Some daily events in the changing sky for October 19 – 27.
Huge Outburst of Comet Holmes. On October 24th news flashed around amateur networks that faint little Periodic Comet Holmes (17P) had undergone an enormous outburst — and was shining at about magnitude 2.5, easily visible to the naked eye. The presumed ejection of gas and dust was still so close to the comet's nucleus as to appear almost starlike, as if this were a nova rather than a comet. The cloud of ejected stuff is expected to enlarge into a more traditional cometary appearance in the next several days.
The comet had been magnitude 17! Such wild behavior has a precedent, though; Holmes was also in a great outburst when it was discovered in 1892, reaching 5th magnitude. Back then, in fact, it had two such eruptions; the second came 2 1/2 months after the first.
See our article.
Comet LONEOS. A much lesser little comet is currently visible in binoculars — sort of, with difficulty — just above the western horizon in the end of twilight. Comet LONEOS, C/2007 F1, is about 5th magnitude, nearly at its predicted peak. It's heading southeast (leftward above the dusk horizon as seen from mid-northern latitudes) day by day. Telescopes have shown it with a pale gray-green head and a long, thin gas tail. Ephemeris; charts; pictures.
Friday, October 19
Saturday, October 20
Sunday, October 21
Monday, October 22
Tuesday, October 23
Wednesday, October 24
Thursday, October 25
Friday, October 26
Saturday, October 27
Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly foldout map in each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).
Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of maps; the standard is Sky Atlas 2000.0) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion by Strong and Sinnott, the even more detailed Night Sky Observer's Guide by Kepple and Sanner, or the enchanting though somewhat dated Burnham's Celestial Handbook). Read how to use them effectively.
More beginners' tips: "How to Start Right in Astronomy".
This Week's Planet Roundup
Mercury is hidden in the glare of the Sun.
Venus (magnitude –4.6, in Leo) blazes high in the east before and during dawn. Above it are much fainter Saturn and Regulus, as shown at the top of this page. A telescope shows that Venus is at its not-quite-half-lit phase.
Mars (magnitude –0.4, in the feet of Gemini) now rises around 10 p.m. daylight saving time. It shines very high toward the south before and during dawn — near the zenith, in fact, for mid-northern observers. The "Red Planet" is actually much more like yellow-orange or even pure yellow, especially when its atmosphere is dusty. How does Mars appear to you?
In a telescope, Mars is currently 11 arcseconds in diameter. It will reach 15.9" diameter around its Christmas-season opposition. The Martian dust storms of July and August have abated, and while the planet's atmosphere is still bright and hazy with dust, surface features are showing through somewhat better. But they're still low-contrast.
Jupiter (magnitude –1.9, in southern Ophiuchus) glares low in the southwest during twilight. It sets about an hour after dark.
Saturn (magnitude +0.8) is the brightest "star" above brilliant Venus in the dawn. Fainter Regulus (magnitude +1.4) is there too, upper right of Saturn.
Uranus (magnitude 5.8, in Aquarius) and Neptune (magnitude 7.9, in Capricornus) are well placed in the south during evening. Finder charts for them are in the July Sky & Telescope, page 60, and online. With a big scope you can shoot for their faint moons! See the October Sky & Telescope, page 69.
Pluto (magnitude 14.0, in Sagittarius) is disappearing into the sunset.
All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's midnorthern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) equals Universal Time (UT, UTC, or GMT) minus 4 hours.
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