How does Jupiter Mahadasha affect you

Jupiter observation - even when the sky is overcast

How bright and how big does Jupiter appear to us? Bands of clouds can be observed with a spotting scope. If the weather does not cooperate, the visual impression can be simulated with a photo and a telescope.

How bright and big does the Jupiter disk appear?

Angular diameter, arcsecond and magnitude

When Jupiter, as at the time of Galileo's first observations of Jupiter, is again close to its position in opposition to the sun, it almost demands a closer look. Locator cards can be used with the Stellarium software? a virtual planetarium can be created for the school (map example "heidelberg_15_sept_2009_21_uhr.jpg"). In their opposition position, the outer planets come closest to the earth and are accordingly bright and large. For example, in September 2009 Jupiter achieved an apparent magnitude of -2.8 and an apparent size (angular diameter) of 47 arc seconds. We receive more than three times as much light from Jupiter (x) like Sirius, the brightest star we can see (magnitude = -1.5). Whoever wants to do the math, decide x in the following context: [-1.5 - (-2.8)] = -2.5 log (x).
  • Wikipedia: Apparent brightness
    The apparent brightness or magnitude (“mag” for short) indicates how bright a celestial body appears to an observer on earth.
  • Wikipedia: arcsecond
    An arcsecond is a unit of measurement of angle. Sixty arc seconds correspond to one minute of arc and 60 minutes of arc to one degree.

How big is the planet disk?

Comparison with a moon crater

The apparent size of the full moon disk is about 31 minutes of arc. The planetary disk of Jupiter showed around one fortieth of the diameter of the moon in September 2009 and thus appears in the telescope about the size of the lunar crater Copernicus. Will anyone find this crater on the moon? (See Walks on the Moon lesson, Walk 3, Fig. 3.)

Dry run on the telescope

If the sky is overcast, you do not have to do without the demonstration of the Jupiter disk. Simply print out Fig. 3 so that the Jupiter disk image has a diameter of 2.5 centimeters (scaling the image size to about 85 percent). You hang this picture on a tree (illuminate it if necessary) and observe it with a telescope from a distance of about 110 meters. Is the distance right?

Visual observation of the original

Cloud bands and flattening of the poles

Fig. 3 shows Jupiter with its moons Io and Europa (photo by Benjamin Kühne). The shadow of Io on Jupiter's surface reveals where the sun is. The two dark bands of clouds near the equator can already be seen well with small astronomical telescopes or with good spotting scopes such as those used by amateur ornithologists (from 40x magnification). The flattened shape of the planet can also be clearly seen in Fig. 3: Due to the rapid rotation (at the equator, one rotation takes less than ten hours!), The gas giant flattens out a little. Its equatorial diameter is around 144,000 kilometers, while the pole diameter is only about 135,000 kilometers.

Moons and solar eclipses on Jupiter

The four Galilean moons can already be seen with the binoculars. However, telescopes with an aperture of 15 to 20 centimeters are required to observe the shadows of the moon on Jupiter's clouds. You can find more astrophotos by Benjamin Kühne on his website:
  • Nachtwolke.de
    Homepage of Benjamin Kühne. Here you can find photos of astronomical objects and atmospheric phenomena.

Determination of the slice size

By the way, you can easily determine the size of the Jupiter disk yourself. To do this, measure the time it takes for the target to pass through a crosshair in the telescopic field of vision several times and convert the time to the angle: 360 degrees correspond to 24 hours. (Then an angle of 15 arcseconds is swept over in one second. The difference between sidereal time and the solar time available to us can be neglected here.) For example, with an average cycle time of 2.6 seconds (mean value from several measurements) for the size of the Jupiter disk obtained an angular diameter of 39 arc seconds.