APOD: Messier 45: The Daughters of Atlas... (2019 Nov 07)

[APOD Robot]

Messier 45: The Daughters of Atlas and Pleione

Explanation: Hurtling through a cosmic dust cloud a mere 400 light-years away, the lovely Pleiades or Seven Sisters open star cluster is well-known for its striking blue reflection nebulae. It lies in the night sky toward the constellation Taurus and the Orion Arm of our Milky Way Galaxy. The sister stars and cosmic dust cloud are not related though, they just happen to be passing through the same region of space. Known since antiquity as a compact grouping of stars, Galileo first sketched the star cluster viewed through his telescope with stars too faint to be seen by eye. Charles Messier recorded the position of the cluster as the 45th entry in his famous catalog of things which are not comets. In Greek myth, the Pleiades were seven daughters of the astronomical Titan Atlas and sea-nymph Pleione. Their parents names are included in the cluster's nine brightest stars. This deep and wide telescopic image spans over 20 light-years across the Pleides star cluster.

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[Ann]

Who isn't happy to see the Pleiades as an APOD?

And I for mine am very happy to see Adam Block get another APOD!

This particular picture of the Pleiades is very deep and wide, and it reveals lots of nebulosity outside the most recognizable outline of the Pleiades. The nebulosity comes in different colors, yellowish, faintly reddish, and blue. Most of the blue nebulosity that is disconnected from the recognaizable outline of the Pleiades is seen to the left of the Pleiades in this picture (actually to the north of this iconic cluster).

Fascinatingly, though, the star that is most deeply immersed in blue nebulosity outside the Pleiades (a star at 8 o'clock) has a much larger parallax than the stars of the Pleiades. Judging from its parallax, this star, HD 23985, is less than half as far away as the Pleiades, less than 200 light-years for this star versus more than 400 light-years for the Pleiades!

Fascinating! Do I take this to mean that the dust cloud that the Pleiades are immersed in is more than 200 light-years deep? So that the Pleiades and HD 23985 are immersed in different ends of one admittedly somewhat broken huge dust cloud?

Apart from HD 23985, most of the blue stars in Adam Block's picture have similar parallaxes and similar proper motions as the most iconic Pleiades. So the actual Pleiades cluster extends well beyond its most iconic outline.

The Pleiades small.png (352.18 KiB) Viewed 3969 times

[orin stepanek]

7 Sisters; my favorite cluster!

[GeoX]

Nice uncommon view instead of the usual tight closeup!

[sillyworm 2]

Was just viewing this cluster in the deep ink black skies of upper lower Michigan.No street lights or light pollution on our block .Stunning.

[TheZuke!]

Subaru!

[BDanielMayfield]

Was just viewing this cluster in the deep ink black skies of upper lower Michigan.No street lights or light pollution on our block .Stunning.

As you look at them with unaided eyes, how many of them can you see? Then, look at them with binoculars or a small telescope.

I've heard that most people see less than 7 these days. Has one of the sisters faded or is it just modern light pollution?

[Chris Peterson]

Was just viewing this cluster in the deep ink black skies of upper lower Michigan.No street lights or light pollution on our block .Stunning.

As you look at them with unaided eyes, how many of them can you see? Then, look at them with binoculars or a small telescope.

I've heard that most people see less than 7 these days. Has one of the sisters faded or is it just modern light pollution?

I don't think the asterism has changed since people have been observing it. People picked "seven" because that's a number most cultures placed mystical significance on. Most people under typical observing conditions see six stars. Under good, dark skies and with excellent vision, most people see eight or nine stars. But few see seven.

[sillyworm 2]

I see it pretty clearly with unaided eyes.Sure I have to squint and I know there are at least 7 or 9 by it's apprearance...I actually did pull out a pair of binoculars a week ago.I could see the individual stars. It's a beautiful cluster.The space station flew right overhead back in Aug.

[Joe Stieber]

Was just viewing this cluster in the deep ink black skies of upper lower Michigan.No street lights or light pollution on our block .Stunning.

As you look at them with unaided eyes, how many of them can you see? Then, look at them with binoculars or a small telescope.

I've heard that most people see less than 7 these days. Has one of the sisters faded or is it just modern light pollution?

With unaided eyes from the New Jersey Pines (reasonably dark) on a moon-free night, I typically see five or six stars with casual observation. The most I've seen and counted with concentration on a good night is nine (9). I've actually seen more than that using averted vision, but couldn't count them -- as soon as I start to count, I involuntarily disrupt my averted vision. I suspect the vagaries of light pollution, atmospheric transparency and human vision could in themselves account variations in the number visible.

[Ann]

Was just viewing this cluster in the deep ink black skies of upper lower Michigan.No street lights or light pollution on our block .Stunning.

