The night sky in April 2021

posted 29 Mar 2021, 02:07 by Pete Collins   [ updated 29 Mar 2021, 11:55 ]
by Anne Holt

Sunrise     1st:   06.42       30th:   05.36

Sunset      1st:   19.44       30th:   20.37


Astronomical Darkness

1st:      21.50 to 04.33       30th:    23.23 to 02.48


Day Length  1st:  13:02:32  30th:  15:01:07


New Moon:  12th at 03.33

Full Moon:    27th at 04.33 (angular diameter 33' 23")


Lunar apogee:   14th at 18.48  (406119 Km, angular diameter 29' 41")

Lunar perigee:   27th at 16.25  (357378 Km, angular diameter 33' 25")


Because this month's full Moon is only 12 hours before perigee, the second closest of this year, it will appear slightly larger and brighter than average - a Supermoon.  It is also known as a perigee-syzygy Moon, a syzygy being 3 or more astronomical objects (in this case the Sun, Earth and Moon) in a straight line.


The most common name for the April full Moon is the Old Farmer's Almanac’s Pink Moon.  It's no more likely to appear pink than last month's was to resemble a worm, the name comes from the colour of phlox flowers, one of the first blossoms to appear in Spring.

Other names include the Colonial American Planters Moon, the Celtic Growing Moon or Hare Moon, the Medieval English Seed Moon, the Neo Pagan Awakening Moon and the Old English/Anglo Saxon Egg Moon. For the Chinese it was the Peony Moon and, as always, Indigenous Americans had their own, descriptive, names.  It was the Cherokee Flower Moon, the Choctaw called it the Wildcat Moon and it was the Ojibwa tribe's Sap Running Moon.  The Dakota Sioux were a little more precise - The Moon when Geese Return in Scattered Formation.  They seem to be a little behind some other tribes, whose geese returned last month.


Highlights


Again, rather more lows than highs.  Jupiter is low in the dawn sky for much of April, but might be visible in the morning twilight towards month end.  The fainter Saturn is more difficult to see despite being slightly higher.  Mercury, Venus and Uranus all appear close to the Sun for most of the month, but might be spotted in the evening sky - Uranus at the start of April, the other two right at the end of the month.  Only Mars is high enough to be seen easily, but is getting lower in the evening sky as the month progresses.

We have one comet, high in the sky, not expected to reach naked eye visibility, starting the month around mag 6.8, fading to 8.3 by late April.

At last we have a reasonably active meteor shower, the Lyrids, but the bad news is that the gibbous Moon is above the horizon for most of the peak night.

And the nights are getting shorter (and starting later, thanks to BST), on 1st we have 6hrs 47 minutes of astro darkness, about half that by the end of April.


There are also a couple of events with astronomical connections.

On 12th, it will be 60 years since Yuri Gagarin became the first human to go into space, albeit for just one orbit lasting 108 minutes. His Soyuz capsule reached 327 km above Earth - by accident.  It was intended to orbit at 230 km but an engine failing to cut out took it much higher.  He came down 300km from the intended landing site, his parachute landing was watched by a farmer and her daughter.  He told them that he was a Soviet citizen who had descended from space and must find a telephone to call Moscow.

The site is now a memorial park, Gagarin Field, with a 25 metre stylised rocket shaped monument and a statue of the first cosmonaut.

And, at the start of the month we have Easter.  There is a tenuous astronomical connection in that Easter Day is the Sunday after the first full Moon on or after the Vernal Equinox.  In reality it's a bit more complicated, the date of the equinox is always taken as March 21st, even when it occurs on a different day, and the Eccelsiastical Full Moon date is used, rather than the actual one.  This is calculated using the Metonic Cycle, a 19 year period, divided into 235 months of 29 or 30 days. The first day of each month is the Ecclesiastical New Moon, the Full Moon is 14 days later.

The earliest date for Easter Sunday is March 22nd.  This happens when there is a full Moon on Saturday March 21st.  It is very rare - the last time was in 1818, it won't happen again until 2285

The latest possible date, April 25th, occurs when there is a full Moon on March 20th, the day before the equinox, and the next one is on Sunday April 18th, making Easter Day a week later.  This is a bit more frequent, the last time was in 1943, the next in 2038. 


