APOD: Mars and the Pleiades Beyond Vinegar... (2021 Apr 06)

[APOD Robot]

Mars and the Pleiades Beyond Vinegar Hill

Explanation: Is this just a lonely tree on an empty hill? To start, perhaps, but look beyond. There, a busy universe may wait to be discovered. First, physically, to the left of the tree, is the planet Mars. The red planet, which is the new home to NASA's Perseverance rover, remains visible this month at sunset above the western horizon. To the tree's right is the Pleiades, a bright cluster of stars dominated by several bright blue stars. The featured picture is a composite of several separate foreground and background images taken within a few hours of each other, early last month, from the same location on Vinegar Hill in Milford, Nova Scotia, Canada. At that time, <a rhef="ap210304.html">Mars was passing</a> slowly, night after night, nearly in front of the distant Seven Sisters star cluster. The next time Mars will pass angularly as close to the Pleiades as it did in March will be in 2038.

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[Ann]

That's a lovely photo!

And please don't complain about that fact that it is a composite, because it says so in the caption.

Ann

[Knight of Clear Skies]

Something I've wondered about, what is the true extent of the Pleiades please? As I understand it we can easily pick out the dense core but it extends much further than this. I'd have thought data from Gaia could answer this question, I found this paper online but don't understand the scale on the diagram (pc = parsecs?). Would be interesting to know how this relates to an angular size.

Click to view full size image

For example, the field of view in this image taken on 6th March is 12x10 degrees. Am I right in thinking there are cluster members hiding all over the frame?

[Ann]

Something I've wondered about, what is the true extent of the Pleiades please? As I understand it we can easily pick out the dense core but it extends much further than this. I'd have thought data from Gaia could answer this question, I found this paper online but don't understand the scale on the diagram (pc = parsecs?). Would be interesting to know how this relates to an angular size.

Click to view full size image

For example, the field of view in this image taken on 6th March is 12x10 degrees. Am I right in thinking there are cluster members hiding all over the frame?

Click to play embedded YouTube video.

I can't tell you about the Pleiades, but I just found a fascinating video about the Hyades. The Hyades appears to have two huge tidal tails, which together cover a thousand light-years.

The Hyades appears to have been disrupted by something very massive a few hundred million years ago, possibly a chunk of dark matter.

Ann

[Knight of Clear Skies]

Thanks Ann. Shows that Gaia can go beyond identifying cluster members but can pick out probably past members too and find past interactions.

[Knight of Clear Skies]

Digging into the paper I linked to, Pleiades cluster members were found stretching over about 110 light years. This gives an angular size of over 14 degrees, assuming I'm understanding correctly.

"We calculated the tidal radius as in Sect. 4.1, deriving 11.6 pc, with a total of 1248 sources. The number of sources within the core and half-mass (4.5 pc) radii are 106 and 495, respectively. We limited our search for member candidates up to three times the tidal radius (i.e. 34.8 pc)."

[E Fish]

Beautiful. That's my favorite star cluster (and I love seeing it as Ann's avatar, too ).

[neufer]

Digging into the paper I linked to, Pleiades cluster members were found stretching over about 110 light years. This gives an angular size of over 14 degrees, assuming I'm understanding correctly.

"We calculated the tidal radius as in Sect. 4.1, deriving 11.6 pc, with a total of 1248 sources. The number of sources within the core and half-mass (4.5 pc) radii are 106 and 495, respectively. We limited our search for member candidates up to three times the tidal radius (i.e. 34.8 pc)."

Note: The tidal radius (i.e., Hill sphere) of the Earth is 231 times the actual radius of the Earth.

<<Tidal radius, or Hill sphere, is the distance from the center of the globular cluster at which the external gravitation of the galaxy has more influence over the stars in the cluster than does the cluster itself. This is the distance at which the individual stars belonging to a cluster can be separated away by the galaxy.

M45 The Pleiades / Moon Occulation

The Pleiades cluster core radius is about 8 light-years [~1º] and tidal radius is about 43 light-years [~5.5º]. The cluster contains over 1,000 statistically confirmed members, a figure that excludes an unresolved likely further number of binary stars. Its light is dominated by young, hot blue stars, up to 14 of which can be seen with the naked eye depending on local observing conditions and visual acuity of the observer.>>

[orin stepanek]

Ahh! Beyond Vinegar Hill; Mars; and beautiful Pleiades! What a
beautiful Photo by Kristine Rose Photography! Today's APOD has
some nice links to Perseverance rover photos! Really gonna make
a nice background wallpaper!

[johnnydeep]

Very nice image. Can we get the Moon and/or another planet or two in the same frame? Is it astronomically possible at a fortuitous time?

[Chris Peterson]

Very nice image. Can we get the Moon and/or another planet or two in the same frame? Is it astronomically possible at a fortuitous time?

The 18.6 year nodal cycle of the Moon is such that there is a window several years long, with that period, where the Moon regularly occults the Pleiades. The last time was in the mid-2000s. The next will start in 2023. So indeed, it would be possible to produce an image like this that included the Moon... although it would be a complex series of images and skilled processing to do so given the immense difference in brightness between the Moon and the nebulosity of the cluster.

[De58te]

Very nice image. Can we get the Moon and/or another planet or two in the same frame? Is it astronomically possible at a fortuitous time?

According to Stellarium, the planet Venus passed right in front of the Pleiades a year ago in the evening of April 3, 2020. Pushing forward the year calendar, Venus will do so again pass in front in 2028, same date April 3. And again in 2036 and again April 4, 2044. The year 2044 is more remarkable that 3 days earlier on April 1, the Moon will be just in front of the Pleiades, with Venus just close by, even closer than Mars to the Pleiades in this picture.

[johnnydeep]

Thanks, Chris and De58te - I can always count on the posters here to flesh out the details!

[neufer]

The first documented evidence of vinegar making and use was by the ancient Babylonians around 3000 BC. They primarily made vinegar from dates, figs, and beer and used it for both culinary and medicinal purposes. The Babylonian star catalogues name the Pleiades ^MULMUL (literally "star star"), and they head the list of stars along the ecliptic, reflecting the fact that they were close to the point of vernal equinox around the 23rd century BC.

[neufer]

Click to play embedded YouTube video.

Mars and the Pleiades Beyond Vinegar Hill

Explanation: Is this just a lonely tree on an empty hill?

Poems are made by fools like me,

But only negative pressure can make a tree.