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Telescope House February Sky Guide

The Solar System

 

The Moon

 

The Moon starts February at just past Full phase in Leo. Relatively high in the sky for those of us observing in the northern hemisphere and being just past Full Moon, naturally, this is not the best time for deep sky observations, or imaging faint objects without significantly narrowband filtration. 

 

The Moon reaches Last Quarter on the 7th, when resident in Libra. Our natural satellite comes together in conjunction with Jupiter on the morning of the 7th and 8th, the two objects sitting about 8 degrees from one another, low in the predawn sky - the Moon being the most northerly. It should be quite a beautiful sight and well worth a photograph, if you're an early riser. 

 

The Moon and Jupiter, dawn, 7th February.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

The Moon reaches New phase on February 15th, when it joins the Sun in Capricornus, making the mid-month period ideal for deep sky imaging and observation. 

 

After this point in the month, the Moon rises north in the ecliptic, tracking through Capricornus, Aquarius, Pisces and Cetus, until it reaches First Quarter in Aries on the 23rd. Although February may not feel like Spring - we're approaching the time of the year where for those of us in higher northern latitudes, the Moon at Waxing Evening Crescent phase appeared highest in the sky.  These  phases are the "High Spring Crescents" much beloved of Lunar observers in these parts of the world. While February's evening crescent phase won't be quite as high in the sky at it's peak than those of the next 3 months, February's First Quarter should present a very good opportunity for observation of the Moon's eastern limb. 

 

The Moon then continues its journey through the northern part of the ecliptic as it heads towards Full Moon in early March. As January had two Full Moons - a "Blue Moon" month - this has robbed February as a calendar month of a proper Full Moon of its own. This is a reasonably rare event, but just a coincidence of timing, rather than anything scientifically significant. 

 

The Planets

 

Mercury

 

Mercury starts February as a morning object, in Sagittarius. At -0.6 mag and 4.9 arc seconds diameter), it is reasonably bright but exceptionally poorly placed for observation from the northern hemisphere. The reason for this is the planet's separation from the Sun, at an angle of a little over 11 degrees and the planet rising in a particularly shallow part of the ecliptic, from a northern hemispherical perspective. At this point in time, Mercury sits just over 1 degree high in altitude from the horizon in the SE at sunrise (from 51 degrees N), making it impractical to spot before dawn. As is always the case with Mercury, things don't stay this way for long. 

 

Mercury comes to superior conjunction with the Sun on the 17th, rendering it unobservable. 

 

By the end of the month, Mercury has reemerged on the evening side of the Sun, sitting at -1.3 mag. The innermost planet has increased its separation from the Sun to just under 9 3/4 degrees and is now sitting in Aquarius, at a much less shallow angle in the ecliptic (from the temperate northern hemisphere) than it did at the month's beginning. Mercury stands around 8 degrees high at sunset (from 51 degrees N), which will make observations practical from most parts of the world - though observers are aided in their attempts to locate Mercury by the much brighter Venus, which sits a degree and a half to the NW on the 28th. 

 

 Mercury and Venus, sunset, 28th February.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.


Venus

 

At the beginning of the month, Venus is to be found 5 3/4 degrees from the Sun and stands just under 3 degrees high in the west at sunset (from latitude 51 degrees N). The planet's proximity to the Sun will mean it remains a challenging target to say the least, despite its -3.9 mag brightness. 

 

By mid-month, Venus' brightness remains static, but it has increased its separation from the Sun to over 9 degrees and now stands 6 degrees high in Aquarius, in the west at sunset (from latitude 51 degrees N). 

 

By the end of February, Venus remains at -3.9 mag, showing a 10 arc second diameter, 98% illuminated disk. By this point it has crept north in the ecliptic from a northern hemispherical perspective and now stands over 9 degrees high at sunset (again, from latitude 51 degrees N). The planet is now separated from the Sun by just over 12 degrees. 

 

 

Mars

 

Mars starts the shortest month in Scorpius, at a brightness of +1.2 mag. It's angular size is now 5.6 arc seconds across and it stands 18 1/3 degrees high in the south at sunrise (from latitude 51 degrees N). While Mars isn't at its best at the current time, we're now catching the planet up on our faster interior orbit. While Martian opposition is still some way off in July, the trend is definitely upwards in terms of brightness and angular size. 

