Skynotes February and March 2005

From South Dublin Astronomical Society

Current moon phase. Image from USNO.

These sky notes are updated every two months and give you the low down on what's up in the skies during the period. If there is any aspect of the notes you do not understand, or would like more comprehensive details of a particular event, then feel free to contact the author, John Flannery, at .

Links to web sites where you will find more detailed information about particular phenomena are highlighted at the end of this page. An archive of previous months skynotes is availble.

The Sun

A marvellous naked-eye sunspot group in the early part of January was extremely active and gave rise to a number of major flares which triggered aurora activity here. Although alerts were issued for a number of nights in succession, it was a typically cloudy evening when some reports filtered in of aurora displays seen in the northern part of the country on Jan 21st.

Although astronomers agree that the Sun is winding down from the most recent sunspot maximum that peaked in 2000, our nearest star still has a few surprises to leave theorists scratching their heads. The Earth is at perihelion on Jan 2nd at 01h.

Comets

Comet 141P/Machholz 2 (2005) was a nice nakedeye object for observers during the early part of January and was well placed as it headed north on the celestial sphere. As it glided by the Pleiades star cluster it presented astrophotographers with a nice opportunity to capture striking images of the comet and cluster in the same field.

141P/ Machholz 2 continues to be visible throughout most of the night as it passes from Perseus into Camelopardalis by the end of January. The comet reaches perihelion on January 24th when it will be 1.20 Astronomical Units from the Sun.

The following web sites will allow you get an ephemeris and up-to-date observations; encke.jpl.nasa.gov www.aerith.net/comet/weekly/current.html

Algol

Minima of the eclipsing variable Persei are given. The star varies in brightness between magnitude 2.1 and 3.4 in a period of 68 hours and 49 minutes.

Algol appears as a single star in Earth based telescopes but is know to consist of two stars of unequal brightness quite close to and revolving around each other. The faint one eclipses the bright one once in every orbit and so we see the light drop.

Most of the time Algol remains bright but then over a period of about ten hours it loses then regains three quarters of its light. Jan 27d 02h 42m 29d 23h 30m Feb 1d 20h 18m 19d 01h 12m 21d 22h 00m

The Planets in February 2005

Saturn continues to be well placed this month as it continues its retrograde motion amongst the stars of Gemini - the planet reaches its stationary point on March 22nd when it does an about-turn to resume its eastward, or direct, motion.

Saturn's largest moon Titan, visited by the Huygens probe in January this year, can be seen even in steadily mounted binoculars as a magnitude +8.4 'star' close to the planet. Favourable times are when it is at elongation such as at 01h on February 20th when it is at western elongation.

Jupiter rises late-evening and a small telescope will reveal the major bands that streak its atmosphere. The planet's direct motion grinds to a halt on February 2nd when it begins its retrograde loop which will carry it westward amongst the stars of Virgo until June 22nd.

Binoculars will allow you see the four large Galilean moons Io, Europa, Ganymede, and Callisto as they swing about their parent from night to night. A small telescope will let you see more. The shadow of Jupiter's globe is offset to the west of the planet at the moment which gives us some great opportunities to spy some fascinating series of eclipses of the Galilean moons. The Astronomical Almanac lists some of these while Irish amateur astronomer Gary Nugent's JupSat software www.nightskyobserver.com will also provide the relevant predictions for the interested observer.

The Moon is near Jupiter on February 28th.

Mars only brightens slightly this month and the disk is still too small to show any detail even in large telescopes.

Mercury and Venus are too close to the Sun to be visible this month.

Uranus is in conjunction with the Sun on February 25th while Neptune reaches conjunction on February 3rd (when it is actually occulted by the Sun's disk).