Constellations

Now that BST has been forced upon us, we have to wait even longer for the skies to darken each evening. By the time it gets really dark the winter constellations, including the beautiful area around the Winter Hexagon, so rich in bright stars, is sinking slowly in the West.

Ursa Major is now high in the sky with the Plough overhead around midnight in the second half of the month. Follow the curve of the handle down to the orange coloured Arcturus, brightest star in the constellation Bootes the herdsman, and the 4th brightest in the night sky.
The signature constellation of spring, Leo, is still riding high in the south and the Summer Triangle of Vega (in Lyra), Deneb (Cygnus) and Altair (Aquila) is now rising in the east and visible in the early hours.

Planets


Mercury:  in Aquarius, mag -0.4

Not easily seen this month.  On 1st it is 4 degrees below the horizon at dawn. It moves into Pisces on 3rd, Cetus on 8th and back into Pisces on 11th.  It closes in on the Sun quite rapidly over the next week, reaching superior solar conjunction on 19th, when it passes 34' to the south at 02.36.  It moves into Aries the following day and on 25th is only 1 degree 12' NNW of Venus, very low in the evening sky, both set only 40 minutes after the Sun.

If you do attempt to see the pair through binoculars make sure that the Sun has completely set before trying to spot them.

On 27th Mercury reaches perihelion, 0.31AU, and by 30th, now at mag -1.2, is 5 degrees above the horizon at dusk, setting at 21.49, about 75 minutes after the Sun.


Venus:  in Pisces, mag -3.9

Appears too close to the Sun to be seen during most of April, following superior solar conjunction in late March. On 1st it sets 15 minutes after the Sun and is separated from it by just one degree. On 15th, when it moves into Aries, the separation has increased to 5 degrees. On 30th it is 3 degrees 30' in the WNW 20 minutes after sunset, but down to 1 degree by the time the sky darkens, setting at 21.21.


Mars:  in Taurus, mag 1.3

Still the only major planet which is high in the sky, though only in the early part of the night.  On 1st it will be at 43 degrees in the west, as the sky darkens around 20.30, visible until a little after midnight and setting at 02.02.  On 17th the waxing crescent Moon passes 7’ to the south at 13.08.  Observers in parts of India and SE Asia will be able to see an occultation. From the Manchester area they will be visible in the dusk sky from 21.15, with Mars 36 degrees above the western horizon, the Moon almost 4 degrees to the east. Mars moves into Gemini on 25th, when it is 32 degrees in the west as the sky fades, setting at 01.40.  On 30th, down to mag 1.5, it is at 29 degrees in the darkening sky at 21.40 and should be high enough to be easily visible until nearly midnight, setting at 01.30.


Jupiter: in Capricorn, mag -2.1

Bright but very low in the morning sky. On 1st it rises at 05.31 and reaches 5 degrees by dawn.  On 7th the waning crescent Moon passes 4 degrees 23’  to the south at 08.18.  On this day Jupiter rises at 05.10 and gets to 6 degrees by dawn.  When the Moon rises at around 05.30 the separation is 5 degrees.  By 18th the gas giant reaches 8 degrees in the SE by 05.40 as the sky brightens.  It is in Aquarius from 26th, when it rises at 04.01 and gets to 9 degrees by dawn. By the 30th it should be more easily visible to observers with a clear ESE horizon, it rises at 03.44 and is at 10 degrees soon after 5am, as dawn breaks. 


Saturn: in Capricorn, mag 0.8

Slightly higher than Jupiter in the morning sky but not so easy to spot as it is much fainter.  On 1st it rises at 05.06 and only reaches 5 degrees by dawn.  On the morning of 6th the rising 31% Moon passes 5 degrees 30’ to the south at 05.00, closest, 3 degrees 57’, in daylight at 09.30. Jupiter is 12 degrees to the east of the pair. On 30th Saturn rises at 03.13 and gets to 9 degrees before the sky gets too bright for it to be seen.


