The Astrophysics Spectator

Issue 2.35, November 2, 2005

Home Commentary Surveys Research Background Store Previously Site Info
Logo for The Astrophysics Spectator.

The basic layout of the site is as survey paths, which can be found under the Surveys link at the top of this and most other pages on this site. Each survey begins with a basic overview of the subject. Part of this overview include simulators of astrophysical phenomena that allow the reader to experiment with the phenomena. The later pages in a survey present the subject in greater and more mathematical depth. A path ends with research pages that describe current research projects and results in astrophysics.

The links at the top of each page are Home, which is the current home page of this site, Commentary, which is an index of short essays on topics loosely related to astrophysics, Surveys, which is the index of survey paths, Research, which is the index of research pages and the page leading to recent news items, Background, which is the index page for all background information on astrophysics, including survey pages, simulator pages, tables, bibliographic references, and lists of web resources, Previously, which is an index of previous home pages, and Site Info, which describes the site and its author, and gives contact information.

On the home page is found an addition link. This is the Store link, which leads to reviews of worthwhile books on astronomy and other relates subjects. Links on these pages enable the reader to buy these books from, which helps to financially sustain this web site.

On Wednesday of every fortnight, a new issue of The Astrophysics Spectator is published that comprises a new home page, a new commentary, whatever news the author notices, and background, research, and simulator pages added to the survey paths. The home page acts as an index to the newly added pages. This site also has an RSS channel, whose link is given at the bottom of the right-hand column of this page.

November 2, 2005

The pages added in the previous issue of The Astrophysics Spectator describe how light travels on a curved path as it passes a star or planet. This effect gives to each star and planet a gravitational lens. If the lens is far enough away from us, we will see the objects beyond the lens distorted either into rings that encircles the lens source or into pairs of elongated images flanking the lens source. This issue of The Astrophysics Spectator adds a new simulator to the “General Relativity” survey path that illustrates this behavior.

We are too close to the Sun to see much of an effect of its gravitational lens on the objects behind it. For us to see the Sun's gravitational lens dramatically distort the distant stars, we would have to be several hundred time more distant from the Sun than we are on Earth. The other stars in our Galaxy, however, are more than sufficiently distant for their lenses to distort the images of more distant objects. With so many stars in the Galaxy, the chances are good for seeing the effects of a star's lens on more distant stars.

The most interesting effect, the distortion of the image of a distant object by a star's lens, cannot be seen with our telescopes— the distortions in shape are too small in angle. What we can see, however, is the increase in intensity of an object as a gravitational lens passes in front. This effect occurs because a gravitational lens causes the image of an object to cover a larger area on the sky without altering its surface brightness. The luminosity of the object increases proportionally with the increase of the image's area on the sky.

The simulator added this week shows the image created by a point gravitational lens. Depending on where the lens is placed relative to a more distant object, the image can be double, or it can be a ring, called an Einstein ring, that completely encompasses the lens source. The reader can moving the lens source in the simulator to obtain either effect.

Publication Notice. The next issue of The Astrophysics Spectator is slated for November 16.


A Star's Gravitational Lens. This simulator shows the image produced by the gravitational lens created by a distant star. The reader can move the lens relative to the object behind the lens to produce either an Einstein ring or a pair of images of the source. (continue)


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