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Telescope House April Sky Guide

April is here and we in the northern hemisphere are now beyond the Vernal Equinox, meaning the Sun is now a resident of the northern celestial hemisphere.  With this comes extra hours of daylight and decreasing hours of darkness.  In this sense, April brings a mix of blessings and challenges. While it heralds the arrival of more favourable weather, particularly in milder regions, those of us residing in higher northern latitudes must confront the diminishing hours of darkness, particularly towards the month's end. Despite the common notion of "April Showers," statistical evidence, especially in Europe, suggests this may be more of a myth. In fact, April tends to be relatively dry compared to the preceding months. Nonetheless, as we eagerly anticipate improved weather conditions - no matter where you find yourself, there’s plenty to see in the skies above us this month.



The Solar System



The Sun


The Sun’s activity is still increasing, with a number of very recent outbursts, resulting in Aurora being visible from lower than usual latitudes.  The every large AR3615 sunspot group appears to have been the source of the most recent - at time of writing - and threatens yet more activity.  Quite when Solar Maximum will occur is still difficult to pin down.  We will definitely know when it is past, but predicting the true peak is trickier.  Websites such as www.spaceweather.com and Michel Deconinck’s monthly newsletter: https://astro.aquarellia.com/doc/Aquarellia-Observatory-forecasts.pdf cover many aspects of solar observations and are well worth checking out.


The Sun comes dramatically into focus this month with April 8th’s total solar eclipse, which will be visible across a wide track of the United States of America and Mexico and eastern Canada. The eclipse will be seen outside the track of totality across a very wide area, stretching from Hawaii out into the middle of the Pacific to the West Coast of Ireland. The track of the eclipse will also skirt the very top of South America, right the way up to Alaska, though at the border of its visibility in these areas, will be extremely partial.  Iceland, Scotland, Ireland, and the extreme north of Spain and Portugal Macy, the very partial phases of the eclipse at Sunset. Wherever you plan to watch this event from, as ever, we urge caution and sensible use of solar filters, solar telescopes and eclipse classes, unless the eclipse is completely total and fully eclipsed from your observing site. We wish everyone travelling to see the full track of the eclipse, the very best of fortune with the weather.



The Moon


The Moon will begin April at a 60% illuminated waning gibbous phase. A resident of Sagittarius. The Moon will not rise till sometime past 3 am on the 1st, and will transit at a little before sunrise at just after 6:30 am. Being so low in the sky, in the most southern part of the ecliptic, means that lunar observations will be understandably truncated somewhat by less than ideal elevation during this period.  The Moon will reach last quarter phase on 3rd April and will spend the next week approaching the Sun and rapidly decreasing its phase as it does.


On the morning of 6th April, the Moon will draw alongside Saturn and Mars in Aquarius where its thin crescent will pass to the south of both planets as the Sun rises. The following morning, the Moon will come into close proximity with the brighter Venus making this the easier of the two conjunctions to witness.


New Moon will occur on April 8th, which, as previously mentioned, will coincide with a total solar eclipse visible from Mexico and a wide track of the continental United States and on into eastern Canada. 


After the excitement of the eclipse is over, the Moon will become an evening object. Rising up at quite steep angle, our natural satellite will pass through Pisces, Aries (where it will meet Jupiter on the evening of April 10th) and on into Taurus and Gemini, where it will reach first quarter phase on April 15th. This month’s evening apparition of the Moon is one of the aforementioned “High Spring Crescents” (for observers in higher northern latitudes), and represents a fantastic opportunity to view the Eastern limb of the Moon at high surface relief. Those with telescopes are thoroughly encouraged to make the most of lunar observation at this time.


Post first quarter, the Moon continues its journey down through Cancer and on into Leo and then into Virgo where it becomes full on April 23rd. As usual, we point out that this part of the month will not be the most agreeable for deep sky observation or imaging.


After reaching full, the Moon will cross over the border from Virgo into Libra, and then on into Scorpius and Ophiuchus, before returning to Sagittarius on the 30th, where we first picked it up at the beginning of the month. By this point, the Moon will be around 66% illuminated waning gibbous phase.


Mercury 


We begin April with Mercury as an evening object, in a favourable separation from the Sun, at around 15°, but rather faint at +1.7 magnitude. The reason for this is that the planet is drawing around the Sun towards us and is rapidly decreasing its phase as it does. At the beginning of April, Mercury will show a crescent phase eliminated by just under 15%. As the first week of April continues, mercury gets fainter and fainter, making it extremely difficult to pick out in the glare of the evening sky.  The evening of the 7th finds Mercury at just 2.8% illumination and a visual magnitude of +3.9. By this point, readers will get no prizes for guessing, the planet will be completely unobservable.