Uranus: in Aries, mag 5.9

On 1st it is only 8 degrees above the horizon at dusk, setting at 22.20. It moves closer to the Sun, by 15th they appear separated by 14 degrees, with Uranus setting at 21.28.  It is at solar conjunction on 30th, when it is 24’ to the south at 2055, about 20 minutes after the planet has set.


Neptune:  in Aquarius, mag 8.0

Very low in the morning sky following March’s conjunction. On 1st it rises at 06.20 but appears only 20 degrees from the Sun - much too close for safe binocular or telescope observing.  On 30th it is still 5 degrees below the horizon as the sky begins to brighten, rising at 04.29.


Dwarf Planets


Ceres: in Cetus, mag 9

Too close to the Sun to be seen in April. On 1st they appear separated by only 8 degrees.  It is at solar conjunction on 7th, when it passes 6 degrees 30’ to the south.  When it moves into Pisces on 22nd, the separation is 10 degrees. On 28th it is in conjunction with Eris, passing it 4 degrees 54’ to the south. Ceres is still only 13 degrees from the Sun, so the conjunction wouldn’t be visible - even if you could see the much more distant, almost 10,000 times fainter Eris.  On 30th Ceres rises at 06.01 still  only 14 degrees from the Sun.


Pluto:  in Sagittarius, mag 15.1

Much too low for imaging or telescopic observation, as it will be for many years yet - at least for anyone in the northern hemisphere. 

As you probably know, it’s highly elliptical orbit crosses that of Neptune, so it spends almost exactly 20 years of each 165.4 year period closer to the Sun than the ice giant, the last time being from Feb 7th 1979 to Feb 11th 1999.  

However, because the 2 bodies are in resonance - Pluto makes 2 journeys round the Sun in the same time that Neptune does 3 - they will never collide, never even come close. Pluto actually gets much closer to Uranus (11AU) than it does to Neptune (14AU).


The other two Kuiper Belt Dwarf Planets are high in the sky, but so faint that they are only targets for the most experienced astrophotographers.


Haumea:  in Bootes, mag 17.3

High enough for imaging for most of the night.  On 1st it is 21 degrees in the east when the sky darkens, culminating, 52 degrees in the south, at 02.57 and still 43 in the SW at dawn.  It is at opposition on 18th, when it is 30 degrees in the east as the sky gets dark, 52 degrees in the south at 01.51 and 41 degrees in the SW when the sky begins to brighten.  On 30th it is 41 degrees at dusk, 52 degrees in the south at 01.01 and 40 degrees in the SW at dawn.


Makemake:  in Coma Berenices, mag 17.1

Also high enough for imaging throughout the hours of darkness. On 1st it is 31 degrees in the east as the sky darkens, soon after 9pm, culminating at 01.46 when it reaches 59 degrees. By the time the sky gets bright at around 05.15 it is still high - 40 degrees in the west.  On 30th it is 56 degrees in the SE as darkness falls, 59 degrees south at 23.46 and 35 degrees in the west at dawn.


Eris:  in Cetus, mag 18.8

Appears very close to the Sun throughout April.  On 1st, when it sets at 20.13, the separation is 17 degrees. It is at solar conjunction on 14th, when it rises at 07.28, sets at 19.22 and appears 11 degrees south of the Sun,  The separation at conjunction is much higher than the major planets because Eris’ orbit is inclined to the ecliptic by 44 degrees. On 30th it rises at 06.25, almost an hour after sunrise, still only separated by 18 degrees.



Asteroid 9 Metis

Discovered on April 25th 1848 by Andrew Graham.  Its main claim to fame is that it was the first one found by observations made in Ireland. It contains half a percent of the total mass of the asteroid belt and was named after a Titaness, the mother of prudence and wisdom.  It shouldn’t be confused with Jupiter’s innermost moon, also named Metis, which wasn’t found and named until over 100 years later.

Metis takes 3.69 years to orbit the Sun at a distance ranging from 2.1 AU to 2.68 AU.