As you look at them with unaided eyes, how many of them can you see? Then, look at them with binoculars or a small telescope.

I've heard that most people see less than 7 these days. Has one of the sisters faded or is it just modern light pollution?

I don't think the asterism has changed since people have been observing it. People picked "seven" because that's a number most cultures placed mystical significance on. Most people under typical observing conditions see six stars. Under good, dark skies and with excellent vision, most people see eight or nine stars. But few see seven.

Well, seven "planets" in the night sky - the Sun, the Moon, Venus, Mars, Jupiter and Saturn - and therefore seven sisters of the Pleiades.

Ann

[TheZuke!]

As you look at them with unaided eyes, how many of them can you see? Then, look at them with binoculars or a small telescope.

I've heard that most people see less than 7 these days. Has one of the sisters faded or is it just modern light pollution?

As I am near sighted, all I see is a blur!

If one uses Orion's Belt as a line reference, Aldebaran is on the line to the west, with Subaru a bit beyond. and if they follow the "Belt line" to the East, Sirius awaits.

[TheZuke!]

Well, seven "planets" in the night sky - the Sun, the Moon, Venus, Mars, Jupiter and Saturn - and therefore seven sisters of the Pleiades.

Ann

And 7 days is approximately 1/4 of a Moon (month) cycle.
In the Old Testament, 7 was symbolic of "completeness", and 6 therefore, was "incomplete".
Which later, in the New Testament, 666 means "very incomplete".

TheZuke!

[BDanielMayfield]

Well, seven "planets" in the night sky - the Sun, ...

Ann

Seeing the Sun in the night sky, my oh my.

[neufer]

Well, seven "planets" in the night sky - the Sun, the Moon, Venus, Mars, Jupiter and Saturn - and therefore seven sisters of the Pleiades.

And 7 days is approximately 1/4 of a Moon (month) cycle.

In the Old Testament, 7 was symbolic of "completeness", and 6 therefore, was "incomplete".
Which later, in the New Testament, 666 means "very incomplete".

• That explanation is "very incomplete"
  (I've been told that 6 is a perfect number)

<<God took six days to create the world in the Old Testament Book of Genesis; humankind was created on day 6.

In the City of God, Augustine of Hippo suggested (book 11, chapter 30) that
God's creation of the world took six days because 6 is a perfect number.>>

• The age of the universe in Planck time ~ 8.08 x 10⁶⁰
  The largest perfect number proven by hand: 2¹²⁶(2¹²⁷-1) ~ 1.4474 x 10⁷⁶
  The approximate number of atoms in the observable universe ~ 8.68 x 10⁷⁹

Assuming the mass of ordinary matter is about 1.45×10⁵³ kg and assuming all atoms are hydrogen atoms (which are about 74% of all atoms in our galaxy by mass, calculating the estimated total number of atoms in the observable universe is straightforward. Divide the mass of ordinary matter by the mass of a hydrogen atom (1.45×10⁵³ kg divided by 1.67×10⁻²⁷ kg).

<<François Édouard Anatole Lucas (4 April 1842 – 3 October 1891) worked in the Paris observatory and later became a professor of mathematics in Paris. In the meantime he served in the army. In 1857, at age 15, Lucas began testing the primality of 2¹²⁷ − 1 by hand, using Lucas sequences. In 1876, after 19 years of testing, he finally proved that 2¹²⁷ − 1 was prime; this would remain the largest known Mersenne prime for three-quarters of a century. This may stand forever as the largest prime number proven by hand. Later Derrick Henry Lehmer refined Lucas's primality tests and obtained the Lucas–Lehmer primality test.

In 1875, Lucas posed a challenge to prove that the only solution of the Diophantine equation:

---

with N > 1 is when N = 24 and M = 70. This is known as the cannonball problem, since it can be visualized as the problem of taking a square arrangement of cannonballs on the ground and building a square pyramid out of them. It was not until 1918 that a proof (using elliptic functions) was found for this remarkable fact, which has relevance to the bosonic string theory in 26 dimensions.>>

<<In Greek isopsephy and Hebrew gematria, every letter has a corresponding numeric value. Summing these numbers gives a numeric value to a word or name. "Nero Caesar" in the Hebrew alphabet is נרון קסר‎ NRON QSR, which when used as numbers represent 50 200 6 50 100 60 200, which add to 666, and was used to secretly speak against the emperor.>>

[TheZuke!]

Thanks Neufer,
I can always count on you
to shoot me out of the saddle!
B^)

[TheZuke!]

Well, seven "planets" in the night sky - the Sun, ...

Ann

Seeing the Sun in the night sky, my oh my.

You just need to know where to look for it.
It is tougher to see when it is turned off.