APOD: M45: The Pleiades Star Cluster (2016 Oct 19)

[APOD Robot]

M45: The Pleiades Star Cluster

Explanation: Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as dusty as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars even from the heart of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured image was a long duration exposure taken last month from Namibia and covers a sky area many times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of visible Pleiades stars, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

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[Ann]

Nice image! I'm always happy to see an RGB image of the Pleiades!

What I think is particularly good about today's APOD is that it highlights the brown gunky dust that permeates the field, and which is just lit up in blue as the Pleiades Cluster is passing by.

Thanks to the editors for posting the APOD Retrospective of the Pleiades Cluster! There are many great images there.

And don't miss the Recent Submissions thread here at Starship Asterisk*! There are many fine Pleiades pictures here, and Hermann von Eiff's image is one of them.

Ann

[Boomer12k]

A very ethereal scene....with awesome detail.

We have a clear sky with the Moon out, but it is cold and damp after the week of stormy weather.
:---[===] *

[Asterhole]

Right up there with the Orion Nebula, this is an iconic telescopic destination - and nicely presented here as well!

[zzwerzy]

Forgive my noob question, but may I ask: do we know how many stars are in M45?

[neufer]

... do we know how many stars are in M45?

<<The Pleiades (Messier 45 or M45) is an open star cluster containing middle-aged, hot B-type stars located in the constellation of Taurus. The cluster core radius is about 8 light years and tidal radius is about 43 light years. The cluster contains over 1,000 statistically confirmed members, although this figure excludes unresolved binary stars. It is dominated by young, hot blue stars, up to 14 of which can be seen with the naked eye depending on local observing conditions. The total mass contained in the cluster is estimated to be about 800 solar masses.

The cluster contains many brown dwarfs, which are objects with less than about 8% of the Sun's mass, not heavy enough for nuclear fusion reactions to start in their cores and become proper stars. They may constitute up to 25% of the total population of the cluster, although they contribute less than 2% of the total mass. Astronomers have made great efforts to find and analyse brown dwarfs in the Pleiades and other young clusters, because they are still relatively bright and observable, while brown dwarfs in older clusters have faded and are much more difficult to study.>>

[ta152h0]

might get to see them tonight, along with Orion and its souther neighbor Sirius

[ta152h0]

Saw the daytie Moon this morning

[Fred the Cat]

The Pleiades have made a good ad gimmick but I think today's image is angelic.

[BillT]

The distance to the cluster is (maybe was) a small controversy. Radio telescope VLBI and a number of other methods measured the distance at around 135 parsecs, whereas the ESA Hipparcos satellite gave a result around 118 parsecs, well outside the margin of error. The first data release from the ESA Gaia satellite gives a preliminary result of 134 ±6 pc. The Gaia specialists say they are cautious about the result at this stage but it seems to confirm the suggestion of some kind of systematic error in the Hipparcos result.

[Ann]

The distance to the cluster is (maybe was) a small controversy. Radio telescope VLBI and a number of other methods measured the distance at around 135 parsecs, whereas the ESA Hipparcos satellite gave a result around 118 parsecs, well outside the margin of error. The first data release from the ESA Gaia satellite gives a preliminary result of 134 ±6 pc. The Gaia specialists say they are cautious about the result at this stage but it seems to confirm the suggestion of some kind of systematic error in the Hipparcos result.

That's very interesting.

And that's why I'm sorry that Gaia won't measure the distance to stars brighter than sixth magnitude, if I have understood things correctly.

If Hipparcos underestimated the distance to the Pleiades, who knows what other stellar distances it may have underestimated or overestimated?

Ann

[Chris Peterson]

And that's why I'm sorry that Gaia won't measure the distance to stars brighter than sixth magnitude, if I have understood things correctly.

I predict that once the primary mission goals are achieved, they'll figure out clever ways to look at things which the instruments weren't strictly designed for. That seems to be the general pattern with such missions.

If Hipparcos underestimated the distance to the Pleiades, who knows what other stellar distances it may have underestimated or overestimated?

I believe that one of the expectations of the Gaia data is that it will allow the nature of Hipparcos's systematic error problem to be determined, or better determined. That may be academic, depending on how much of the Hipparcos data is replaced by Gaia data.