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Welcome to AstroFly Help




Contents


What Is AstroFly?

AstroFly is a software project, which is intended for educational use; thus, if you are interested in astrophysics, it may help you to expand your knowledge about our Universe. Its main purpose is to present the three-dimensional models of our neighborhood in our own Milky Way Galaxy on a personal computer. The 3D models are based on the remarkable Hipparcos and Tycho Catalogues, which are the products of the European Space Agency's Hipparcos Space Astrometry Mission.

In the first place, we have to clearly state that everything in this project is extremely simplified; therefore, we should rather use the term "3D pseudo-model," not "3D real-model." It is important to perceive all the simplifications of problems in order to understand what these models depict from our Universe. The biggest troubles which we cannot overcome are these:
  • Space-time--in AstroFly, all relativistic effects are ignored; moreover, time itself is also ignored. The trouble is that whenever we look at a star, what we see is not its present state. Actually the state corresponds to the moment at which the light ending on our eye's retina started its journey through the Universe from the star to us. Thus we can look back in time. For example, the star Polaris is about 431 light-years distant; if it eventually exploded as a supernova, we would notice it after 431 years, not sooner, since no information can travel faster than light. In AstroFly, we must assume the infinite speed of light in order to avoid this lack of information caused by the finite speed of light; consequently, the models are distorted. On the other hand, we can fly much faster than light--of course only with this "frozen" time. Furthermore, Einstein's General Theory of Relativity says that space-time is curved or warped by matter and energy in it, so we should compute these effects affecting light: gravitational lensing (a ray of light will be bended on its way to us if it passes through a strong gravitational field) and gravitational redshift (as a photon strives to get out of a gravitational field, it loses energy; and the wavelength of light will be shifted towards redder regions of the spectrum). A much more significant gravitational effect in our case is that stars themselves are moving in space. For instance, stars of our Galaxy are orbiting its center, where a supermassive black hole, a very strong space-time warper, lurks. Nevertheless, none of the above effects are computed in AstroFly because the computational power of a personal computer is not sufficient for these problems.

    To learn more about space-time, black holes, etc. online, visit, for example, these websites:

  • Scale--the size of a point representing a star in AstroFly has nothing to do with the real diameter of the star. To display huge interstellar distances on a small computer screen, we must accept an enormous scale. We can illustrate this by considering a relatively small distance, for example, from our Sun to its nearest star--Proxima Centauri, displayed on a typical computer monitor (17" with 1280 x 1024 resolution). If we assign our Sun to the pixel at the upper left corner and then assign the Proxima Centauri to the pixel at the lower right corner, we will utilize the biggest physically displayable distance on our monitor, its diagonal corresponding to about 40 000 000 000 000 km (1.29 pc, 4.22 ly, or 267 068 AU). In this case the Sun will be depicted by the smallest pixel of the monitor, yet the pixel will correspond to about 24 373 749 103 km in the proportional scale. Thus the diameter of the Sun would be roughly 17 500 times larger than its real value (1 391 980 km) and three times larger than the entire solar system!

  • Temperature--the effective temperature of a star is computed from the Johnson B-V color index; it is assumed that the star is a main sequence member in order to simplify computations. If the star is not a main sequence member, its temperature is slightly different from the value computed by AstroFly. To check this in AstroFly, we can display the star in the Hertzsprung-Russell diagram.
The main sources of information:
  • AstroFly's star databases are based on the Hipparcos and Tycho Catalogues (ESA, 1997). The databases contain fewer records than the original catalogues because AstroFly requires that all the employed parameters of each record must be defined and that the trigonometric parallax parameter of each record must be greater than zero (negative parallaxes are explained in ESA, 1997, vol. 1, pp. 110, 150).
  • Star names are taken from the Hipparcos and Tycho Catalogues (ESA, 1997) and the Bright Star Catalogue (Hoffleit and Warren, 1991).
  • Sun's parameters are taken from Handbook of Space Astronomy and Astrophysics (Zombeck, 1990, p. 25).
Clarification of some abbreviations and acronyms used in AstroFly:
  • DFTS
    distance from the Sun
  • DFYP
    distance from your position
  • FOV
    field-of-view
  • NGP
    north galactic pole (in the 3D model)
  • SGP
    south galactic pole (in the 3D model)
  • T, Q, and D (parameters in the status bar at the bottom of the main window)
    • T
      total number of stars in the selected star database
    • Q
      number of stars that have passed the querying process successfully
    • D
      number of stars that are displayed on the screen

How to Use AstroFly

Moving in Space

You can picture AstroFly as a strange remote-controlled insect that can fly anywhere in space and deliver the view from its position back to you. So that you will be able to control its position and line of sight by using your keyboard and mouse, there are these maneuvers in AstroFly:
  • To change the direction of the line of sight to the left, to the right, up, or down (no change in the position), do one of the following:

    • Hold down the left mouse button + move the mouse to the left, to the right, up, or down respectively.

