the summer night sky - cosmic river · greco-egyptian writer known for his works in ... from greek...

The Summer Night Sky

Stars and constellations

Dr Adrian Jannetta FRAS

The Summer Night Sky 1 / 31 Dr Adrian Jannetta FRAS

THE SUMMER NIGHT SKY

Summer observing in Northumberland can begin from Augustonwards. Astronomical darkness (when the Sun is more than 18◦

below the horizon) begins from the first week of August.

The Summer Triangle

Along the Milky Way: from Cygnus to Sagittarius

Deepsky objects for binoculars and telescopes

Brief history of the 88 constellations


CONSTELLATIONS

Traditional Romanian Arabic

Humans are pattern seekers! We can see patterns and shapes among the random distribution ofnearby bright stars. Many cultures around the world have had their own traditions for naming thestar patterns they see; many are tied in with history and mythology.


PTOLEMY’S 48 CONSTELLATIONS

Claudius Ptolemy (c.AD 90 — AD 168) wasGreco-Egyptian writer known for his works inastronomy, astrology, mathematics andgeography.

Ptolemy’s major astronomical contribution washis Magna Syntaxis (the Great Treatise) which isbetter known by its later Arabic title: Almagest.

In the Almagest Ptolemy summarisesastronomical and mathematical knowledge ofhis day. He discusses the motion of the Sun,moon and planets and argues for anEarth-centred universe (geocentric model).

Within the pages of the Almagest are acatalogue of 1022 stars grouped within 48constellations. These patterns form the basis ofthe 88 modern constellations.


SUMMER TRIANGLE

CYGNUS

PEGASUS

LYRA

HERCULES

OPHIUCHUS

CEPHEUS

LACERTA

AQUILA

AQUARIUS

DRACO

SCUTUM

SAGITTA

VULPECULA

DELPHINUS

EQUULEUSSERPENS C

AUDA

Ð

×

Ø

Ð

Õ

Ù

Ø Ó

Ö

18h

19h20h21h

22h

�10�

0�

+10�

+20�

+30�

+40�

+50�

+60�

Altair

Vega

Deneb

The Summer Triangle is an asterism ofthree bright stars. Popularised byPatrick Moore and H.A. Rey since the1950s but has origins in several early20th century astronomy texts.

Vega (α Lyrae, mag +0.0) is thebrightest and ~25 light-yearsway.

Altair (α Aquilae, mag +0.2) is~17 light-years away.

Deneb (α Cygni, mag +1.3) is~2600 light-years away.

The Summer Triangle is visible formost of the year at some part of thenight!

It is high in the southern sky duringevenings in the summer and autumn.


DEEPSKY OBJECTS: AN INTRODUCTIONNebulas are clouds of gas and dust. Emission nebulaeshine because of energetic processes inside them (e.g.star formation). Reflection nebulae shine because theyilluminated by nearby stars. Dark nebulae are silhouettedagainst a brighter background of stars.

Open clusters are loosely gravitationally bound systemsstars. They formed from the same nebula and maycontain tens, hundreds or thousands of stars. Openclusters have formed throughout the life of the Galaxy.

Globular clusters are strongly bound systems stars.They formed from the same nebula and may containhundreds of thousands or millions of stars. Globularclusters formed at the same time as the Galaxy.

Galaxies are the most distant objects that amateurastronomers can view with telescopes. They are islandsof stars (containing many hundreds of billions of them issome cases). They come in many shapes and sizes.


CYGNUS, THE SWAN

Cygnus may represent one or more swansfrom Greek mythology.

In one story, Zeus transformed himself intoa swan in order to seduce Leda, the wife ofthe Spartan king.

In another legend, Orpheus wastransformed into a swan after his murder.He was placed among the stars next to hislyre (the constellation Lyra).

The Milky Way is particularly rich inCygnus and a prominent dust lane (theCygnus Rift) seems to split it into twostreams. There are countless open clustersand bright (photographic) nebulae inCygnus.


CYGNUS STAR MAPDeneb (α Cygni) is an extremely luminousblue-white supergiant star estimated to be 2600LY away.

Albireo (β Cygni) is a showpiece double star forsmall telescopes. Bright yellow/orange primarywith a fainter bluish companion.

χ Cygni is an unstable red giant varying inbrightness between 3rd and 14th magnitudesover a period of roughly 407 days.