 

By mid February, Mars has brightened to +1.0 mag and presents a 6.1 arc second angular diameter. It stands just under 17 degrees high at sunrise (from latitude 51 degrees N). 

 

At the end of February, Mars is now found in Ophiuchus and has brightened to +0.8 mag. It is now 6.6 arc seconds in angular diameter. The Red Planet stands just under 16 degrees high, almost due south at daybreak (again, from latitude 51 degrees N). 

 

Mars, dawn, 28th February.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

Jupiter

 

February 1st finds Jupiter in Libra at -2.0 mag, 35.8 arc seconds diameter and standing 21 1/2 degrees high at transit point, which it reaches at 6.31am (GMT). The planet rises at just before 2am local time (from 51 degrees N).

 

Jupiter GRS and Io Transit, 5.46am, February 6th.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.

 

Mid-month finds Jupiter much the same: it has brightened somewhat to -2.1 mag and is now 37.3 arc seconds diameter. The King of the Planets now rises at 1.13am (GMT) and transits a little before sunrise at 5.45am, when it stands 21 1/3 degrees high in the south (from 51 degrees N).

 

The end of the shortest month sees Jupiter at -2.2 mag. The planet rises at 12.22am (GMT) and transits at 4.52am, when it will attain a height of just over 21 degrees in the south (from 51 degrees N).

 

Saturn

 

Saturn is a morning target in Sagittarius during February, rising at a little after 5.30am (GMT, from 51 degrees N) and stands 11 3/4 degrees high in the SSE at sunrise. At +0.6 mag, Saturn isn't especially prominent, but still brighter than any star in its resident constellation. It is separated from the Sun by 37 1/2 degrees on the 1st. 

 

By the end of the month, nothing much has changed as far as Saturn's concerned: the planet is still +0.6 mag and 15.8 arc seconds across. It now stands 14 1/2 degrees high at sunrise (from 51 degrees N).

 

 

Uranus and Neptune

 

Uranus and Neptune are both early evening targets as February begins, in Pisces and Aquarius respectively. At +5.9 magnitude and 3.5 arc seconds diameter, Uranus is definitely the easier target and is technically a naked eye object - though you will need an exceptional observation site, good eyesight and very favourable atmospheric conditions to spot it without optical aid. Binoculars or a telescope provide a much better chance to find the planet, which appears as a green-gray disk in telescopes. Uranus is found in the central "V" of Pisces and transits around 4pm (GMT, from 51 degrees N) during the middle of the month, setting at a little before 11pm. Being further east in the ecliptic than Neptune is, Uranus is better placed for observation than its neighbour. 

 

Uranus and Neptune, early evening, 15th February.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.


Neptune, at +8.0 magnitude is fainter and subsequently much more tricky. Being closer to the Sun than Uranus, it offers a much shorter window for observation in the very early part of the month. However, Neptune is headed towards superior conjunction (the opposite side of the Sun, as it appears from Earth) in early March and will be lost in the evening twilight as February continues. Neptune and Venus are in conjunction with one another on the evening of the 21st, when they are separated by about half a degree, though due to their proximity to the Sun and the horizon, Neptune will be extremely challenging to spot, even if Venus isn't. 

 

 Neptune and Venus, 21st February (blue circle represents a 2 degree field).  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.



Comets

 

There are no reasonably bright comets predicted to be observable during February (at time of writing).  However, we have the distinct probability of three naked eye comets during 2018 - the recently discovered comet Pan STARRS 2017 S3, which should reach a peak in August/September, and the return of periodic comets 21P/Giacobini-Zinner (which could reach mag 4 in August/September) and 46/P Wirtanen (which is due to reach low naked eye visibility in the latter part of the year, peaking in December for those in the northern hemisphere).  As ever, there’s always the chance of new comets being discovered, or know ones having outbursts of brightness.  We’ll naturally keep you posted in regards to future developments we receive them.