    • Press Left Arrow, Right Arrow, Up Arrow, or Down Arrow respectively.
  • To rotate the view around the line of sight clockwise or counter-clockwise, do one of the following:

    • Hold down Ctrl + the left mouse button + move the mouse to the left or to the right respectively.

    • Press Ctrl + Left Arrow or Right Arrow respectively.
  • To change the position in a plane perpendicular to the line of sight to the left, to the right, up, or down, do one of the following:

    • Hold down the right mouse button + move the mouse to the left, to the right, up, or down respectively.

    • Press Alt + Left Arrow, Right Arrow, Up Arrow, or Down Arrow respectively.
  • To change the position along the line of sight forward or back, do one of the following:

    • Hold down Ctrl + the right mouse button + move the mouse up or down respectively.

    • Press Ctrl + Alt + Up Arrow or Down Arrow respectively.

    • Use the mouse wheel.
  • To orbit around the center at a specified distance on the line of sight from the position, do one of the following:

    • Hold down the middle mouse button + move the mouse to the left, to the right, up, or down.

    • Hold down Shift + the left mouse button + move the mouse to the left, to the right, up, or down.

    • Press Shift + Left Arrow, Right Arrow, Up Arrow, or Down Arrow.

    The actual radius of orbital motions is specified in the Astro-Fly-Through Control Panel.
  • To return home, do one of the following:

Note: If not specified otherwise, it is assumed that the above commands are available only in the main window, where the 3D model is rendered. In all references to mouse buttons, a right-handed mouse is assumed.

Modifying the Field-of-View Angle

There are several ways to change the field-of-view angle:
  • To decrease or increase the field-of-view angle (zoom in or zoom out) in the main window, do one of the following:

    • Hold down Shift + the right mouse button + move the mouse up or down respectively.

    • Press Plus or Minus respectively.

    • Press Shift + Alt + Up Arrow or Down Arrow respectively.
  • To change the field-of-view angle by using the Main Control Panel, do one of the following:

    • Type the value directly into the FOV Angle in Degrees field.

    • Move the slider of the track bar.

    Both the field and the track bar define the field-of-view angle (in degrees) in the vertical direction.
Filtering Stars

To exclude stars from rendering, use the Filtering Options in the Main Control Panel.
  • To eliminate stars fainter than a specified value of the apparent visual magnitude as seen from the Sun, check the box Limit Visual Magnitude (from the Sun) and specify the value.
  • To eliminate stars that are not located within a specified distance from the Sun, check the box Limit Distance from the Sun in Parsecs and specify the distance in parsecs.
  • To eliminate stars by using other parameters, check the box Use Advanced Options, click the Modify button, and then specify the proper range of each parameter in the Advanced Filtering Options dialog box. A star must meet all of the specified conditions in order to pass the querying process successfully. The default setting is not restrictive. There are these parameters in the dialog box:

    • Hipparcos Catalogue Identifier--HIP (It is available when the Star Database Derived from HIPPARCOS Catalogue option is selected.)

    • Tycho Catalogue Identifier--TYC1 (It is available when the Star Database Derived from TYCHO Catalogue option is selected.)

    • Tycho Catalogue Identifier--TYC2 (It is available when the Star Database Derived from TYCHO Catalogue option is selected. The value 0 represents all objects of the specified TYC1.)

    • Tycho Catalogue Identifier--TYC3 (It is available when the Star Database Derived from TYCHO Catalogue option is selected. The value 0 represents all components of the specified TYC1 and TYC2.)