61 Cygni was the first star to have its distancemeasured by parallax (Bessel, 1838). It is 11light-years away.

M 29 and M 39 are notable open clusters visiblewith binoculars.

NGC 6826 is a planetary nebula known as theblinking planetary; it looks like a star untilviewed with averted vision!

NGC 6960/92/95 is a supernova remnant knownas the Veil Nebula. Visible easily with a nebulafilter; otherwise a big telescope required!

NGC 7000 is a large emission nebula near Deneb.Visible in telescopes with nebula filters.


OBJECTS IN CYGNUS

Albireo; two stars of 3rd and 5th magnitudeseparated by 34 arcseconds.

NGC 7000 — North America Nebula. Anemission nebula near Deneb.


OBJECTS IN CYGNUS

M 39 is a 5th magnitude open cluster in Cygnus. It appears as a misty condensation inthe Milky Way through binoculars. Telescopes show dozens of stars scattered over anarea the size of the full moon.


LYRA, THE LYRE

Lyra is a small constellationrepresenting the lyre of Orpheus.

According to the Greek myth,Orpheus was a musician who waskilled by the Bacchantes. After hisdeath, his lyre was thrown into theriver; Zeus sent an eagle toretrieve the lyre, and ordered bothof them to be placed in the sky(the eagle is neighbouring Aquila).

Lyra is adjacent to the Milky Wayand contains a few star clustersand a notable planetary nebula.


LYRA STAR MAPVega (α Lyrae) is a bright, white main sequence starshining at magnitude 0 and only 25 light-years away.

Sheliak (β Lyrae) appears as a single star to telescopesbut is actually a semidetached binary star! Moreoverthe stars eclipse each other every 13 days causing thebrightness to vary between +3.4 and +4.6.

δ Lyrae is an easy optical double star(binoculars/telescopes) consisting of a 4th magnitudered giant and a fainter 6th magnitude blue giant. Thetwo stars are part of a scattered cluster calledStephenson 1.

ε Lyrae is one the most celebrated multiple stars in the

entire sky. Close to Vega, binoculars split ε1 and ε2

easily. Larger telescopes will resolve each of those intoa binary system. For that reason it also known as theDouble Double!

M 56 is an 8th magnitude globular cluster visible as afuzzy patch in small telescopes. About 33,000light-years away.

M 57 is a showpiece planetary nebula. Telescopes atmodest magnification show a diffuse oval ring of 9thmagnitude. The central star is beyond the reach ofmost amateur telescopes; it is a white dwarf star of~16th magnitude.


OBJECTS IN LYRA

The Double Double.

Left: widefield view of the region around Vega; epsilon Lyrae is easily split as a double star. Right:

high power view through a 6 inch telescope. Each component of consists of two stars. The ε1 pair

are 2.5 arcseconds apart. The ε2 pair are 2.4 arcseconds apart.


OBJECTS IN LYRA

M 57 — the Ring Nebula. This is a fine example of a planetary nebula; the end of life for a mainsequence star. The core of the old star remains in the centre; it is a white dwarf star. M 57 is about1,300 light-years away.


OBJECTS IN LYRA

Sheliak (β Lyrae) is a semidetached binary star whose components orbit each other so closely thatthey tidally distort each other. Although they cannot be split with amateur telescopes, the pair wereresolved at infrared wavelengths for the first time by the CHARA Array interferometer in 2005.


AQUILA, THE EAGLEAquila is a prominent constellationrepresenting an eagle.

According to one Greek myth, Zeussent the eagle to carry off Ganymede,a shepherd boy from Phyrgia. Zeuswanted Ganymede to be hiscup-bearer because his daughter Hebehad messed up by dropping it at animportant ceremony.

In another story Aquila is the eaglesent to retrieve the lyre of Orpheus. Inanother the eagle is used by Zeus topunish Prometheus for giving fire tohumans.

Aquila lies on the celestial equatorand the constellation is rich with faintstar clusters because the Milky Wayflows through it.


AQUILA STAR MAPAltair (α Aquilae) is white main sequence starwith a magnitude of +0.9. It is one of the neareststars to us in the sky — just 17 light-years away.It is perhaps made more obvious in the sky bybeing flanked by two fainter stars to the northand south: Tarazed and Alshain.