Mercury reaches inferior conjunction, in-between the Sun and the Earth as viewed from our perspective, on April 12th. Beyond this point, it will become a morning target. However, the ecliptic plane, which Mercury runs along, rises at a very shallow angle from the horizon in the mornings at this time of year (from the northern hemisphere). As such, although Mercury will rapidly move away from the Sun, it will still remain a challenging target, even at the end of April. On the morning of the 30th, Mercury will stand around 4 1/4° high in the east (as viewed from 51° north), as the Sun rises. This, coupled with a magnitude of around +1.2 will make it a tricky target to find, unless atmospheric conditions are extremely kind.  

Venus 


The planet Venus displays an impressive visual magnitude of -3.9 at April’s beginning. A resident of the Pisces Aquarius borders, the planet sits around 17° from the Sun at the beginning. However, as previously mentioned, in regards to Mercury, Venus is sitting in a very low lying part of the ecliptic as viewed in the morning sky. As such, the planet will only attain an altitude of around 2 1/2° high as the Sun rises (as observed from 51° north). It is perfectly possible to see Venus during daylight hours, the fact the planet is sitting so low to the horizon at sunrise does not count in its observing favour.


Venus is still headed sunward - and by the time we reach the middle of April has decreased its separation from the Sun to just over 13°. This has done Venus no favours whatsoever and the plan is considerably more challenging to observe, attaining a height of under 2° elevation as the sunrises on the morning of the 15th.


Fast forwarding to the end of April, Venus has decreased its separation from the Sun to around 9 1/2° and will now sit a little over one 1/4° high above the horizon (as observed from 51° north), as the Sun rises.  Remarkably, Venus is still some weeks from superior conjunction, which will reach in early June. Those in the equatorial regions of the Earth will fair distinctly better as far as observing Venus is concerned, but those of us in mid northern latitudes will be advised to look elsewhere for observing highlights.


Mars


The Red Planet starts April as a resident of Aquarius and most definitely a morning target. The planet, at the month’s beginning, is separated from the Sun by just under 35° and will attain an elevation above the horizon of about 7 and 1/4 degrees (as observed from 51° north), as the Sun rises on the 1st. At a visual magnitude of +1.2, Mars will still be a tricky target to pick out in the dawn sky at this point.


The trend as far as Mars is concerned, is upwards, albeit slowly. By the end of April, Mars will be sitting in Pisces at a visual magnitude of +1.1, and an elevation of just under 10 degrees (as observed from 51° north). By this point, Mars will have separated itself from the Sun by just under 41°. It will still be a relatively tricky target to pick out in the glare of the morning sky, and is still somewhere off its best, which it will reach at the end of this year and beginning of the next.


Jupiter


The King of the Planets is still in a reasonably favourable position for observation in the early evening in early April. The evening of the 1st sees Jupiter standing around 29° high in the sky (as observed from 51° north) and shining at a steadily brilliant visual magnitude of -2.1.  The planet at this time presents a disc of around 34 seconds diameter and will set at around 3 1/4 hours after the Sun.


However, as alluded to in last month’s sky guide, the window for meaningful observation of Jupiter for this season is rapidly closing. The planet is headed sunward - and by mid-April will stand at around 19 1/2° above the horizon at sunset. By the time we get to the end of the month, this is decreased yet further to just under 9 1/2°. As such, it is obvious that those interested in observing Jupiter really must skew observations to the early part of the month to make the most of the opportunity this gives us. Jupiter will reach superior conjunction in mid May, and will then emerge as a morning target.  


There were a few mutual transit events as far as Jupiter is concerned that are worth observing during April. The evening of the 1st, sees a mutual Great Red Spot and Io/Io shadow transit, which begins at round 8:40 pm (BST).  There is a nice Io and Io shadow transit, which occurs as a little before 8 pm on April 17th.   There’s also a favourable Ganymede and GRS transit which occurs just before sunset on April 30th. 


Saturn 


Saturn, like Mars and Venus is a morning target at the beginning of April, and just like it neighbours is sitting in a very shallow rising part of the ecliptic at present. At +1.1 magnitude and apparent size of 15.7 seconds diameter on the morning of the first, Saturn will be difficult to pick up without optical assistance in the glare of the morning sky. The planet will stand at an altitude of around 5° elevation as the sunrise is on the 1st, which will make it doubly challenging to observe. The brighter Venus, sitting around 11 1/2° to the west, will serve as a useful marker for finding the Ringed Planet.  However, as previously mentioned, the elevation of all the planets in the morning sky at present, is pretty pitiful from higher northern latitudes and precludes meaningful telescopic observation at any significant magnification.


