter, bringing its tally to 92. The moons are only 1-3km in size, but their discovery puts Jupiter back on top of the moon leader board after it was usurped in 2019 when a similar find brought Saturn's total to 83. Turn to page 28 to read more about JUICE's exploration of Jupiter's largest moons. Damp squib supernova Binary star system CPD-29…

On the 11 April 1981 episode of The Sky at Night, Patrick Moore looked towards the moons of Saturn. The previous November, Voyager 1 had given humanity its first close-up look at these frozen worlds, and the show aired just as NASA had begun to publish maps created from its images. Voyager 1 captured the surfaces of Tethys, Mimas, Rhea, Dioneand Enceladus. As most of the moons were imaged from over 100,000km away, only major features were obvious, but they did reveal a large crater on Mimas (giving it a striking resemblance to the Death Star from Star Wars). Fortunately, Voyager 2 would be able to give them alla second look when it arrived in the system that August. Voyager 1 did pass much closer to one other moon –…

Email your queries to scopedoctor@skyatnightmagazine.com In the sub-zero weather this winter, my 8-inch Go-To Schmidt-Cassegrain telescope won't move vertically to align on a star, though I can power it up and move it horizontally. Can you help? GARY WALKER As the temperature decreases, the viscosity of the lubrication in the gears and bearings of many mounts will start to increase, causing a greater load on the motor drive and even initiating a motor stall if it is cold enough. This could affect either or both axes. If you are using batteries to power your mount, the electrochemical reaction that produces the electric current will slow down with decreasing temperature, reducing the power of the battery, sometimes to below the minimum required for full operation of the mount. Very low temperatures…

There are only a few spots in our Solar System where large bodies of liquid water are either present or strongly suspected: Earth itself, and the interiors of some of the icy moons of the gas giants. Where there's liquid water on our own planet we almost always find lifeforms, and so the faraway oceans of the icy moons have become sites of immense interest in the search for life beyond our own world. Among the forces thought to be heating the insides of Jupiter's largest moons is the gravitational push and pull between themselves as well as with the giant planet – a process that warms them through friction. In the case of the icy moons, this heating is likely to be what is keeping their interior oceans liquid…

Mercury is the smallest planet, barely larger than our own Moon at a mere 2,440km in diameter, As it's also the closest to the Sun, you'd be forgiven for thinking it's the hottest planet in the system, but that's not the case due to a thin ‘exosphere’ of oxygen, Hydrogen, sodiitm, helium and-potassium. Lack of heat retention means its surf ace temperature varies from alrpost 450°C in the day to –108°C at night. Despite being further away, Venus reaches temperatures. up to 470°C thanks to its thick atmosphere. Mercury is a ‘terrestrial’ or rocky planet, displaying a cratered surface that resembles Earth's Moon. Underneath lies a large. metallic core, mantle and crust. Thankd to a minor axial tilt (2°), Mercury doesn't experience seasons. To date, tow NASA missions have visited…

Venus will appear near the beautiful Pleiades open cluster this month. This is conveniently placed and timed in the evening sky. Closest approach is on 10 April, but the approach and separation can be seen on the days before and after this. If it's clear, head outside and suggest making a drawing of the encounter based on what can be seen with the naked eye. The Pleiades are also known as the Seven Sisters, so use this opportunity to ask how many of the cluster stars you can see. www.bbc.co.uk/cbeebies/shows/stargazing…

Venus passes south of the Pleiades during April, creating an opportunity to take a stunning photograph of the bright planet and beautiful open cluster. The best time to see the passage is on the evenings of 8-14 April. Their closest approach occurs on the evenings of 10 and 11 April, when Venus passes 2.7° south of the cluster's centre. Although the evening twilight expands rapidly throughout April, it should still be possible to see the closest part of this encounter against dark skies, the pair appearing over 10° above the westnorthwest horizon. Compromised by twilight, the Pleiades is visited by a thin waxing crescent Moon on the evenings of 21 and 22 April. On 21 April, the 3%-lit waxing crescent Moon sits 8.7° below and slightly to the right of…