    • Absolute Visual Magnitude

    • Apparent Visual Magnitude from Your Position

    • Distance from Your Position in Parsecs

    • Trigonometric Parallax in Milliarcseconds

    • Standard Error of Parallax / Parallax (the relative distance precision rdp)

    • Johnson B - V Color Index

    • Effective Temperature in Kelvins
To check how many stars have passed the querying process successfully, see the Q parameter in the status bar at the bottom of the main window.

Adjusting Sizes of Points Depicting Stars

As mentioned in the trouble with the scale, it is not possible to define the sizes of points with a proportional scale. Thus, from this point of view, the best method which has the closest relationship to reality is to use a same size for all points, that is, the smallest pixel of a monitor. Another method is to employ the star's apparent brightness in order to get more interesting views, but there is always a compromise between the quality of a rendered image and performance of rendering. Because we prefer the performance, there are only six predefined sizes of points corresponding to the six magnitude classes as defined by Hipparchus, a Greek astronomer, around 150 BC. All stars brighter than first magnitude stars are depicted as first magnitude stars; all stars fainter than sixth magnitude stars, as sixth magnitude stars.

To select the appropriate method, use the Define Sizes of Points Depicting Stars options in the Main Control Panel.
  • To use a same size for all points depicting stars, select the option By Same Size for All Stars and choose a size between 1 and 6. The value 1 corresponds to the largest size, whereas the value 6 corresponds to the smallest size--the smallest pixel of a monitor in a given screen resolution.
  • To use the sizes defined by the apparent brightness as seen from the Sun, select the option By Apparent Magnitude from the Sun.
  • To use the sizes defined by the apparent brightness as seen from your position, select the option By Apparent Mag. from Your Position.
  • To use the sizes defined by absolute magnitude (a measure of luminosity), select the option By Absolute Magnitude. In this case, the classification into the six predefined sizes is as follows:
    Size 1: Mv < -10

    Size 2: -10 <= Mv < -8
    Size 3: -8 <= Mv < -6

    Size 4: -6 <= Mv < -4

    Size 5: -4 <= Mv < -2

    Size 6: Mv >= -2
Displaying On Screen Details

To display some useful details directly on the screen, use the On Screen Details options in the Main Control Panel.
  • To mark the Sun's position, check the box Mark Sun's Position.
  • To display names of famous stars, check the box Display Names of Famous Stars.
    (To change this option directly from the main window, press F6.)
  • To mark the extent of our Milky Way Galaxy as a simplified wireframe, check the box Mark Extent of Our Milky Way Galaxy as Simplified Wireframe. This option is especially useful to realize what a small fraction of our Galaxy is mapped in visible light; to do this, fly somewhere outside our Galaxy and then orbit around the galactic center.
    (To change this option directly from the main window, press F7.)
  • To display some details of each star, check the box Display Details of Each Star and check the boxes of the required parameters.
    There are these selectable parameters in the control panel:

    • Catalogue Identifier
    • Right Ascension and Declination
    • Apparent Visual Magnitude (as seen from the Sun)
    • Absolute Visual Magnitude
    • Trigonometric Parallax
    • Distance from the Sun
    • Johnson B - V Color Index
    • Effective Temperature

    The parameters appear on the right side of each displayed star, in the order in which they are selected in the control panel. The corresponding units are indicated by the suffixes of the parameters' values. To distinguish the apparent visual magnitude, absolute visual magnitude, and Johnson B - V Color Index, the apparent visual magnitude has the suffix 'm', the absolute visual magnitude has the suffix 'M', and the Johnson B - V Color Index has no suffix.
    Use this option only when there are a few stars displayed on the screen; otherwise, you will receive a strange screen full of green numbers.
Displaying Information about a Selected Star

To learn more about a star rendered on the screen, place the mouse pointer over the star and double-click the left mouse button. If there is only one star rendered on the screen, the Information about This Marked Star window will appear immediately; otherwise, the Star Selection dialog box will appear, containing up to ten nearest stars from the position of the mouse pointer. In the Star Selection dialog box, you can select the correct star by these parameters: Catalogue ID, Right Ascension, Declination, Apparent Visual Magnitude (as seen from the Sun), Trigonometric Parallax, DFYP--Distance from Your Position, and Name. As soon as you select the correct star, the Information about This Marked Star window will appear, and the selected star will be marked by a violet cross.