It begins April in Virgo, at mag 9.5, rising at 19.38, reaching 21 degrees in the east soon after 22.15 and culminating, 37 degrees in the south, at 01.45.  It remains high enough for observation for the rest of the night. It is at opposition on 5th, reasonably high throughout the hours of darkness, culminating at 10.13, when it is 37 degrees above the southern horizon. By 30th, down to mag 10.1, it is higher than 21 degrees between 22.25 and 03.00, highest point, 38 degrees, at 23.22. 



Comets


C/2021 A1 (Leonard) in Ursa Major.

Still very faint, now around mag 17.8, but high in the sky for most of the night, well positioned for anyone ambitious enough to try imaging it before it gets so bright (we hope) that everyone is having a go.

It is currently circumpolar, on 1st it is 56 degrees in the NE at dusk, highest point, 82 degrees above the northern horizon (or, if you prefer, 98 degrees in the south) at 01.23 and down to 58 degrees in the NW by dawn.  On 30th it is 81 degrees in the north when the sky gets dark, dropping to 47 degrees in the NW by daybreak.


C/2020 R4 (ATLAS)

Those of you who saw Dave Bell’s February talk on comet naming will be able to work out that this is a non periodic or long period comet, the fourth found in the second half of September 2020, by astronomers studying images taken by NASA’s robotic Asteroid Terrestrial-impact Last Alert System, which searches for possibly hazardous near Earth objects - and, along with other similar surveys, also finds lots of comets.

On 1st it is in Aquila, mag 6.8, rising at 02.28 and reaching 22 degrees in the SE by dawn. It moves into Ophiuchus on 14th, but it’s only a fleeting visit, the following day it goes into Hercules, rising at 22.42 and visible from a little before 01.30, reaching 45 degrees by dawn. It is at its closest to Earth, 0.46 AU, on 23rd and crosses into Corona Borealis on 24th, when it is at 30 degrees in the east as the sky darkens, highest point, 65 degrees, at 03.14 and not much lower in the SW at daybreak.   On 30th it is down to mag 8.3 but still high - 56 degrees in the east at 22.23, 69 degrees south at 00.36 and 52 degrees in the west at dawn. 



Meteor Showers


One reasonably active shower this month, unfortunately marred by the presence of the waxing gibbous Moon, which doesn’t set until around 5am, in nautical twilight, on the peak nights.


Lyrids:  active 14th to 30th, peak on 22nd but usually shows good activity on the nights before and after.  ZHR 18, under ideal conditions, from the darkest areas around Greater Manchester, maybe as many as 16.  The peak is at 14.00 on 22nd, so the best time to look is before dawn on that day, when the radiant is high in the sky.  For those who don’t like to get up early, even for astronomy, it might be worth trying in the early evenings of 21st and 22nd.  The shower does occasionally produce higher rates, in 1982 a ZHR of 90 was recorded, but nothing like that is predicted for this year.

It is thought that this used to be a much more prolific shower, in 687 AD Chinese astronomers reported seeing meteors falling like rain.

They are medium speed meteors which don’t usually leave trails, but the shower could include a few fireballs. Parent comet C/1861 (Thatcher).


Alpha Virginids: active March 10th to May 6th, peak April 7th (or maybe not - one source says 18th), ZHR 5-10. The radiant is close to Spica, very low from our latitude so likely numbers much lower. They are very slow moving, parent body is asteroid 1998 SH2.

This shower isn’t mentioned in this year’s IMO calendar, which indicates that studies of the associated dust cloud show that Earth won’t pass through it this time round.  


Pi Puppids: the radiant of this is so low that we won’t see any activity from the northern hemisphere.  For anyone south of the equator, the shower is active from 15th to 28th, peak on 23rd, ZHR variable. They are very slow moving meteors, parent comet 26P/Grigg-Skjellerup.


There may be some daytime activity from the April Piscids on 22nd, around 17.00.  Detectable only using radio or radar equipment.

This shower isn’t recognised by the IAU.


The ANT is active in April, the radiant is in SE Virgo at the start of the month, moving eastwards into LIbra.


Credits

Most of the solar system information given here is from:
More information, exact co-ordinates and finder charts of all solar system objects can be found on this site.

Also quite useful is https://theskylive.com

Other information is from various internet sources, including NASA, Britannica, Space Facts, Universe Today and, when all else fails,Wikipedia.















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