 

 

Deep Sky Delights in Gemini, Cancer and Northern Monoceros

 

This month we turn our attention to the two neighbouring Zodiacal constellations of Gemini and Cancer - and the northerly part of Monoceros, which sits below Gemini.  These constellations - particularly western Gemini and Monoceros - sit on or close to the plane of the Milky Way and are subsequently home to some wonderful star clusters and nebulosity, which are easily observable with amateur telescopes and binoculars.

 

Gemini, Cancer and Northern Monoceros.  Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.


Of the two zodiacal constellations, Gemini, the twins, is by far the most prominent to the naked eye, containing a good deal more in the way of bright stars.  Castor, (Alpha Geminorum), is a fine double star and an easy target in small instruments.  Consisting of two stars, A and B, of +2 and +2.9 mag respectively, Castor's elements are currently widening and are separated by 4.5-5 seconds of arc.  Castor's double nature was discovered in 1678 by Cassini (he of Saturn's ring division fame, amongst many other discoveries) and bears the distinction of being the first gravitationally bound object to be identified beyond the reaches of the Solar System.  Castor A and B's orbit about a mutual gravitational point takes around 467 years to complete, but both stars are also in turn doubles, with much fainter M-class dwarf companions.  In addition to these companions there is also present in the system a further pair of gravitationally bound M-class stars.  This makes Castor not just a double star, but a sextuple - quite a collection!  Sadly, only the primary elements are observable in amateur instruments.

 

To the Westerly reaches of Gemini, is to be found M35.  M35 is a very prominent star cluster, at +5 mag, easily picked in small telescopes and binoculars and can also be seen with the naked eye from a reasonable site.  Consisting of well in excess of 100 observable stars (mags 6-13th), M35 was first noted by Astronomer Philippe Loys de Cheseaux in 1745.  Also included in the Uranographica Britannica by John Bevis in 1750, M35 was catalogued by Messier in 1764, who credited Bevis with its discovery.

 

M35.  Image Credit: Atlas Image [or Atlas Image mosaic] obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. Public Domain.


Many of the 100+ observable stars are types G and K stars - similar in class to our Sun- though these seem to be of a considerably larger mean size than main sequence.  M35 is tentatively aged at about 100 million years - about the age of the nearby M45, (the Pleiades) though problematically, stellar evolution is thought to be considerably more advanced in the case of M35.  Does this mean that M35 is in fact older, or are the Pleiades actually younger?  Further observation and theories will be needed to explain this anomaly.   

 

In the background sky to M35 lies the fainter (+8 mag) open cluster NGC2158, though this is nearly six times further away than M35's 2800 light years. In addition to this, there is also the yet fainter and more compact IC2157 cluster (+8.4 mag) - making this an extremely rich area for sweeping with virtually any type of optical aid.

 

Drifting Eastward, 2 1/3 degrees East of the star Wasat (Delta Geminorum) is the fabulous Eskimo Nebula, NGC2392.  This Planetary Nebula supposedly resembles an Eskimo's head, surrounded by the fur of an Arctic Parka hood.  A reasonably compact 0.8 arc minute across (about 2/3rds the size of the Ring Nebula, M57), the Eskimo is only +9.19 mag, though its compact size makes its surface brightness quite high and it takes magnification well.   Discovered by William Herschel in 1787, it is perhaps surprising that it wasn't noticed by earlier observers - though this is most likely down to its small size.  OIII filters reveal more of the two stages of the object: it's tenuous outer shell and the gleaming, brighter interior.  Larger instruments reveal more of the complex structure of the internal part of the Eskimo -  its radial double shell of expanding gasses and fine filaments blown by cosmic winds form its central star.  This central star shines at +10.5 mag and is relatively easy to spot in most instruments.   The nebula is thought to lie at 2800-3000 light years distance.

 

The Eskimo Nebula, Hubble Image.  Image Credit: NASA/ESA.  Public Domain.

