Astronomy 162
Introduction to Stellar, Galactic & Extragalactic Astronomy

Digital Movie Gallery

These digital movies illustrate some of the concepts discussed in Astronomy 162. With slight modification, they are identical to the movies being shown in lecture. Since these movies are experimental, your feedback would be greatly appreciated.

Most of the movies are available in one or more of the following three formats: QuickTime, MPEG, and animated GIF. QT viewers are readily available as plug-in options for common PC and Mac browsers (e.g., Netscape and Internet Explorer). MPEG is the de facto standard in the Unix world (although Unix users should note that the latest versions of "xanim" support QT movies). Animated GIFs may be viewed using most browsers, and with the xanim tool on Unix boxes. In most cases, the animated GIF versions are reduced in size and length to facilitate easy downloads for slow connections.

Copyright Notice

All data files are Copyright Richard W. Pogge, All Rights Reserved. Please read the Copyright Notice for specific copying and use rights.


Trigonometric Parallax

1.3Mb QuickTime Movie
86Kb MPEG Movie
224Kb Animated GIF
Still (3Kb GIF)

This movie demonstrates Trigonometic Parallax. The top half of each frame shows the appearance of the sky as seen from the Earth (ignoring the Sun), and the bottom half shows a fixed view looking down from above onto the plane of the Earth's orbit around the Sun (the ecliptic). A red star is shown located some distance to the right (also in the ecliptic plane). In this simulation, the star is fixed in space with respect to the Sun, and its proximity to the Sun is greatly exaggerated to help make its parallax easy to see.

In the first half of the movie, the parallax motion of the red star over the course of one year is shown. Note that the star is not moving through space, as can be seen in the bottom panel, only the Earth is moving. The star's parallax motion is simply a reflection of the Earth's orbital motion. When viewed from the moving Earth (top panel), the red star appears to move first west (towards the right) then east (towards the left) with respect to the distant background stars which are so far away that their parallax motions are too small to be seen at this scale.

In the second half, we move the star 2x farther away (as indicated by the scale bar at the bottom) and run through another year. Now the annual the trigonometric parallax motions are 2x smaller because the distance to the star is 2x greater. This fact, that the trigonometric parallax of a star is inversely proportional to its distance from the Sun gives us a direct measurement of the star's distance.

Note that the parallax motion of the star is an illusion due to the orbital motion of the Earth around the Sun. Real stars are much more distant than shown here. For example, one of the nearest stars, Alpha Centauri, is about 277,000 AU away, resulting in a parallax of about 0.74 arcseconds.

[Credit: R. Pogge, OSU]

Proper Motion of Ursa Major (the Big Dipper)

2.3Mb QuickTime Movie
480Kb MPEG Movie
136Kb Animated GIF
Still (3Kb GIF)

This movie shows the appearance of the Big Dipper (Ursa Major) for a 200,000 year period between 100,000 BC and 100,000 AD demonstrating the proper motion of the stars. All stars down to 6.5 magnitude are shown, and the timestep is 1000 years. Most of the bright stars making up the familiar constellation of the Big Dipper are part of a moving group, and can clearly be seen to be moving together towards the East (left on the frame) over time. Watch for very fast moving stars that cross the field over the 200,000 year period of this animation.

[Credit: R. Pogge, OSU]

Visual Binary Stars

Circular Orbit:
520Kb QuickTime Movie
60Kb MPEG Movie
216Kb Animated GIF
Still (5Kb GIF)

Elliptical Orbit (e=0.4):
512Kb QuickTime Movie
58Kb MPEG Movie
208Kb Animated GIF
Still (5Kb GIF)

These movies simulate the orbit of a visual binary star pair consisting of an F0v primary and M0v secondary. The orbital plane of the two is in the plane of the sky. The two stars have a mass ratio of about 3.6, appropriate for stars of this type.

The first movie shows the two stars in circular orbits about their center of mass (marked with the green dot). Two orbits are shown, with the orbit traced as a white line. Both stars move at a uniform speed around the center of mass, the more massive, blueish F0v star moves less as it is closer to the center-of-mass than the less massive, reddish M0v star.

The second movie shows the two stars in elliptical orbits about their center of mass, with an orbital eccentricity of 0.4. Watch how both stars noticeably speed up and slow down as they pass periastron (closest approach to the C-of-M) and apastron (farthest from C-of-M), respectively, thus obeying Kepler's Second Law (equal areas in equal times) the same as the planets in the Solar System.

[Credit: R. Pogge, OSU]

Spectroscopic Binary Star

970Kb QuickTime Movie
67Kb MPEG Movie
401Kb Animated GIF
Still (7Kb GIF)

This movie simulates a double-lined spectroscopic binary star system consisting of an F0v primary and M0v secondary in a circular orbit about each other. The orbital plane is oriented along the line of sight in this simulation. The top half of the frame shows the appearance of the two stars seen from above, with the red dot marking the center of mass of the system, and the green dot at left indicating the location of the distant observer. The bottom half of the frame shows the spectrum seen by the distant observer. The absorption lines from the primary star are labeled "A", while those from the secondary star are labeled "B". As the two stars orbit each other, they alternately move towards then away from the observer. This results in their absorption-line spectra getting blue-shifted, then red-shifted, respectively. The pattern of Doppler shifts traces out the orbital motions of each star. A thin "stationary" absorption line appearing between the two lines shows the un-shifted location of each line.

Notice that the primary star's absorption lines (labeled "A") only shift a small amount, reflecting its smaller orbital velocity, compared to that of the secondary, which moves much faster. This because the lower mass secondary star must be located farther from the center-of-mass of the system than the primary, and so has to trace out a much bigger circle in its orbit in the same time that the primary does, making its Doppler shift larger in proportion to their mass ratio.

The amount of Doppler shift seen in this simulation has been greatly exaggerated to make it easily visible.

[Credit: R. Pogge, OSU]

Eclipsing Binary Star

728Kb QuickTime Movie
53Kb MPEG Movie
288Kb Animated GIF
Still (6Kb GIF)

This movie simulates an eclipsing binary star system consisting of an A0v primary and G5v secondary in a circular orbit about each other. The orbital plane is tilted with respect to the line of sight by 6°. The top half of the frame shows the appearance of the two stars, with the red dot marking the center of mass of the system (just outside the radius of the blueish A0v primary star). The light curve of the total system is traced out in the lower panel as they orbit. Two orbits full orbits are shown, with a red marker used on the light curve to show the current location.

Notice that the deepest eclipse occurs when the secondary is in front of the primary. This is because of the nearly factor of two greater effective temperature of the primary (10,000K compared to 5,500K). Since surface brightness scales like T4, more light is blocked when the secondary is blocking part of the primary, than when the primary completely blocks the secondary.

[Credit: R. Pogge, OSU]

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Updated: 2007 November 3 [rwp]

Copyright Richard W. Pogge, All Rights Reserved.