Term
|
Definition
| is a huge collection of stellar and interstellar matter isolated in space and bound together by its own gravity. |
|
|
Term
|
Definition
| Flattened region of gas and dust that bisedts the galactic halo in a spiral galaxy. This is the region of active star formation. |
|
|
Term
|
Definition
| Thick distribution of warm gas and stars around the galactic center. |
|
|
Term
|
Definition
| Region of a galaxy extending far above and below the galactic disk, where globular clusters and other old stars reside. |
|
|
Term
|
Definition
| Galaxy composed of a flattened, star forming disk component which may have spiral arms and a large central galactic bulge. |
|
|
Term
|
Definition
| A star whose luminosity changes with time. |
|
|
Term
| PULSATING VARIABLE STARS 621 |
|
Definition
| A star whose luminosity varies in a predictable, periodic way. |
|
|
Term
|
Definition
| variable star whose luminosity changes in a characteristic way. All rr lyrae stars have more or less the same average luminosity. |
|
|
Term
|
Definition
| Star whose luminosity varies in a characteristic way, with a rapid rise in brightness followed by a slower decline. The period of a Cepheid variable star is related to its luminosity, so a determination of this period can be used to obtain an estimate of the stars distance. |
|
|
Term
| COSMIC DISTANCE SCALE 622 |
|
Definition
| apparent brightness = luminosity / (distance)squared |
|
|
Term
| period-luminosity relationship 623 |
|
Definition
| A relation between the pulsation period of a cepheid variable and its absolute brightness. Measurement of the puslation periood allows the distance of the star to be determined. |
|
|
Term
|
Definition
| The center of the Milky Way, or any other galaxy. The point about which the disk of a spiral galaxy rotates. |
|
|
Term
|
Definition
| distribution of material in a galaxy forming a pin wheel shaped design, beginning near the galactic center. |
|
|
Term
|
Definition
(1) a wave of matter formed in the plane of planetary rings, similar to ripples on the surface of a pond, which wrap around the rings forming spiral patterns similar to grooves in a record dissk. Spiral density waves can lead to the appearance of ringlets.
(2) proposed explanation for the existence of galactic spiral arms, in which coiled waves of gas compression move thru the galactic dissk, triggering star formation. |
|
|
Term
| SELF PROPAGATING STAR FORMATION 634 |
|
Definition
| Mode of star formation in which shock waves produced by the formation and evolution of one generation of stars triggers the formation of the next. |
|
|
Term
| MASS OF 2 OBJECTS/LAW OF GRAVITY/KEPLERS 3RD LAW P 636 |
|
Definition
total mass (solar masses) =
orbal size (AU) 3rd/
orbital period (years) 2nd |
|
|
Term
|
Definition
| Plot of the orbital speed of disk material in a galaxy against its distance fom the galactic center. Analysis of rotation curves of spiral galaxies indicates the existence of dark matter. |
|
|
Term
|
Definition
| Region of a galaxy beyond the visible halo where dark matter is believed to reside. |
|
|
Term
|
Definition
| Term used to describle the mass in galaxies and clusters whose ezistence we infer from rotation curves and other techniques, but that has not been confirmed by observations at any electromagnetic wavelength. |
|
|
Term
| GRAVITATIONAL LENSING 639 |
|
Definition
| The effect induced on the image of a distant object by a massive foreground object. Light from the distant object is bent into two or more separate images. |
|
|