ρ Aquilae moved across the border intoDelphinus in 1992.

15 Aquilae is an easy to split double star forsmall telescopes. The colours contrast nicely:amber/yellow with blue. The components areseparated by 39 arcseconds.

57 Aquilae is an easy double star for smalltelescopes. The two components are roughly 6thmagnitude and separated by 35 arcseconds.

NGC 6760 is an 9th magnitude globular cluster.Visible as a misty patch through small telescopes;larger instruments will begin to resolve the outerregions into stars.

NGC 6790 is an 10th magnitude planetarynebula. It appears as a faint blue-green star atlow magnification with a high magnificationneeded to see the disk shape.


SAGITTA, THE ARROW

According to Greek mythologySagitta represents the arrow firedby Hercules to kill the eagle(Aquila) which perpetuallyknawed the liver of Prometheus (apunishment sanctioned by Zeusfor Prometheus giving fire tohumans!)

Sagiita is one of the smallestconstellations in the sky (it ranks86/88 in terms of area) and is oneof the original 48 constellationsintroduced by Ptolemy. It islocated slightly north of thecelestial equator and is visiblefrom everywhere in the worldexcept central parts of Antarctica.


SAGITTA STAR MAP

γ Sagittae is an orange giant star and thebrightest star in the constellation (mag. +3.5)

θ Sagittae is a beautiful triple star for smalltelescopes. The central pair of stars are of 6th and9th magnitudes and separated by 12 arcseconds.The third star is around 7th magnitude andwidely separated from the other two (89arcseconds). The stars are all unrelated — just achance alignment.

M 71 is a globular cluster and one of thehighlights of the northern summer night sky.Visible as a misty patch through binoculars.Telescopes at modest powers will resolve stars tocore of the cluster. M 71 is in rich part of theMilky Way; the field of view is filled withforeground stars!


OBJECTS IN SAGITTA

M 71 is a globular cluster situated about 12,000 light-years from us. The cluster is much moreloosely defined than other objects of the same type and until the 1970s it was actually classed as anopen cluster.


MODERN CONSTELLATIONS

The current list of 88 constellations was recognised by the International AstronomicalUnion in 1922.

The modern list includes the 47 constellations from Ptolemy’s Almagest.

A further 41 constellations were added to fill in gaps between Ptolemy’s constellationsand to cover the large region around the south celestial pole which Ptolemy (andothers) couldn’t see from the Mediterranean:

Caspar Vopel; 1 constellation in 1536

Petrus Plancius; 4 southern constellations in 1597/8.

Pieter Dirkszoon Keyser and Frederick de Houtman; 12 constellations in 1603

Johannes Hevelius; 7 constellations in 1690.

Nicolas Lacaille; 14 constellations in 1752. He also split Ptolemy’s Argo Navisconstellation into three new constellations.

Constellation boundaries were fixed in 1930 by an IAU subcommittee led by EugèneDelporte. He ended the practice of constellations with shared stars. He based hisboundaries for the 1875 epoch. Precession of the equinoxes is gradually shiftingborderline stars into adjacent constellations.


VULPECULA, THE FOX

This constellation was introduced byJohannes Hevelius in 1690. It wasoriginally named Vulpecula cum ansere(little fox with the goose) and was initiallydepicted as a fox running with a goose inits jaws.

Vulpecula is located between Cygnus andSagitta. It is a faint constellation — no starsare brighter than fourth magnitude. TheMilky Way runs through the constellation,perhaps adding to the difficulty ofidentifying the stars of Vulpecula.

Despite the obscure nature of theconstellation, it contains a number ofinteresting objects for binoculars and smalltelescopes.


VULPECULA STAR MAP

Anser (α Vulpeculae) is an orange giantstar about 300 light-years away. Binocularsshow a close 6th magnitude companionabout 7 arcminutes away; an easy opticaldouble.

M 27 is one the brightest planetary nebulasin the entire sky. It is visible as a tinydiffuse disk of 7th magnitude withbinoculars and small telescopes.

Cr 399, also called Brocchi’s Cluster, is astriking asterism of stars best seen throughbinoculars. A straight line of stars with ahook shape coming from the middle.Nicknamed the Coathanger.

NGC 6960 is a large scattered open cluster.About 60 stars scattered over an area thesize of the moon.


