Byork wrote:
I wonder if APOD could supply image and data for the star Mizar including where to look for it in the sky (I want to test my eye sight).
Byork, do you live relatively far north of the equator? Because if you do, that means that you can probably see Mizar every clear night. You need to look north, where you will find the Big Dipper.
Take a look at the drawing of the Big Dipper that I have posted here. You can't be sure of the orientation of the Big Dipper - it may be positioned like it is in this picture, or it may be sideways or even upside down. But the general shape of the Big Dipper is easy to recognize.
When you have found the Big Dipper, you need to concentrate of the handle of it, not the bowl. Mizar is the second star in the handle, if you start from the outermost part of it. You can see in the image I posted that Mizar and Alcor are shown as a pink and blue double star. Don't expect them to look anything but white, however.
What interests me most with today's APOD is the Leo I dwarf - is this object a galaxy or a star cluster ?
Leo 1 is definitely a galaxy, not a cluster. Two things show that it is a galaxy. First, Leo 1 is simply too massive to be a cluster, since its mass is estimated to be 10-30
million times the mass of the Sun. Star clusters don't come that massive.
Second, and even more important, Leo 1 is a multi-generation conglomerate of stars. If you follow one of the links for today's APOD, you'll come to a wikipedia page about Leo 1 where you can read the following:
Gallart et al. (1999) deduce from Hubble Space Telescope observations that the galaxy experienced a major increase (accounting for 70% to 80% of its population) in its star formation rate between 6 Ga and 2 Ga (billion years ago). There is no significant evidence of any stars that are more than 10 Ga old. About 1 Ga ago, star formation in Leo I appears to have dropped suddenly to an almost negligible rate. Some low-level activity may have continued until 200-500 Ma.
So Leo 1 was continuously forming stars for at least four billion years. No star cluster can do that. A star cluster is basically a single-generation conglomerate of stars, where all the members were born at more or less the same time out of the same gas cloud. It is possible for members of the same star cluster to have ages that differ by a few million years, but never, ever a billion years. The reason is that a cluster is always born out of the same gas cloud, as I said, and it may take a few million years for this gas cloud to turn itself into a cluster of stars. But after even a few dozen million years all the gas will be gone from the cluster, and no new stars can be born here. A galaxy, even a dwarf galaxy, has or had access to a much larger and more widespread and clumpy supply of gas. It uses or used up this gas supply gradually, over a long period of time, or in sudden, separate bursts.
And, would it possible to resolve individual stars of this object.
Yes, that would certainly be possible. There are no ultra-bright stars in Leo 1, but there are certainly red giants which are intrinsically brighter than Regulus. With a good telescope or with good photography techniques, it would certainly be possible to photograph some of these red giants individually.
How would individual stars of this object fare with regard to existence of habitable planets ?
According to our current understanding, Leo 1 is probably not an extremely promising place to look for habitable planets. Wikipedia wrote this about Leo 1:
Typical to a dwarf galaxy, the metallicity of Leo I is very low, only one percent that of the Sun.
"Metals" in astro-speak mean any elements that are heavier than hydrogen and helium. Without a reasonably good supply of oxygen, carbon, silicon, iron and other elements that make up most of the Earth, it is hard to make rocky planets. Presumably most of the planets in Leo 1 are gas giants rather than rocky planets like the Earth, although admittedly we don't know enough to be quite sure of that.
There is very good reason to believe that Leo I dwarf is brighter than it actually appears; the cluster seems to be enshrouded in a globule of gas. The Leo I dwarf may be comparable to the Pleiades cluster in many ways.
I think you are both right and wrong about that. Wikipedia wrote this about Leo 1:
In addition, the galaxy may be embedded in a cloud of ionized gas with a mass similar to that of the whole galaxy.
But the Pleiades are embedded in a dust cloud, which spreads the blue light of the brightest stars and creates the beautiful nebula. We see no sign that the the ionized gas around Leo 1 is spreading the light of the constituent stars in a reflection nebula that is at all similar to the Pleiades nebula.
The reason why Leo 1 looks so faint is twofold. First, it is really far away, 800,000 light-years compared with 75 light-years for Regulus. So Leo 1 is at lest 10,000 times farther away than Regulus! No wonder it looks faint. The other reason why Leo 1 looks faint is that its stars are spread out over a relatively large volume. That means that the "stellar density" inside the galaxy is low. The stars are simply quite far apart. And there is no part of the galaxy where the stellar density is high.
But it is fascinating to think that if Regulus was sitting inside this dwarf galaxy, it wouldn't be its brightest star, although its blue color in combination with its brightness would indeed make it stand out.
Ann
Bright Star Regulus near the Leo I Dwarf Galaxy