The Information about This Marked Star window contains several stellar parameters, but there are only parameters employed by AstroFly in order to reduce the required amount of RAM and the size of database files, especially in the case of the star database derived from the Tycho Catalogue. If you need some other parameters, like proper motions, astrometric and photometric standard errors, spectral types, etc., use the complete Hipparcos and Tycho Catalogues. As mentioned in the trouble with the space-time, time is not employed in AstroFly; thus, right ascension and declination are given at the original catalogue epoch, that is, J1991.25, within the International Celestial Reference System (ICRS).

There are a few useful buttons at the bottom of the Information about This Marked Star window:
  • Click the Use It as Destination in Astro-Fly-Through button in order to send the position of the marked star into the Astro-Fly-Through Control Panel as the Destination parameters. Then you can click the Fly Now button of the control panel in order to move there immediately--of course the star will be eliminated, for it would be a threat to your journey.
  • Click the Use It as Center of Orbital Motions button in order to center the marked star on the screen and to adjust the Radius of Orbital Motions in Parsec parameter in the Astro-Fly-Through Control Panel. Then you can freely orbit around the star.
  • Click the Show It in H-R Diagram button in order to check the position of the marked star in the Hertzsprung-Russell diagram.
Checking a Star in the Hertzsprung-Russell Diagram

To check a star in the Hertzsprung-Russell diagram, open the Information about This Marked Star window for the star, as described above, and then click the Show It in H-R Diagram button. As soon as you click the button, the rendering mode of the main window will be switched from the 3D model to the Hertzsprung-Russell diagram, and the position of the star in the Hertzsprung-Russell diagram will be marked by a violet cross.

To return to the 3D model rendering mode of the main window, close the Information about This Marked Star window, or click the Return to 3D Model button.

The Filtering Stars is also available in the Hertzsprung-Russell diagram rendering mode.

Finding a Star

To find a star by its name or catalogue identifier, choose Tools > Find Star, or double-click the right mouse button and choose Find Star from the popup menu. In the Find Star By dialog box, select and define the appropriate parameter, and then click the Find It button. When the star is found, it is centered on the screen, and the Information about This Marked Star window appears.

Studying Constellations

This is a funny feature of AstroFly, intended as an easy way to realize how the famous stars constituting the familiar constellations are located in space.

To study constellations, use the Constellations Control Panel. There are three check boxes of each constellation. The first, in the Show Lines of Selected Constellations column, specifies whether the lines of the constellation are displayed. The second, in the Show Names of Selected Constel. column, specifies whether the name of the constellation is displayed. The third check box, in the Study Selected Constellation column, has a special function: When you check it, the name and lines of the selected constellation are displayed, the constellation itself is centered on the screen, and the Radius of Orbital Motions in Parsec parameter in the Astro-Fly-Through Control Panel is adjusted so that you can easily orbit around the constellation. When you uncheck it, the name and lines of the constellation are hidden; it is unchecked automatically when you check another.

There are also four buttons in the Constellations Control Panel:
  • Click the Show Lines and Names of All button in order to display lines and names of all the constellations.
  • Click the Hide Lines and Names of All button in order to hide lines and names of all the constellations.
  • Click the Show Lines of All button in order to display lines and hide names of all the constellations.
  • Click the Show Names of All button in order to display names and hide lines of all the constellations.
To display or hide lines and names of all the constellations directly from the main window, press F5.

The lines of all the constellations are based on the Hipparcos Catalogue; thus, use this feature only when the Star Database Derived from HIPPARCOS Catalogue option is selected.

Switching Star Databases

This version of AstroFly works with two star databases based on the Hipparcos and Tycho Catalogues. To switch the databases, choose File > Star Database Derived from HIPPARCOS Catalogue or File> Star Database Derived from TYCHO Catalogue. When you switch the databases, your position and direction are not changed.

The star database derived from the Tycho Catalogue is not included in the AstroFly 3.0 Basic Package; it must be installed additionally if you want to use it. For more information visit the AstroFly Home Page.