OBJECTS IN VULPECULA

M 27 / the Dumbbell Nebula is abright planetary nebula. Distance isestimated to be 1,360 light-years. Thecentral star is the largest knownwhite-dwarf.

Collinder 399 / Brocchi’s cluster isalso called the Coathanger. Thisasterism is a chance alignment of stars.


SCUTUM, THE SHIELD

Scutum is a small constellation to the southof Aquila. It was introduced in the 17thcentury by Johannes Hevelius. The originalname of the constellation was ScutumSobiescianum (the shield of Sobieski) tocommemorate the victory of the Christianforces led by Polish King John III Sobieski(Jan III Sobieski) in the Battle of Vienna in1683.

Scutum is faint pattern of stars and onlyone is brighter than 4th magnitude. TheMilky Way is particularly rich as it passesthrough Scutum and there are manyobjects of interest for amateur astronomerswithin the borders.

The spacecraft Pioneer 11 is heading in thedirection of Scutum; although it will notpass close to any of the stars for many tensof thousands of years.


SCUTUM STAR MAPα Scuti (mag +3.9) is an orange giant star about175 light-years away.

δ Scuti is an 5th magnitude orange giant stararound 200 light-years away. It is variable starwhich pulsates in multiple directions and is theprototype of an important class of variables usedto determine distances in the universe.

UY Scuti is a supergiant star about 9,500light-years away. It is currently the largest starknown to astronomers. UY varies a little but isaround 10th magnitude.

M 11 is superb open cluster for small telescopes.The cluster is around magnitude +5.8 making itan easy target for binoculars and small telescopes.A fan shaped splash of around 3000 stars with abright leader at the tip of the fan. The shape givesrise to its nickname: the Wild Duck Cluster.

M 26 is an 8th magnitude open cluster best seenthrough medium sized telescopes.

NGC 6720 is an 8th magnitude globular cluster.This cluster passed through the plane of thegalaxy just a few million years ago and gravityseems to be stripping the cluster of its lowestmass stars.


OBJECTS IN SCUTUM

UY Scuti; a candidate for the largest star in theMilky Way. Visible with small telescopes in therich starfields of Scutum.

M 11, the Wild Duck Cluster. One of the moststriking open clusters in the night sky; about 3000stars at a distance of 6000 light-years.


SAGITTARIUS, THE ARCHER

Sagittarius is one of Ptolemy’s original 48constellations. Sagittarius is a centaur (partman/part horse) usually depicted with abow and arrow. In some stories herepresents Chiron, pointing the way forJason and the Argonauts on their quest tothe golden fleece.

Sagittarius is a zodiac constellation; theSun passes through its borders betweenDecember 18th and January 18th each year.

The centre of the Milky Way is foundwithin Sagittarius and the constellation isrich with all kinds of deepsky objects.

Unfortunately, Sagittarius doesn’t risecompletely above the UK horizon and thestars that do are always seen at lowaltitude in the southern sky for just a fewhours each evening.


SAGITTARIUS STAR MAPKaus Australis (ε Sagittarii) is the brightest starin the constellation but not easy to see from theUK. It is a white star coming to the end of its timeon the main sequence.

β1β2 Sagittarii is an easy optical double star forthe naked eye. Two nearly equally bright stars ofmagnitude 4. Not visible from the UK.

M 8 (Lagoon nebula) is a giant interstellar cloudand emission nebula visible with binoculars andsmall telescopes. Another nebula (M 20 Triffidnebulae) lies nearby to the north.

M 17 (Omega, or Swan or Horseshoe) is a brightnebula near the border with Serpens. It is one ofthe brightest and most massive sites of starformation in the Milky Way.

M 24 is a distant swathe of spiral arm seenthrough a transparent window in the interveningdusty material. Tens of thousands of stars acrossa deep volume of the Milky Way. Easy naked eyefeature about 1.5◦ in length.

NGC 67120 is an 8th magnitude globular cluster.This cluster passed through the plane of thegalaxy just a few million years ago and gravityseems to be stripping the cluster of its lowestmass stars.


OBJECTS IN SAGITTARIUS

M8 — The Lagoon Nebula. A giant star forming region about 4000 light-years away. Credit:"Lagoon Nebula (ESO)" by ESO/S. Guisard.


the summer night sky - cosmic river · greco-egyptian writer known for his works in ... from greek...

Documents