Sky At Totality

The total phase of an eclipse is accompanied by the onset of a rapidly darkening sky whose appearance resembles evening twilight about 30 to 40 minutes after sunset. The effect presents an excellent opportunity to view planets and bright stars in the daytime sky. Aside from the sheer novelty of it, such observations are useful in gauging the apparent sky brightness and transparency during totality. The Sun is in Pisces and all five naked eye planets as well as a number of bright stars will be above the horizon for observers within the umbral path. Figure 25 depicts the appearance of the sky during totality as seen from the center line at 11:00 UT. This corresponds to western Romania near the point of greatest eclipse.

Mercury (mv=+0.7) and Venus (mv=­3.5) are located 18° west and 15° east of the Sun, respectively, and both will be easily visible during totality. Venus is two months past inferior conjunction while Mercury is one month shy of superior conjunction. As the brightest planet in the sky, Venus can actually be observed in broad daylight provided that the sky is cloud free and of high transparency (i.e., no dust or particulates). Look for the planet during the partial phases by first covering the crescent Sun with an extended hand. Venus will be shining so brightly, it will be impossible to miss during totality. Mercury will prove much more challenging, but not too difficult if the sky transparency is good. Under the right circumstances, it should be possible to view all five classical planets, the Moon and the Sun (or at least its corona) as one's eyes sweep across the darkened sky during totality. A number of the brightest winter/spring stars may also be visible during totality. Regulus (mv=+1.35) is 10° east of the Sun while Castor (mv=+1.94) and Pollux (mv=+1.14) stand 31° and 28° to the northwest. Procyon (mv=+0.38) and Sirius (mv=-1.46) are located 30° and 52° to the southwest, respectively. Betelgeuse (mv=+0.5v) and Rigel (mv=+0.12) are low in the southwest at 26° and 38°, while Aldebaran (mv=+0.85) is 20° above the western horizon. Capella (mv=+0.08) lies 63° to the northwest. Finally, Arcturus (mv=+1.94) lies due east 30° above the horizon.

The following ephemeris [using Bretagnon and Simon, 1986] gives the positions of the naked eye planets during the eclipse. Delta is the distance of the planet from Earth (A.U.'s), V is the apparent visual magnitude of the planet, and Elong gives the solar elongation or angle between the Sun and planet.

Planetary Ephemeris: 1998 August 11 11:00:00 UT
Equinox = Mean Date
ObjectRADecDeltaVSize (")Phase Elong (°)
Sun09h23m08s+15°19´42" 1.01358-26.71893.6
Mercury08h07m35s+18°08´56" 0.82062 0.78.2 0.3018.3W
Venus10h06m46s+04°18´35" 0.30047-3.555.5 0.0415.4E
Mars14h55m32s-18°28´03" 1.068140.38.8 0.8688.5E
Jupiter02h11m31s+11°47´36" 4.61411-2.142.7 0.99103.7W
Saturn03h00m28s+14°34´31" 9.133830.118.2 1.0091.5W

For sky maps from other locations along the path of totality, see the special Web site for the total solar eclipse of 1999 August 11.

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