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| This month's star chart looks toward
the western horizon about 10:00 PM on Oct 28. Uranus is about 40 deg above
the SW horizon, shining at mag 5.8. Under a clear dark sky, Uranus
is visible to the naked eye. Thus, it is a little surprising that the planet
was not discovered until 1781. The disk is about 4 arcseconds, so
can readily distinguish it from the images of stars.
Uranus's axis of rotation is inclined about 98 deg with respect to its orbit around the sun, so its axis lies nearly in the plane of its orbit. This inclination is the greatest of any planet in the solar system (the earth's axis is inclined about 23.5 deg.) As Uranus orbits the sun, its axis keeps a constant orientation in space. What does this do to the seasons on Uranus? At last count, Uranus has 15 satellites 10 of which were discovered by Voyager 2. (One of the others was discovered using the 82" scope at McDonald.) The orbits of the satellites are all parallel to the planet's equator, nearly perpendicular to the planet's orbit. What does this say about the possible origins of the satellites? Neptune is also visible (at mag 7.9) apparently near Uranus in the sky, with a disk of about 2 arcseconds. However, Uranus is about 20 au from the earth, and Neptune is about 30 au. How far in miles? Among other wonders, M57, the Ring Nebula, is visible high in the west. We can see it well in amateur scopes, but the view may not be quite so glorious as the HST image on our Discover the Universe Calendar (available for a small price from the BBAS). Saturn and Jupiter are visible in the eastern sky, so there's lots to see this month. Come join us! |
You can print a copy of this star chart so you can take it outside.
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