Astronomy on Titan: Looking Upward

Let us now consider what one sees as one looks upward from Titan’s surface.

At first sight, it is very disappointing. All one sees is a reddish-brown haze, though a haze well above the surface. The Sun looks like a bright orange dot, but one only visible at high elevation angles, greater than about 30 – 45 degrees. But it is easily resolved with a small telescope: its angular size is 3 minutes of arc. But even when the Sun is hard to see, it would still light up the haze.

One can watch the Sun move across the sky with a period of about 16 (Earth) days, and move between 27d north and 27d south with a period of about 30 (Earth) years. As one does so, one can show that Titan is approximately spherical in another way: the Sun will be at different directions relative to different locations. One also finds that the Sun’s period is close to the Foucault-measured rotation period. So could the Sun be moving much more slowly than Titan?

There are plenty of other things to see, especially if one can get above the haze.

It would be hard to see Saturn during the daytime, but the planet would make its existence manifest in another way every 15 years, around its equinoxes. Saturn would eclipse the Sun, making around 21 eclipses each eclipse season, with the eclipses lasting as much as 6 hours.

During the night, Saturn would be borderline visible, and only if it is high in the sky. But much like the Earth from the Moon, it would stay in one spot, moving ahead and behind by 3.3d over the Sun’s period and in the Sun’s direction. It will be sizable, about 5 1/2d in angular size, about the size of one’s fist at arm’s length.

One wouldn’t be able to see Saturn’s rings, since they would be nearly edge-on, but away from Saturn’s equinoxes, the rings would cast very visible shadows on the planet’s body.

Above the haze

One can get above it by going ballooning. At 50 km altitude, the pressure is about 0.1 bar and the temperature 70 K. But the temperature then stars rising, and at about 100 km, the pressure is 0.01 bar and the temperature 120 K, The main haze layer starts here, and extends to about 200 km, with 0.001 bar and 160 K. The temperature stays at that value for the next few hundred km, and at 450 – 500 km is a detached layer of thin haze.

The record for Earth high-altitude ballooning is 53 km, with a pressure of 0.0006 bar. So getting above the main haze is feasible.

Once one does so, the view will be very rewarding. One will be able to see the stars in the daytime as well as in the nighttime, and one will also be able to see Saturn’s other moons, its rings, and the other planets.

An interesting oddity is “superrotation” of Titan’s upper atmosphere. Like Venus’s upper atmosphere, it rotates much faster than the body itself. At 60 km, its atmosphere rotates about 5 times per Titan day, and if it increases linearly up to 200 km, its period will be about 1 Earth day. So one may not be able to observe Saturn and its inner moons continuously for several Titan days.

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