Starship Asterisk*

Sandstone wrote:A cosmic rose for Valentine's Day... how appropriate!

BillLee wrote:Warning: Newbie alert!

I am NOT an astonomer or anything! But I enjoy the fantastic images in the APOD. I have gathered a large number of them and use them for my screen background.

Question: How do you distinguish stars referenced in an image like the one today (Rosette Nebula) from foreground stars?

I.e.: the description says "...winds and radiation from its central cluster of hot young stars...". How can I tell which of the many stars in the central area of the image are those referenced and not some star in the foreground?

Thanks.

Regards,

Bill Lee

BillLee wrote:Question: How do you distinguish stars referenced in an image like the one today (Rosette Nebula) from foreground stars?

http://en.wikipedia.org/wiki/Garden_roses wrote:

Click to play embedded YouTube video.

[b][color=#0000FF]18th century painting of the China Rose (月季)[/color][/b]

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<<It is believed that roses were grown in all the early civilisations of temperate latitudes from at least 5000 years ago. They are known to have been grown in ancient Babylon. Paintings of roses have been discovered in Egyptian pyramid tombs from the 14th century BC. Records exist of them being grown in Chinese gardens and Greek gardens from at least 500 BC. Most of the plants grown in these early gardens are likely to have been either species collected from the wild, or selections from them.

The significant breeding of modern times started slowly in Europe, from about the seventeenth century. This was encouraged by the introduction of new species, and especially by the introduction of the China rose in the nineteenth century. An enormous range of roses has been bred since then. A major contributor in the early 19th century was Empress Josephine of France who patronized the development of rose breeding at her gardens at Malmaison. As long ago as 1840 a collection numbering over one thousand different cultivars, varieties and species was possible when a rosarium was planted by Loddiges nursery for Abney Park Cemetery, an early Victorian garden cemetery and arboretum in England.

Rose perfumes are made from attar of roses or rose oil, which is a mixture of volatile essential oils obtained by steam distilling the crushed petals of roses. An associated product is rose water which is used for cooking, cosmetics, medicine and in religious practices. The production technique originated in Persia then spread through Arabia and India, and more recently into eastern Europe. In Bulgaria, Iran and Germany, damask roses (Rosa damascena 'Trigintipetala') are used. In other parts of the world Rosa centifolia is commonly used. The oil is transparent pale yellow or yellow-grey in colour. 'Rose Absolute' is solvent-extracted with hexane and produces a darker oil, dark yellow to orange in colour. The weight of oil extracted is about one three-thousandth to one six-thousandth of the weight of the flowers; for example, about two thousand flowers are required to produce one gram of oil.

The main constituents of attar of roses are the fragrant alcohols geraniol and l-citronellol; and rose camphor, an odourless paraffin. β-Damascenone is also a significant contributor to the scent. Rose water, made as a byproduct of rose oil production, is widely used in Asian and Middle Eastern cuisine. In France there is much use of rose syrup, most commonly made from an extract of rose petals. In the United States, this French rose syrup is used to make rose scones and marshmallows.>>

Beyond wrote:
Marshmallows I don't remember any marshmallows ever tasting or smelling anything like roses.

http://en.wikipedia.org/wiki/Marshmallow wrote:

<<The marshmallow probably first came into being as a medicinal substance, since the mucilaginous extracts comes from the root of the marshmallow plant, Althaea officinalis, which were used as a remedy for sore throats.

Concoctions of other parts of the marshmallow plant had medical uses as well. The root has been used since Egyptian antiquity in a honey-sweetened confection useful in the treatment of sore throat. The later French version of the recipe, called pâte de guimauve, included an egg white meringue and was often flavored with rose water. Pâte de guimauve more closely resembles contemporary commercially available marshmallows, which no longer contain any marshmallow plant.