Multi-band filters can be used with most astro cameras on the market and are very easy to get to grips with. Lots of telescopes have a filter holder inside the focuser, where the filters are fitted. If this is not available, a filter drawer is a good addition to make life easier. Filters can then be mounted inside and placed in the imaging train near the camera. Extra drawers can be purchased for other filters, making it simple to change them when needed. Dust and notation are problems we have when changing filters manually, for example if you have multiple filters for different objects. A filter wheel is the simplest solution. All the filters can be loaded inside and then in capture-control software each filter can me individually selected. The…

VITAL STATS Serif's Affinity Photo software was released in 2015 and has since been regularly updated with new features. Several useful astrophotography tools were added in 2021, including image stacking, star alignment, and background and gradient removal. Version 2, which we're looking at here, is the latest big upgrade and was released in November 2022. With ease of use and an extremely affordable price, it will certainly entice many astrophotographers desiring a single package that does image sub-stacking and post-processing, and that won't break the bank. We liked Affinity Photo 2's one-off payment user licence model, not locking you into paying a longterm, monthly subscription. There are licences for PC, Mac and iPad, plus a Universal Licence that allows the full Affinity Suite…

How did you select the book's topics? I picked topics that were important but which also had something interesting and fun to write about. Global warming is important. But it was interesting for me because I got to write about Eunice Foote, who in 1856 discovered that carbon dioxide traps heat and was the first person in history to speculate that the climate would change if the amount of that gas in the atmosphere changed. She's been written out of history. Which topic do we know least about? The standard model of particle physics, describing how just three fundamental forces glue together three fundamental particles to create the world around us. But the theory does not tell us why the particles have the masses they have, why the forces have…

Alan Chodos, James Riordon MIT Press £25 • HB Ghost Particle tells the story of the prediction, discovery and observation of one of the Universe's most elusive particles: the neutrino. This is really a book about particle physics and seems to be aimed at someone who already has a grasp of basic physics. There are relatively simple explanations of some concepts and analogies abound, but the subject is so complex and (at times) subtle, that some basic familiarity is likely to be essential to avoid getting lost. After an introductory overview, the book starts by covering the history of the neutrino. Somewhat oddly, the history is not purely chronological, but there's an organisation by ‘topic’. While this perhaps simplifies having to flit between complex topics, it does mean keeping track…

1 Monocular telescope building kit Price £30 • Supplier Royal Museums Greenwich • https://shop.rmg.co.uk Build your own refracting telescope and tripod from 314 laser-cut pieces that slot together without the need for glue. The end result is a functional telescope that's also a great showpiece and educational tool. 2 Constellation notebook Price £13.95 • Supplier Joanie Home • www.joaniehome.com Combine convenience with style. The soft cover is patterned with gold foil stars and has a loop to hold the supplied gold pen. The 160 ruled pages are solidly bound to keep all your notes securely together. 3 Antlia 1.25-inch H-beta and OIII filter Price £99 • Supplier First Light Optics • www.firstlightoptics.com Specifically designed for visual observing nebulae, this filter lets through 90 per cent of the light from OIII…

Television Find out what The Sky at Night team have been exploring in recent and past episodes on page 18 Online Visit our website for competitions, astrophoto galleries, observing guides and more Social media Follow us on Twitter, Facebook and Instagram for space news, astro images and website updates Podcasts Listen to our Radio Astronomy podcasts where the magazine team and guests discuss astro news Tablet/phone Get each month's issue on your Apple or Android device, now with bonus image galleries eNewsletter The best targets to observe each week, delivered to your inbox. Visit bit.ly/skynewsletter Find out more at: www.skyatnightmagazine.com…

It's been obvious for a while now that our best theories of cosmology have a problem. Though we can build computer simulations that do a good job of reproducing the cosmos we see around us, they rely on the presence of dark matter. This mysterious dark matter, which outweighs normal, visible matter by a factor of six to one, is needed to provide the gravitational heft to form the structure of galaxies and galaxy clusters but must not interact with light. We need something that is massive, and which is dark. It's only natural to think that black holes might be part of the answer. We know from surveys looking for the effect of passing black holes on background stars that there are not anywhere near enough large black holes…

