Observing the Solar System
Photo courtesy Bill Arnett, author of the excellent WWW site "The Nine Planets" http://www.seds.org/billa/tnp/
This module includes basic notes for observing the objects of our solar system. Observing info is provided in both a simple, narrative form, and also as detailed position - observing notes [go straight to 2001-2005 planetary database] (necessary for the planets not visible to the naked eye, comets, and asteroids). Some great photos and videos are included.
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Links to a separate
multimedia page on each planet
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©1986 Paul McGehee
Leaving aside the sun, the earth and its moon, five planets are considered "naked eye" objects: Mercury, Venus, Mars, Jupiter and Saturn. Uranus is sometimes JUST visible to the naked eye under excellent seeing conditions. Neptune requires a telescope to see, and Pluto - Charon are quite unspectacular even in large telescopes.
Venus and Jupiter can often be observed fairly well using only binoculars -- Venus' phases, and Jupiter's four brightest moons, can be seen in (steady) binoculars. Saturn's rings require a telescope. Excepting infrequent bright comets, comets and asteroids require a moderate size telescope.
The moon is quite spectacular in binoculars and telescopes of all sizes.
NEVER OBSERVE the sun directly -- permanent eye damage - blindness will occurs after less than one second's observation, even with binoculars !!
Finding planets -- interior vs. exterior
Mercury and Venus are called "interior" planets because their orbits are between the sun and the earth's orbit. This means they are always fairly close to the sun: Mercury is never more than 28 degrees from the sun, while Venus can get up to 45 degrees from the sun. [Since the earth rotates through 360 degrees every 24 hours (approx.), objects appear to move 15 degrees per hour.] This means that Mercury always rises less than two hours before sunrise, or sets less than two hours after sunset -- usually it is much closer to the sun. The brighter (larger and closer) Venus can rise up to 3 hours before sunrise, or set up to 3 hours after sunset, and thus is MUCH EASIER to observe.
The rest of the planets are "exterior" planets because their orbits are further from the sun than the earth's orbit. Thus they can appear anywhere in the sky at different times, close to the sun or far away from it. [There are some excellent movies showing this in Starry Night Pro.]
Mars, Jupiter and Saturn are easily visible to the naked eye (except when they are close to the sun), and are great objects for small telescopes. As noted above, Uranus is usually near the limit of naked eye detection, Neptune always requires optical aids, and Pluto is very unspectacular (although many students like to be able to say "I've seen Pluto!"). In addition, binoculars will show four of Jupiter's 20 moons (the rest require large telescopes), and a small telescope will show two of Saturn's 18 moons. Uranus' and (all but one of) Neptune's moons are effectively beyond the reach of small telescopes. [Those moon counts are likely to become out of date, very soon...]
Locating Uranus, Neptune (and if you're bold, Pluto) requires careful searching using their co-ordinates and/or "finder charts" (provided in this module).
Southern Hemisphere observing tips for 2001:
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A nice parade of planets appears in the morning sky during July and August. This is what they'll look like: |
Mercury is visible (barely) in the evening sky in late January; better views are provided in the second half of September -- the best time to see it in the evening sky this year. It can be observed in the morning sky during late-Feb and March, and again in mid-July (when Venus, Jupiter and Saturn are also visible in the morning sky).
Venus dominates the western evening sky from the beginning of the year until mid-February. During late February and early March, it is a bright crescent low in the western evening sky. From mid-April through early December, it's in the morning sky -- best observed mid-April through mid-August. Venus returns to the evening sky in March 2002. The late Feruary - early March crescent, when it is "only" 48 million km from earth and has an apparent size of 52 arc seconds, is worth seeing!
Mars is visible in the morning sky from January through early May, and in the evening sky from late May through December. It is best observed in mid-June, when its apparent size is 20 arc seconds and it is "only" 68 million km from earth.
Jupiter and Saturn are visible in the evening sky from approx. February through late April. They will be in the monring sky from late July, and gradually move back to the evening sky by the end of the year. They are best observed in January and February, when they are closest to earth (a mere 645 million km and 1,275 million km, respectively).
Uranus and Neptune are visible in the morning sky from mid-March through September, and can be observed in the evening sky from October. You'll probably need the Neptune finder map. They are best observed from June through October, when they are closest to earth (2,850 million km and 4,350 million km, respectively). [During most of 2001, Neptune is actually further away from earth than is Pluto.]
Pluto is in the evening sky until November (but you need to know PRECISELY where to look, and will need AT LEAST an 8 inch telescope). You WILL need the Pluto finder map. It is best observed from late February through late September. Even in an 8 inch aperture telescope, Pluto will be a tiny, barely visible point of light (but then you can honestly say "I've seen Pluto!").
The easiest way to determine where the planets are is to use database provided or the Starry Night planetarium. See also: The Nine Planets: Observing the Solar System
Detailed Planetary Positions through 2005
I have created a database that shows each planet's position (Right Ascension and Declination), week by week, as well as practical observing notes, throughout the end of 2005:
View the database (includes detailed explanations and teachers' notes)
I calculated them using the US Naval Observatory's Multi-Year Interactive Computer Almanac, available on CD-ROM (purchase -- US$ 25) or online (free):
http://mach.usno.navy.mil/cgi-bin/aa_micaform2?calc=8&ZZZ=END
Enter the starting date, interval, and iterations required (time can be ignored)
Select the object of interest.
Values are astrometric and geocentric (i.e., as if viewing from the centre of the earth) -- one can customise for a particular location if desired, by calculating topocentric rather than geocentric coordinates (not really necessary). Click here for more info.
Welcome to the Planets (JPL / NASA)
Written by Stephen R. Kessell
Updated 30 January, 2001