By the time we reach the end of the month, Saturn has faded a little to +1.2 magnitude, but has increased its angular size to just over 16 seconds. The reason for this decrease in magnitude, while the planet has increased its angular size, is largely down to the separation of its rings, which are closing at present and thus decreasing the planet’s overall brightness. While we challenge most, if not all, observers to tell the difference between 0.1 of a magnitude’s difference in relatively bright object, it is certainly interesting to consider the part that Saturn’s rings play in its overall brightness. The narrower Saturn rings get from our perspective here on Earth, the less light that they reflect back to us. The mean difference in brightness of Saturn when its rings are wide open, to when they are completely closed is around half a magnitude. We will cross Saturn’s ring plane from our perspective on earth on 23rd March 2025.


Uranus and Neptune


Of the two outer gas giants, Uranus is by far and away the best observing target during April. Uranus’ proximity to Jupiter during April, makes it relatively easy to find in the constellation of Aries in the evenings. Towards the end of the month, on the evenings of the 20th and 21st, Uranus and Jupiter can be found around half a degree from each other in the sky. this means the both planets will fit into a low-power telescopic view, making ready identification of Uranus even easier.


Neptune, on the other hand, is located between Venus and the Sun in early April, but will be impossible to find in the glare of the dawn. The latter part of the month sees Neptune and Mars exceptionally closely placed to each other. On the morning of the 30th, the two will be found just over three arc minutes from each other in the sky. Unfortunately, while it may be possible to locate Mars in exceptional circumstances, it will be impossible to view Neptune with the sky being so light and both planets being so low in the sky. 



Comets


12P/Pons-Brooks is the only comet of reasonable brightness easily observable during the first part of April. It should start the month around 5th magnitude and will be observable in the evening sky. The comet is a resident of Aries in early to mid month and will set at a little before 11 pm and rises at just after 6.30 am the following morning on the 1st/2nd April.  As the month begins the comet into be found close to Alpha Arietis, Hamal - the principal star in Aries.  12/P will drift towards Jupiter towards the end of the first week of the month, making its location easier to find.  Although 5th magnitude is technically naked eye, the comet’s brightness will be spread out over a wide area, so will definitely need binoculars and/or a telescope to observe it. As the month progresses, the comet brightens, but sinks further towards the Sun, making it increasingly difficult to observe.  The Moon will also start to potentially affect observing beyond the 10th.  As long as the weather improves, there is a good chance of observing the comet at close to its best.


13P/Olbers will be making its way through Taurus during April. This will be considerably less prominent than 12P at around 10th magnitude (though some estimations of brightness at time of writing are already higher than this).  The comet should be relatively straightforward to find in larger binoculars and small telescopes. 13P will continue to brighten after the end of the month and should reach 7th magnitude - possibly brighter - in May, June and July.

C/2023 A3 (Tsuchinshan-ATLAS) is still showing very reasonable progress. The comet is 12th magnitude at time of writing, but it now predicted to reach around a minimum magnitude of +0.0 - and could become even more spectacular - when it reaches its peak in September to November of this year. While much remains uncertain in the interim period between now and then, we maintain a cautious, yet hopeful outlook for a good showing from this comet.




Meteors



Peaking on the night of the 21st-22rd April, the Lyrids are a regular, reliable shower.  While rarely as spectacular as the major showers such as the Perseids and Geminids, they are nonetheless worthwhile looking out for.  Unfortunately, this year, the Moon - the ever-present nemesis of meteor showers - is very close to full around the peak of the shower and will spoil the potential 


The Lyrid meteor shower originates from its parent comet, C/1861 G1 (Thatcher), which is a medium-period comet set to return around 2276. When these comet remnants collide with the Earth's atmosphere, they do so at a relatively gentle pace of 48 kilometers per second. Consequently, the resulting meteors tend to have modest kinetic energy. Additionally, due to their small grain sizes, Lyrid meteors generally aren't exceptionally bright, averaging around +2.0 magnitude. However, approximately every 30 to 60 years, Earth encounters a denser portion of Comet Thatcher's debris field, leading to zenith hourly rates that can reach several hundred. In typical years, the Lyrid meteor shower peaks at a zenith hourly rate of around 20, although not all may be visible. Despite the lunar interference, with clear skies in your area, you could still capture the brightest Lyrids with short-exposure DSLRs or USB imagers equipped with All Sky Lenses.


Click here for part 2 of the April Sky Guide

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