Around the Sky in 28 Days – Day 13

Running late here so I won’t be writing much about the Moon and its surroundings tonight. Tomorrow we’ll examine the Moon, Jupiter and Uranus all in a tight formation.

Around the Sky in 28 Days – Day 12

In a few nights the Moon will be not only be Full but will be in conjunction with Jupiter (and even much fainter Uranus). Till then watch as the Moon creeps closer to brilliant Jupiter every night.

Tonight the Moon is among the faint stars of Aquarius. Even under the darkest sky, the constellation of Aquarius is not much to look at. From most bright sites, few if any of its stars will be visible with a nearly Full moon in the way.

Around the Sky in 28 Days – Day 11

The Moon is traversing  a region of the sky devoid of many bright stars. If it weren’t for brilliant Jupiter, many folks in bright cities might not see much in this part of the sky. Luckily there is a single bright star located to the south and east (lower left) of the Moon. Its isolation has led it to be referred to as the “lonely star of autumn”.

Fomalhaut (Arabic for “mouth of the fish”) is located in the constellation Piscis Austrinus (the “southern fish”). It is the 18th brightest star in the sky at magnitude +1.2. Shining with a solid white light, Fomalhaut is a young A-type star twice as massive as the Sun and 18 times as bright. It is also one of the closer stars only being located at a distance of 25 light-years.

Recent observations by the Hubble Space Telescope has revealed much about Fomalhaut’s “solar system”. As the image below shows, Fomalhaut possesses a bright dust disk, probably produced by an equivalent of our solar system’s Kuiper belt. Unlike most exoplanetary systems where planets are indirectly deduced, Fomalhaut has one of the few planets ever directly seen in an exosolar system.

Image of the Fomalhaut system taken with the Hubble Space Telescope. Credit: NASA, STSCI.

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The planet, now tagged Fomalhaut b, orbits Fomalhaut in 872 at an average distance of 115 AU. Its mass is loosely constrained to be between 0.05 and 3 Jupiter masses. An infrared excess at the position of ‘b’ suggests that 20-40 Jupiter masses worth of material is orbiting the planet so it is likely it has or is forming a collection of moons not unlike Jupiter’s. Since the orbit of the ‘b’ does not exactly match the shape of the dust disk, it has been suggested that additional unseen planets are also involved in sculpting the dust disk. Of all the stellar systems out there, this may be the funniest one to watch as new telescopes and imaging technologies come online.

Around the Sky in 28 Days – Day 10

This evening (Sept 18) the Moon is in the middle of Capricornus and can still be used to find the double-double combo of Alpha and Beta Cap. If you observe a few hours after sunset, look towards the southeast to find Jupiter. Over the next few days watch as the Moon closes in on the “King of Planets”.

Meteor Activity Outlook for September 18-24, 2010

The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.

September offers longer nights in the northern hemisphere that tend to be less hazy than those experienced in mid-summer. In the sky, no major showers are visible from either hemisphere but the northern hemisphere enjoys the advantage of higher sporadic rates. Most of the shower activity this month is produced from the Perseus-Aurigid complex active this time of year. These showers rarely produce more than five meteors per hour but still manage to produce most of the shower activity seen this month. Unfortunately the Perseus-Aurigid complex lies too low in the northern sky for southern hemisphere observers to view very well. Video studies have shown that the Southern Taurids are visible as early as September 7th therefore after this date the Antihelion radiant will no longer be listed until the Taurid showers end in December. The Antihelion meteors are still active but their radiant is superimposed upon that of the more numerous Taurids, therefore it is impossible to properly separate these meteors. Observers in the southern hemisphere suffer from some of their lowest rates of the year this month. The Southern Taurid radiant is not too badly placed so observers south can expect to see a little of this activity this month.

During this period the moon reaches its full phase on Thursday September 23rd. At this time the moon will be located opposite the sun and will rise as the sun sets and sets as the sun rises. This weekend the waxing gibbous moon will set during the early morning hours and will allow a short window of opportunity between moonset and morning twilight to view meteor activity under dark conditions. The estimated total hourly rates for evening observers this week is ~2 from the northern hemisphere and ~1 from the southern hemisphere. For morning observers the estimated total hourly rates should be ~16 from the northern hemisphere and ~6 as seen from the southern hemisphere. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning September 18/19. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately five sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near two per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near fourteen per hour as seen from rural observing sites and three per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Morning rates are slightly reduced due to moonlight.

The following showers are expected to be active this week:

Southern Taurids (STA)

The center of the large Southern Taurid (STA) radiant lies at 00:56 (014) +05. This position lies in southern Pisces, three degrees southeast of the fourth magnitude star Delta Piscium. Since the radiant is so large, any meteor from Pisces, western Cetus, or southwestern Pegasus could be a candidate for this shower. The radiant is best placed near the meridian near 0200 LDT, but activity may be seen all night long. Striking the atmosphere at 29 km/sec., the average Southern Taurid meteor travels slowly through the skies. Rates this week should be near two per hour no matter your location.

Nu Eridanids (NUE)

Many radiants in the region of Eridanus and Orion have been suspected this time of year. Recent studies have verified a radiant active in Eridanus and moving on into Orion from September 3rd through the 24th with maximum activity occurring on the 6th. The Nu Eridanid (NUE) radiant is currently located at 05:00 (075) +06. This position lies in western Orion, five degrees west of the second magnitude star Bellatrix (Gamma Orionis). Old time observers may recall a radiant active in Orion this time of year called the Sigma Orionids. This may be a verification of that activity. The radiant is best placed near 0500 LDT, when it lies highest above the horizon in a dark sky. Rates should less than one per hour this week. With an entry velocity of 68 km/sec., most activity from this radiant would be swift. With the radiant lying close to the celestial equator, these meteors are seen equally well from both hemispheres.