Searching for Alien Life The launch this April of the JUICE mission to Jupiter and its icy moons marks a new era in the search for habitable conditions beyond our planet. The Sky at Night meets scientists who are collecting samples from Mars, exploring the Jovian system and beyond to find out how we're looking for extraterrestrial life - and whether we'll know when we've found it. Four, 10 April, 10pm (first repeat will be on Four, 13 April, 7pm) Check www.bbc.co.uk/skyatnight for more up-to-date information…

The Future of Geography Sheffield Central Library, Sheffield, 24 April, 6:30pm Author and journalist Tim Marshall gives a talk on the politics of space and how humans are taking their power struggles with them as they explore the Solar System. Free. www.eventbrite.co.uk/o/libraries-sheffield-9795467632 Astronomy history conference Lyttelton Lecture Theatre, Birmingham, 1 April The Society for the History of Astronomy hosts a day of fascinating talks, headlined by Carolyn Kennett on the 1820s Dolcoath Mine experiments to calculate Earth's gravity. £20 for non-members. societyforthehistoryofastronomy.com/meetings Astronaut Academy Observatory Science Centre, Herstmonceux, East Sussex, 4 April Half-day workshops for children aged 6-8 and 9-11, discovering what it takes to become an astronaut, doing robot arm experiments and learning about life in microgravity. £14.95 per child. www.the-observatory.org/events/astronaut-academy The Hidden Universe 14 April, 8pm Dr Jeni…

16-PAGE CENTRE PULLOUT MERCURY RISING Follow the elusive world as it climbs in the evening sky OUT LIKE A LIGHT Watch the star Alniyat vanish behind the Moon About the writers Astronomy expert Pete Lawrence skilled astro imager and a presenter on The Sky at Night monthy on BBC Four Steve Tonkin is a binocular observer. Find his tour of the best sights for both eyes on page 54 Also on view this month… Spy the Moon's Spitzbergen mountains ✦A favourable peak for the Lyrids ✦ Venus and the Moon in the daylight sky Red light friendly To preserve your night vision, this Sky Guide can be read using a red light under dark skies Get the Sky Guide weekly For weekly updates on what to look out for in…

Universal Time (UT) and British Summer Time (BST) Universal Time (UT) is the standard time used by astronomers around the world. British Summer Time (BST) is one hour ahead of UT RA (Right ascension) and dec. (declination) These coordinates are the night sky's equivalent of longitude and latitude, describing where an object is on the celestial ‘globe’ Family friendly Objects marked with this icon are perfect for showing to children Naked eye Allow 20 minutes for your eyes to become dark adapted Photo opp Use a CCD, planetary camera or standard DSLR Binoculars 10×50 recommended Small/ medium scope Reflector/SCT under 6 inches, refractor under 4 inches Large scope Reflector/SCT over 6 inches, refractor over 4 inches GETTING STARTED IN ASTRONOMY If you're new to astronomy, you'll find two essential reads…

On the morning of 10 April, a bright 83%-lit waning gibbous Moon occults mag. +2.9 Alniyat (Sigma (σ) Scorpii). The event starts around 03:33 BST (02:33 UT) when the Moon sits 11° above the southern horizon as seen from central UK, the Moon's southwest limb hiding the star. Reappearance occurs when the Moon is due south, Alniyat reappearing from the Moon's dark southeast limb at 04:30 BST (03:30 UT). Times are given for the centre of the UK and may vary by a few minutes depending on location. Observing lunar occultations of bright stars is rewarding. Watching the star through an eyepiece before disappearance helps you appreciate how fast the Moon's apparent motion is in the sky. A lunar occultation of a star happens quickly. Lose concentration or blink at…

KEY TO STAR CHARTS When to use this chart 1 April at 01:00 BST 15 April at 00:00 BST 30 April at 23:00 BST On other dates, stars will be in slightly different positions because of Earth's orbital motion. Stars that cross the sky will set in the west four minutes earlier each night. How to use this chart 1. Hold the chart so the direction you're facing is at the bottom. 2. The lower half of the chart shows the sky ahead of you. 3. The centre of the chart is the point directly over your head. Sunrise/sunset in April* Moonrise in April* Lunar phases in April MORE ONLINE Paul and Pete's night-sky highlights Southern Hemisphere sky guide…