Using Control Panels

The control panels are intended for easy control of AstroFly. They can remain displayed on top of other windows while you work with the main window, and any change made in a control panel has immediate effect. There are three control panels in AstroFly:
  • Astro-Fly-Through Control Panel

    To open it, choose Control Panels > Astro-Fly-Through Control Panel.
    It enables you to change your position and to adjust two parameters of motions:

    • To change your position, enter a new destination, and then click the Fly Now button. Your position and direction are changed immediately; the new direction of the line of sight is adjusted to face toward the Sun. There are these Destination parameters:

      • RA in Degrees--right ascension in degrees (ICRS)
      • DE in Degrees--declination in degrees (ICRS)
      • DFTS in Parsecs--distance from the Sun in parsecs

    • The Speed Factor of Translational Motions parameter enables you to adjust the mouse sensitivity during translational motions. Its valid range is from 0.01 to 10000.

    • The Radius of Orbital Motions in Parsec parameter enables you to specify the actual radius of orbital motions. The entered value of the parameter must be between 1 and 1000000 pc.

    There are also two buttons:

    • Click the Return Home button to return to the Sun when you get lost in space.

    • Click the Use Default Settings button to restore all the parameters of the control panel to the original state.
  • Constellations Control Panel

    To open it, choose Control Panels > Constellations Control Panel.
    It enables you to study constellations.
Configuring Environment Options

To open the Environment Options dialog box, choose Tools > Environment Options. There are these configurable parameters of the AstroFly environment:
  • The Define Colors of Points Depicting Stars By options enable you to select how the points that depict stars are painted.

    • The White Color for All Stars option specifies the white color for all stars rendered on the screen.

    • The Yellowish Color for All Stars option specifies the yellowish color for all stars rendered on the screen.

    • The Effective Temperature option specifies that each star rendered on the screen is painted with a color corresponding to its effective temperature. The computation of the effective temperature is based on the relation between the Johnson B-V color index and effective temperature for main sequence stars (Zombeck, 1990, pp. 68-69). To compute the chromaticity coordinates x, y, and z, a star is approximated by a black body radiator with its effective temperature, and Planck's radiation law and the CIE 1931 Standard Colorimetric Observer (CIE, 1986, table 2.1) are utilized. The RGB values are converted from the chromaticity coordinates by using the sRGB primaries (Stokes at al., 1996) and a non-standard white point (x = 0.3158, y = 0.3258), which is very close to the D65 white point. (This non-standard white point significantly simplifies the computation.) If the star is not a main sequence member, its color is also slightly incorrect (see the trouble with the temperature).

    • The Gamma Correction options enable you to select the gamma correction that compensates the nonlinearity of your monitor. Because this computation of gamma correction by AstroFly adversely impacts its performance, use these options only when it is impossible to specify the gamma correction at the output of your graphics card.

      • The None option specifies that no gamma correction is imposed by AstroFly.

      • The sRGB option specifies gamma correction based on the sRGB transfer function (Stokes at al., 1996).

      • The Rec. 709 option specifies gamma correction based on the Rec. 709 transfer function (ITU, 2002).
  • The Prefer Right Ascension and Declination Expressed In options enable you to select the preferred units of right ascension and declination:

    • Sexagesimal Units ( h m s, ± ° ' " )
    • Decimal Degrees
  • The Enable Line Antialiasing option of the OpenGL Settings specifies whether lines rendered on the screen are antialiased. If you prefer antialiasing, use this option rather than the full scene antialiasing feature of your graphics card.

References

CIE. (1986). Colorimetry. 2nd ed. Publication CIE 15.2-1986. (Vienna, Austria: CIE).

ESA. (1997). The Hipparcos and Tycho Catalogues. ESA SP-1200. (Noordwijk: ESA).
(Data files are also available online from the CDS: http://cdsweb.u-strasbg.fr/hipparcos.html).

Hoffleit, D.; & Warren, W. H., Jr. (1991). The Bright Star Catalogue. 5th revised ed. (Preliminary version). Yale University Observatory. (Also available online from the CDS: http://cdsweb.u-strasbg.fr/viz-bin/Cat?V/50).

ITU. (2002). Recommendation ITU-R BT.709-5. Parameter Values for the HDTV Standards for Production and International Programme Exchange. (Geneva: ITU).

Stokes, M.; et al. (1996). A Standard Default Color Space for the Internet - sRGB. http://www.w3.org/Graphics/Color/sRGB.html (retrieved 16 June 2000).

Zombeck, M. V. (1990). Handbook of Space Astronomy and Astrophysics. 2nd ed. (Cambridge, UK: Cambridge University Press). (Also available online from the ADS: http://adswww.harvard.edu/books/hsaa/).