 

Further South from the Eskimo is another older, larger and fainter object - The Medusa Nebula (Abel 21).  Whereas the Eskimo is small and comparatively bright, the Medusa is large - at 10 arc minutes across it is a third the diameter of the Full Moon.  Telescopes of 8-inches + aperture, coupled with a good OIII filter and a dark site will be needed to seen the Medusa.  Although listed as being +10.19 mag, this is spread out over a significant area of sky, so it is in long duration astrophotography that the wonders of the Medusa really start to reveal themselves.  A modest aperture telescope will be needed and a sturdy equatorial mount, capable of being autoguided , will be needed to attempt to image this object.  Images reveal the serpent-like tendrils of nebulosity that give this mysterious object its name - its namesake Medusa being the Gorgon who had snakes for hair in classical Greek mythology.  The stare of Medusa was reputed to turn people to stone, though staring at this nebula through a large telescope will be a much more pleasant experience…  The Medusa lies about half the distance from us as the Eskimo Nebula - 1500 light years and is around 4 light years in diameter.  Opinions were divided on the true nature of the Medusa: George Abel, its discoverer thought it to be an old planetary nebula, whereas many considered its irregular nature to indicate it was a supernova remnant.  Narrowband imaging has revealed the true extent of the Medusa's helical hourglass figure - making it much more likely to be, as Abel initially suggested, a planetary nebula.

 

The Medula Nebula.  Image Credit: Joel Schuman, Mt Lemmon Observatory, Creative Commons.

 

Moving in a southerly direction, across the constellation border into Monoceros, the Unicorn, we come to the beautiful Cone Nebula and Christmas Tree Cluster, NGC2264.  The nature of the two objects and their relationship is problematic to define.  The nebulosity's distance is sometimes put at 1000 light years hence, whereas the cluster is considerably further away at 2200 light years away (Clearly too far a distance removed to be easily defined as related), other sources but both objects being at 2700 light years away.  Visually, it certainly looks as if the cluster is emerging from the nebulous region - if they are not related, they are doing a very good impression of being so!  The two objects take up a large area - almost a Full Moon's width wide by two long (in actual fact the nebula extends much further but is largely invisible).  Although listed as a bright object with the combined visual magnitude of +3.9 mag, large apertures and favourable observing conditions are needed to glimpse the nebulosity, though the cluster is easy enough with many instruments.  The "Cone" feature of the nebula is to be found to the Southerly end of the object and is a darker lane of gas and dust silhouetted against the brighter background nebula and star field.  Long duration imaging is needed to see this feature well, as it can be difficult to detect visually,  The Christmas Tree and the Cone were first noted by William Herschel in 1784 and 1785 respectively.  The nebula, as noted, extends further and is also supposedly related to other objects in this area.

 

The Cone Nebula and Christmas Tree Cluster.  Image Credit: Mark Blundell.

 

Four degrees south of NGC2264 is the spectacular Rosette Nebula and Cluster system, comprising NGCs 2237, 2238, 2239, 2244 and 2246.  The Rosette's central cluster NGC2244 is easily seen in binoculars and small telescopes and is no challenge to larger instruments whatsoever - this was discovered by the first Astronomer Royal, John Flamsteed in the early 1690s.  The nebulosity surrounding the cluster is slightly trickier and while it can be seen with larger binoculars from a very dark site, requires a larger instrument of the 8-inch + class to resolve well.  Variations and the darker lanes in the nebulosity are best seen with more substantial telescopes, using filtration - UHC, OIII and H Beta Filters all help isolate differing areas of the Rosette. This nebulosity will also require a low power widefield eyepiece as the extent of the Rosette Nebula is huge: 80 x 60 arc minutes, over 5 times the area of the Full Moon.  The nebulosity was first noted by 19th Century Astronomers John Herschel, Albert Marth and Lewis Swift.  The Rosette's 30 light year wide central hole has been created by the solar wind from the stars of NGC2244, this wind has created compression fronts in the outer nebula, leading to the Rosette's radial petal-like appearance.  Astrophotography will reveal the whole of the Rosette's structure and its deep pink and red colouration.

 

The Rosette Nebula.  Image Credit: Mark Blundell.