1 M44 Our first target needs no introduction, M44, the Beehive Cluster, sits at the heart of Cancer, boxed in by Asellus Borealis (Gamma (γ) Cancri), Asellus Australis (Delta (δ) Cancri), Eta (η) and Theta (θ) Cancri. The cluster is rich, large and visible to the naked eye under dark skies. With an estimated distance of 594 lightyears, it's one of the nearest open clusters, appearing 95 arcminutes across. It contains over 200 members, 20 brighter than mag. +8. M44 contains many multiple stars and in excess of 100 variables. Most appear towards the yellow-red end of the spectrum, but one stand-out variable star, TX Cancri (mag. +7 to +8) appears blue. □ SEEN IT 2 NGC 2672 Next is the elliptical galaxy NGC 2672. Wander to the southernmost edge…

If you're new to stargazing, a faint object like C/2022 E3 ZTF, the comet that had us all excited earlier this year, isn't the best target for a first look through a telescope – the chances are you won't see a thing. The eye is a remarkable detector, but to see faint objects like this it helps to understand both its limitations and the tricks you can use to coax the maximum out of its short-exposure capability (unlike a DSLR camera, long exposures aren't an option with the eye). Of course there are other limiting factors. Light pollution, impatience, a poor night for seeing, and not spending long enough dark-adapting your eyes can all play a part, as can using the wrong magnification and not keeping your telescope's optics clean…

Whether you're a seasoned astrophotographer or a beginner just starting out, we'd love to see your images. Send them to us at www.skyatnightmagazine.com/send-us-your-astrophotos We've teamed up with Modern Astronomy to offer the winner of next month's Gallery a Hama lens pen, designed for quick and easy cleaning of telescope optics, eyepieces and camera lenses. It features a retractable brush and non-liquid cleaning element. www.modernastronomy.com • 020 8763 9953…

KEY SCIENCE The One Thing You Need To Know Marcus Chown Michael O'Mara £16.99 • HB Did you know that your stomach generates heat at a greater rate than a chunk of the Sun of the same size? Or that the brain is 10,000 times more energy-efficient than a supercomputer? I know I didn't! The One Thing You Need To Know by Marcus Chown is a book for those curious about scientific concepts, but who were perhaps put off by the mind-boggling details of typical science books. Because to understand gravitational waves you first need to understand Einsteinian gravity in excruciating detail and be an expert in tensor calculus, right? Wrong! Chown takes 21 concepts and cleverly starts with just one thing that you need to know to understand that…

Tim Hunter University of Arizona Press £25.95 • PB Sometimes it seems there are as many guides to stargazing as there are stars in the sky. The Sky at Night (which has no connection to this magazine or the BBC series) takes us through the basics of amateur astronomy before dedicating chapters to the Moon, planets and stars, and advice on buying equipment. The book's unique selling point is its author is one of the founders of the International Dark Sky Association (IDA), as well as a dedicated amateur astronomer. The informal and friendly tone is ideal for novices who may feel intimidated when faced with the vast night sky, and the diagrams are clear and nicely drawn. But given the emphasis is mostly on naked-eye observations, it would have…

Thomas Hertog Torva £20 • HB Any work staking a claim to the legacy of A Brief History of Time has big shoes to fill. Nevertheless this new book by Hawking's former doctoral student and collaborator Thomas Hertog comes complete with the bold subtitle ‘Stephen Hawking's final theory’. And, fortunately, On the Origin of Time is more than up to the task. Hertog sets out to tell the tale of a quest that has formed the bedrock of his own career and the final two decades of Hawking's: the search for an explanation of just how our remarkably life-friendly Universe came to arise from among the infinite possibilities embedded in the Big Bang. The result is a new theory of ‘quantum cosmology’ in which longstanding incompatibilities between gravity (described by…

Will Gater Astronomy expert “It'll be a while before JUICE arrives at Jupiter, but I genuinely can't wait to see what the mission has to tell us about the incredible icy worlds that orbit the giant of our Solar System”. Read more about JUICE, page 28 Charlotte Daniels Practical astonomer “Oftoverlooked, Mercury will be a great target to observe in the evening twilight in April. I'm looking forward to exploring the inner planet this month.” Charlotte reveals how to make the most of Mercury, page 34 Shaoni Bhattacharya Science journalist “The number of satellites going into space in the near future is staggering, and this was a topic of great discussion at the Abu Dhabi Space Debate.” Hear more about the international debate, page 60…