The list below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.

Shower Name                 RA     DEC   Vel     Rates
                                         km/s   NH    SH
STA Southern Taurids      00h 56m  +05    30     2     2
NUE Nu Eridanids          05h 00m  +06    68    <1    <1

RA - Right Ascension
DEC - Declination
Vel - Velocity relative to Earth (in km per sec)
Rates - Rate of visible meteors per hour from a
        dark site
NH - Northern Hemisphere
SH - Southern Hemisphere

Around the Sky in 28 Days – Day 9

For the past 2 days the Moon was traversing Sagittarius, which is a Centaur archer or a teapot depending upon how you see it. For the next few days the Moon will travel among the stars of Capricornus, a half fish half goat but really just looks like a sack of potatoes to those lucky enough to observe from skies dark enough to even see the constellation.

Still for a faint constellation it has a lot going for it and a few faint naked eye (or bright binocular) stars are within a star hoop from the Moon. Alpha and Beta Capricorni make a wide double star just to the upper left of the Moon. A closer examination of both stars find that each is also part of an even closer double pair.

Beta Cap (also called Dabih) is magnitude +3.1 with a much fainter magnitude +6.1 companion. Both are easily seen and separated with a pair of binoculars. The two stars are located at a distance of 330 light-years from us and 21,000 AU from each other. The fainter star, Dabih Minor, is a class B giant with a too-close-to-be-seen F dwarf 30 AU away. The brighter star, Dahib Major, is probably a K giant with a less massive class B companion. There is even evidence of other unseen stars in the system!

Alpha Cap (also called Algedi) consists of 2 stars that can be resolved with the unaided eye. The stars are ~7 arc minutes apart, or ~1/5 the span of the Moon. Though each star is very similar in type (both G), they are not related to each other and it is just coincidence that they appear so close together on the sky. The brighter star is 109 light-years away and is 43 times more luminous than the Sun while the fainter is 6 times further away at 690 light-years and over 900 times more luminous than the Sun. For more, on Alpha Cap see the STARS site, for more on Beta Cap go here.

For tomorrow – Day 10 – I’m actually not sure yet…

Recent Discoveries – Sept 16-17, 2010

The discoveries keep rolling in as the prime discovery surveys continue to enjoy clear skies. The number of new finds should start tailing off soon as the moon approaches Full. When bright moonlight battles faint asteroids, the faint guys usually lose out.

The La Sagra Survey of Spain have reported their 4th comet discovery (all in the past 2 years). Comet La Sagra is a short-period comet with a very asteroidal orbit. In fact, the orbit is smack in the middle of the Main Belt of asteroids making this comet one of the few known Main Belt comets (MBC). This type of comet represents a intermediate state between usually dry asteroids and icy comets. The rapidly increasing number of MBCs means that many asteroids (especially in the mid- to outer-belt) still retain some volatiles that occasionally sublimate to produce cometary activity. At 18-19th magnitude this comet is not expected to get brighter and should fade as it moves away from the Sun and Earth. The comet was discovered with La Sagra’s CCD-equipped 0.45-m (18″) reflector.

2010 RC130 will brighten up to magnitude 15.0 on October 3 as it closes to within ~10 times Lunar Distance.

Asteroid    Type     MOID     a     e     i     H  Mag  Discoverer      MPEC
2010 SJ     Aten    0.050   0.92  0.17  11.5  23.3  19  Catalina        2010-S14
2010 SH     Amor    0.150   1.58  0.31  23.1  23.2  20  Mount Lemmon    2010-S13
2010 SF     Aten    0.014   0.84  0.22   9.4  25.6  18  Catalina        2010-S09
2010 SE     Apollo  0.008   1.05  0.29  20.2  24.1  18  Catalina        2010-S08
2010 SD     Apollo  0.021   1.36  0.40   3.4  24.8  19  Mount Lemmon    2010-S07
2010 SC     Amor    0.025   1.56  0.34   3.3  26.0  20  Mount Lemmon    2010-S06
2010 SB     Amor    0.208   2.90  0.59   7.5  21.9  20  Mount Lemmon    2010-S05
2010 RK135  Amor    0.056   2.46  0.57   4.5  25.6  21  Mount Lemmon    2010-S12
2010 RD130  Apollo  0.024   1.99  0.55   2.2  25.3  21  Mount Lemmon    2010-S04
2010 RC130  Apollo  0.032   2.45  0.58   9.2  21.6  18  LINEAR          2010-S03
2010 RB130  Amor    0.020   2.15  0.52   1.0  24.1  18  Catalina        2010-S02

Comet       Type       T        q     a     e     i  Mag  Period MPEC
P/2010 R2 (La Sagra)
            MBC   2010-06-25  2.62  3.10  0.15  21.4  18   5.46  2010-S11

Type
Aten -  Earth crossing with semi-major axis (avg distance from Sun) < 1 AU
Apollo - Earth crossing with semi-major axis (avg distance from Sun) > 1 AU
Amor - non-Earth crossing with perihelion distance < 1.3 AU
JFC - Jupiter family comet
HFC - Halley family comet
LPC - Long-period comet
MBC - Main belt comet

T - Date of Perihelion
MOID - Minimum Orbit Intercept Distance, minimum distance between asteroid and Earth's orbit
a - semi-major axis, average distance from Sun in AU (1 AU = 93 million miles)
e - eccentricity
i - inclination
H - absolute magnitude
Mag - magnitude at discovery
Discoverer - survey or person who discovered the object
MPEC - Minor Planet Electronic Circular, the discovery announcement
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