The use of marshmallow to make a candy dates back to ancient Egypt, where the recipe called for extracting sap from the plant and mixing it with nuts and honey. Another pre-modern recipe uses the pith of the marshmallow plant, rather than the sap. The stem was peeled back to reveal the soft and spongy pith, which was boiled in sugar syrup and dried to produce a soft, chewy confection. Candymakers in early 19th century France made the innovation of whipping up the marshmallow sap and sweetening it, to make a confection similar to modern marshmallow. The confection was made locally, however, by the owners of small candy stores. They would extract the sap from the mallow plant's root, and whip it themselves. The candy was very popular, but its manufacture was labor-intensive. In the late 19th century, French manufacturers devised a way to get around this by using egg whites or gelatin, combined with modified corn starch, to create the chewy base. This avoided the laborious extraction process, but it did require industrial methods to combine the gelatin and corn starch in the right way. Also related are the German confectionery called Schaumkuss.

Another milestone in the development of the modern marshmallow was the extrusion process by the American Alex Doumak in 1948. This invention allowed marshmallows to be manufactured in a fully automated way. The method produced the cylindrical shape that are now associated with marshmallows. The process involves running the ingredients through tubes and then extruding the finished product as a soft cylinder, which is then cut into sections and rolled in a mixture of finely powdered cornstarch and confectioner's sugar. Doumak founded the Doumak company in 1961 on the strength of his patent on this process.

Marshmallows, like most candies, are sweetened with sucrose. They are currently prepared by aeration of mixtures of sucrose and proteins to a final density of about 0.5 g/mL. The viscosity of the mixture, owing to the proteins, gelatin or egg albumin, prevents collapse of the air-filled cells. Marshmallows are popular in Asia, particularly in the previous colonies of the UK. One of the largest suppliers in Asia is Erko Foods, based in China. The company exports to 56 countries. Erko is also the market leader in the Middle East, where their Halal marshmallow is sold.>>

Chris Peterson wrote:

BillLee wrote:Question: How do you distinguish stars referenced in an image like the one today (Rosette Nebula) from foreground stars?

Mostly, you can't just by looking at an image like this. In an image of another galaxy, virtually every star in the image is a foreground object. But when looking at nearby objects like this nebula, there may be more background stars than foreground ones, and without additional information from other instruments, there is usually no way to tell for sure which are which.

However, when you have an emission nebula like this, something energetic needs to be driving it, and that is often a small cluster of hot, bright stars. The fact that you can see just that in this image- at the center of the nebula (blue tells us they are hot, the diffraction spikes mark them as relatively bright and probably close), with a zone around them free of dust and gas- should provide a strong hint that these stars are inside the nebula. And indeed, they are. Other bright stars (those with diffraction spikes) are probably foreground stars, but not necessarily. The majority of dimmer stars are probably in the background, but again, not necessarily.

Ann wrote:The blue stars in the middle of the nebula have typical parallaxes of about 0.5 milliarcseconds, which is very little and marks them as far away.

Chris Peterson wrote:

Ann wrote:
The blue stars in the middle of the nebula have typical parallaxes of about 0.5 milliarcseconds, which is very little and marks them as far away.

I'd argue that any star with a detectable parallax is, in fact, very near!
Such an elegant method... it's a shame we can only use it for the tiniest fraction of objects we are able to observe.

http://en.wikipedia.org/wiki/Hipparcos wrote:
<<Hipparcos (an acronym for "High precision parallax collecting satellite") was a scientific mission of the European Space Agency (ESA), launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky. This permits the accurate determination of proper motions and parallaxes of stars, allowing a determination of their distance and tangential velocity. When combined with radial velocity measurements from spectroscopy, this fixes all six quantities needed to determine the motion of the star. The Hipparcos Catalogue, a high-precision catalogue of more than 100,000 stars, was published in 1997. Observationally, the objective was to provide the positions, parallaxes, and annual proper motions for some 100,000 stars with an unprecedented accuracy of 2 milliarcseconds, a target in practice eventually surpassed by a factor of two. >>

http://iopscience.iop.org/0004-637X/571/2/906/fulltext/ wrote:
The Astrophysical Journal, 571:906-917, 2002 June 1
© 2002. The American Astronomical Society. All rights reserved. Printed in U.S.A.
Very Long Baseline Array Measurement of Nine Pulsar Parallaxes
Walter F. Brisken , John M. Benson , and W. M. Goss and S. E. Thorsett

