![]() ![]() This effect is particularly important for the Moon, which can be as large as 1°, but small for the Sun (≤ 8.8") and planets. The difference between the geocentric and topocentric position is called the diurnal parallax or geocentric parallax. Topocentric distance of the Moon is the distance between the Moon's center and the observer. For example, the geocentric distance of the Moon is the distance between Moon's center and Earth's center. In the popup box, the term "elongation" is the angular separation of the planet and the Sun as seen from Earth "heliocentric" refers to quantities measured from the Sun's center "geocentric" refers to quantity measured from Earth's center "topocentric" refers to quantities measured from the observer's location. They can also be clicked and a popup box will appear. Sun, Moon and planets are displayed on the charts by symbols indicated above. The constellation is determined by the constellation boundaries established by the Belgian astronomer Eugène Delporte in 1930 on behalf of the International Astronomical Union (IAU). The second constellation has "(year number)" added to it, indicating the constellation in that particular year. The first one has "(2000)" added to it, indicating the present constellation. In that case, two constellations are given. In the distant past and distant future, some nearby stars are seen to move far away from their present constellations. Outside the time interval 3000 BCE - 3000 CE, only proper motion is included in the J2000.0 position and only precession and proper motion are included in the "of date" position. The apparent position with respect to the true equator and equinox of date are corrected for precession, nutation, and aberration of light in addition to proper motion and parallax. When the time is between 3000 BCE and 3000 CE (CE = common era), positions of the stars with respect to J2000.0 mean equator and equinox are corrected for proper motion and annual parallax. The popup box shows further information about the star. Stars in the charts can be clicked and a popup box will appear. However, it should be noted that stereographic projection is not designed to model the Moon illusion and so the distortion should not be regarded as a faithful representation of human perception. This feature might not be as bad, since constellations do appear bigger when they are close to the horizon because of the Moon illusion. This effect is quite noticeable in animations showing the diurnal motion of the sky. For example, a constellation is about twice as big when it is near the horizon than when it is near the zenith. However, the mapping does not preserve area. The mapping is conformal and shapes are preserved over a small area. Stereographic projection is commonly used in sky maps. The star charts are created using the stereographic projection with the nadir as the projection point. 0° means north is at the top, south at the bottom (useful for looking at stars near the southern horizon) 90° means east is at the top, west at the bottom (useful for looking at stars near the western horizon) 180° means south is at the top, north at the bottom 270° means west is at the top, east at the bottom. ![]() The azimuth-at-the-top parameter is used to rotate the star chart, which is convenient for laptop and desktop users since the device's screens can't be rotated easily. When the Day/Night button is active, the background color of the star chart is determined by the Sun's position in the chart: light purple when the Sun is above the horizon, gradually changes to black when the Sun is below the horizon and black when the Sun is 18° below the horizon. ![]() #Star chart date fullThe full names of the constellations are listed on this webpage. The default settings can now be changed by filling in a formĬonstellation labels, when active, are shown in the abbreviated form. ![]() Sidereal times and star charts at other locations and times can be obtained by clicking the Locations and Times button at the top of the page and filling in the form. The two default locations are at longitude 88.2434°W, latitude 40.1164°N (Champaign, IL, USA) and at longitude 88.2434°W, latitude 30°S. This webpage uses the computer's clock to obtain the current local time and then uses it to calculate the local sidereal times and plot star charts on two locations. Constellation List CANVAS NOT SUPPORTED IN THIS BROWSER! ![]()
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