 

Drifting north and east, we came to the zodiacal constellation of Cancer is not a particularly prominent constellation, comprising as it does of stars no brighter than the 3rd magnitude.  Of its principle stars, Iota Cancri is probably the most interesting for amateur observers.  This star marks the most Northerly point of the main constellation and is a double star  of +4.01 and +6.57 mags.  The primary star is a yellow G-type star, the secondary a white A-type main sequence star.  Separated by 30 seconds of arc, these are an easy and attractive pair for small telescopes.  The angular separation of the two has not changed radically for over a century, but it has been established the two are related.  It is estimated their orbital period is over 65,000 years.

 

Nine degrees to the South of Iota Cancri lies one of the jewels of the night sky, the bright, expansive open cluster of M44, The Beehive or Praesepe.  At +3.09 mag this cluster is an easy naked eye object from a reasonable observing site and at over a degree in size, is pretty unmissable!  Recognised since antiquity, M44 was known as Phatne - "The Manger" to the ancient Greeks (Praesepe being the Latinised translation of this title), though its first datable mention in literature came in 260 BC, when the Greek poet Aratos called it the "Little Mist". M44 was also contained in Hipparchus' star catalogue of 130 BC.  The Beehive as a name seems apt, as the core of M44 could be argued to resemble a natural hive, with outlying stars being "the Bees" hovering around it.

 

The Beehive.  Image Credit: Miguel Garcia.  Creative Commons.

Containing over 1000 individual stars (over 75 of which are observable to the smallest amateur telescopes), M44 appears to share a proper motion with the Hyades in neighbouring Taurus, which seems to suggest a common point of origin.- both clusters seem to be of a similar age too (around 600-730 million years).  The Beehive lies 570-610 light years away from us and is estimated to be about 12 light years in diameter (though its tidal influence reaches much further).  This cluster should be seen by everyone - just grab a pair of binoculars.  Its mix of stellar components make for a lovely imaging opportunity too.

 

Eight degrees to the South East of the Beehive, another open cluster, M67, is to be found.  Although fainter and more compact that M44 at +6.90 mag and 25 arc minutes, it is in its way as attractive a target as its neighbour.  Discovered by Johann Koelner in the late 1770s, M67 was catalogued by Messier in 1780.

 

Comprising of about 100-or-so observable members (out of a total of over 500 stars), many of which are similar it class to the Sun, M67 is one of the oldest clusters in our galaxy.  It is thought to be around 4 billion years old - nearly as old as our own Sun and lies 3000 light years away.  M67 does also contain some "blue stragglers" - stars that technically speaking it should not contain.  Whether these have been swept up by M67 during its journey around our galaxy or not is a question that, to date, remains unanswered.  Observers using higher power magnifications will resolve some spectacular chains of stars in M67.  It truly is a lovely object.

 

Further Southeast (by just under 7 degrees) from the delights of M67 is a much more challenging target, the beautiful spiral galaxy NGC2775.  Though not intrinsically conspicuous at +10.10 mag, it is a compact target at 4.3 x 3.3 minutes of arc and has a comparatively bright core.  Lying some 60 million light years away, NGC2775 is an exotic blend of a spiral structure and large elliptical core, which itself is ringed by pronounced hydrogen regions.  The arms of the outlying spiral sections are very finely structured, though this is only really visible in long duration images.  Visually, NGC2775 is visible with a reasonable-sized instrument, though a larger scope may on occasion show interactive stream of material from NGC2777, which is tidally interacting with its larger neighbour.  Whilst a challenge, NGC2775 has been the site of some 5 Supernovae since the mid-1980s, so who knows what you may find there?

 

NGC2775, HST composite image.  Image Credit: NASA/ESA.  Public Domain.

Cancer contains many galaxies between the +12-14 mag range. Being located so close to the Leo, Leo Minor and Hydra galaxy clusters, it would seem a fairly safe assumption that Cancer's galaxies are gravitationally clustered.  Studies of proper motion based on spectral shift have confirmed, however, that these galaxies are not related.  Still, there is much for owners of large telescopes and astrophotographers to enjoy galaxy-wise in Cancer.  Although many of these objects are challenging and are not as easily-observed as those in the adjacent constellation of Leo.

 

Text: Kerin Smith