ABSTRACT: <<We determined the distances to nine pulsars by parallax measurements using the NRAO Very Long Baseline Array, doubling the number of pulsars with accurate distance measurements. Broadband phase modeling was used to calibrate the varying dispersive effects of the ionosphere and remove the resulting phase errors from the phase-referenced VLBI data. The resulting parallaxes have a typical accuracy of [0.1 milliarcseconds] or better, yielding distance measurements as accurate as 2%. We also report new proper motion measurements of these pulsars, accurate to [0.4 milliarcseconds] yr-1 or better.>>

http://en.wikipedia.org/wiki/Gaia_%28spacecraft%29 wrote:
<<Gaia (or Global Astrometric Interferometer for Astrophysics) is a European Space Agency (ESA) space mission in astrometry and a successor to ESA's Hipparcos mission. It is part of the ESA Horizon 2000 Plus long-term scientific program and expected to launch in March 2013. Gaia will compile a catalogue of approximately 1 billion stars in our galaxy to magnitude 20. Its objectives comprise:

• astrometric (or positional) measurements, determining the positions, distances, and annual proper motions of stars with an accuracy of about 0.02 milliarcseconds at 15 mag, and 0.2 milliarcseconds at 20 mag
  
  spectrophotometric measurements, providing multi-epoch observations of each detected object
  
  radial velocity measurements.

Gaia will create an extremely precise three-dimensional map of stars throughout our Milky Way galaxy and beyond, and map their motions which encode the origin and subsequent evolution of the Milky Way. The spectrophotometric measurements will provide the detailed physical properties of each star observed, characterising their luminosity, effective temperature, gravity and elemental composition. This massive stellar census will provide the basic observational data to tackle a wide range of important problems related to the origin, structure, and evolutionary history of our Galaxy. Large numbers of quasars, galaxies, extrasolar planets and solar system bodies will be measured at the same time.

Gaia will also be capable of discovering asteroids with orbits that lie between Earth and the Sun, a region that is difficult for Earth-based telescopes to monitor since this region is only in the sky during or near the daytime.

Gaia will be launched on a Soyuz-FG rocket in August 2013 and will fly to the Lagrange point L2 located approximately 1.5 million kilometers from Earth. The L2 point will provide the spacecraft with a very stable thermal environment. There it will describe a Lissajous orbit which will avoid eclipses of the Sun by the Earth, which would otherwise limit the amount of solar energy the satellite can retrieve through its solar panels and also disturb the thermal equilibrium.

Similarly to its predecessor Hipparcos, Gaia consists of two telescopes providing two observing directions with a fixed, wide angle between them. The spacecraft rotates continuously around an axis perpendicular to the two telescopes' lines of sight (LOS). The spin axis in turn has a slight precession across the sky, while maintaining the same angle to the Sun. By precisely measuring the relative positions of objects from both observing directions, a rigid system of reference is obtained.

Despite its name, Gaia does not actually use interferometry to determine the positions of stars. At the time of the original design, interferometry seemed the best way to achieve the target resolution, but the design later evolved into an imaging telescope.

Each celestial object will be observed on average about 70 times during the mission, which is expected to last 5 years. These measurements will help determine the astrometric parameters of stars: 2 corresponding to the angular position of a given star on the sky, 2 for the derivatives of the star's position over time (motion) and lastly, the star's parallax. The radial velocity of the star is measured using the Doppler Effect by a spectrometer, which is integrated into the Gaia telescope system.>>

http://en.wikipedia.org/wiki/Spektr-R wrote:
<<Spektr-R[2] (or Radioastron) is a Russian orbital radio telescope, and currently the largest space telescope in orbit.. It is funded by the Russian Astro Space Center, and was launched into Earth orbit on 18 July 2011,.\ with a perigee of 10,000 kilometers (6,200 mi) and an apogee of 390,000 kilometers (240,000 mi), about 700 times the orbital height of the Hubble Space Telescope.. The main scientific goal of the mission is the study of astronomical objects with an angular resolution up to a few millionths of an arcsecond. This is accomplished by using the satellite in conjunction with ground-based observatories and interferometry techniques.>>

neufer wrote:Such an elegant method... with improved technology there is almost no limit in the number of galactic objects we will be able to observe in the future