Email us at inbox@skyatnightmagazine.com MESSAGE OFTHE MONTH This month's top prize: two Philip's titles The ‘Message of the Month’ writer will receive a bundle of two top titles courtesy of astronomy publisher Philip's: Nigel Henbest's Stargazing 2023 and Robin Scagell's Guide to the Northern Constellations Winner's details will be passed on to Octopus Publishing to fulfil the prize Drawn to comets Comet C/2022 E3 ZTF has been a delight, watching it rise in the morning and evening sky. A comfy seat and some simple sketches gave a view of this memorable sight, clearly seen from town. There was hardly any difference in the views from my 6-inch achromat or 15×70 binoculars. The coma looked green and a wide tail was seen by averted vision and noting which area of the…

8 Saturday As the Moon moves out of the way, this is a good time to try for our Deep-Sky Tour targets, which this month are located Cancer (see page 56). 9 Sunday As the sky darkens this evening, mag. -3.9 Venus is south of the Pleiades open cluster. Closest approach is tomorrow evening when they appear 2.7° apart. 11 Tuesday Mercury reaches greatest eastern elongation, when it's visible 19.5° from the Sun in the evening sky after sunset. 13 Thursday Venus is positioned between the Pleiades and Hyades open clusters today. 14 Friday Mag. +1.2 Mars sits 9.5 arcminutes from mag. +3.0 Mebsuta (Epsilon (ε) Gemininorum) this evening. 15 Saturday A good day to align sundials, as the difference between the apparent and mean Sun align today (equation of time = zero). The Sun is…

Over the last few years there has been an explosion of multi-band filters for astrophotographers. Used with a colour astro camera, they help to combat light pollution and make it easier to image deep-sky targets from cities. Compared to mono cameras, one-shot colour cameras also help in this regard as they save time imaging. Combining data captured with a multi-band filter and with a standard light-pollution filter allows some good creativity when it comes to processing; the colour can be changed, and stars moved from one image to another to give some very impressive results. Here we have examined a selection of multi-band filters to look at the differences in the wavelength of light they let pass through to the camera sensor. There are dual-band filters, which mainly pass the…

Telescope Check your telescope is in good working order, with clean optics. If it's a reflector, make sure that its mirrorrs are accurately collimated. Eyepieces High-quality eyepieces will maximise your chances of seeing faint objects. A rubber eyeguard will exclude stray light. Weather check The best crystal-clear nights often come when a cold front or a northerly air stream moves down the country. Check the Met Office's weather maps for the latest forecast. Dark site Darker skies are better, of course, but if yours aren't you can block out streetlights by carefully positioning your scope or using fence panels as shields.…

The world of astrophotography can be daunting, and learning image processing can be a particularly steep learning curve. Any help that can boost our editing skills is a bonus. In Adobe Photoshop, ‘actions’ can help to overhaul your processing workflows. These are a set of steps that can be saved and replayed on future images to, for example, boost contrast or reduce noise. You can also purchase actions created by someone else. One such set is Annie's Astro Actions, a comprehensive set of 24 different workflows that can guide you through the editing process, from simple step-by-step guides, and combining mono images into RGB or the Hubble Palette, to stretching and star removal. A full list of actions is available to view at www.eprisephoto.com/astro-actions prior to purchase. Once purchased, download…

When to use this chart 1 April at 00:00 AEDT (13:00 UT) 15 April at 23:00 AEST (13:00 UT) 30 April at 22:00 AEST (12:00 UT) The chart accurately matches the sky on the dates and times shown for Sydney, Australia. The sky is different at other times as the stars crossing it set four minutes earlier each night. APRIL HIGHLIGHTS A rare hybrid solar eclipse occurs on 20 April. Starting out as an annular eclipse in the southern Indian Ocean, it then changes into a total before reaching the westernmost tip of Australia. The centre line will experience 60 seconds of totality at 11:30 WST. All states will see partial phases with maximum eclipse occurring in Perth at 11:21 obscured by 71%, Adelaide (13:30, 21%), Darwin (13:52, 81%), Melbourne…