See the 6 or 7 Brightest Night Objects

The last week of February and first few days of March offer a rare opportunity to people at mid-northern latitudes: the chance to see the night sky's six or seven brightest objects simultaneously 30 to 60 minutes after sunset. These are (in order of brightness):

the Moon (seriously bright!)
Venus (magnitude -4.3)
Jupiter (magnitude -2.2)
Sirius (magnitude -1.4)
Mars (magnitude -1.2)
Mercury (see below)
Canopus (south of latitude 37°N)

You will need a site with an unobstructed horizon to the west (for Mercury) and east (for Mars). People who hope to see Canopus will also need an unobstructed horizon to the south.

The timing for this observation is determined by Mercury, which is setting in the west at dusk. The later in the evening you observe, the darker the sky will be, but the lower Mercury will be. 45 minutes after sunset might be a good compromise.

All the objects in the list except for Mercury look better as the sky grows darker. Venus, Jupiter, Sirius, and the Moon remain above the horizon for several hours after sunset, and Mars rises higher as the evening progresses, peaking around midnight.

The best dates for the observation are toward the end of the window of opportunity, in early March. That's because Mars appears higher in the east each evening, while Mercury remains near its highest throughout the first week of March.

However, Mercury fades during the period, starting around magnitude -1.2 in late February, fading below Canopus (magnitude -0.7) around March 3d, and fading below Alpha Centauri (magnitude -0.3) around March 5th. That ends this viewing opportunity, since Alpha Centauri is only visible from the Southern Hemisphere at this time of year.

This opportunity is made possible by the coincidence of several factors. Venus and Jupiter are both high in the evening sky. Mercury is enjoying its best evening apparition of 2012 for northern viewers. Mars is almost at its closest to Earth for this orbit — the only time it counts among the night sky's 7 brightest objects. And this all takes place when Sirius and Canopus are near the highest in the early evening.

Canopus is visible anywhere south of latitude 37° north, assuming that you have an unobstructed southern horizon. The sky scene at right shows Canopus from latitude 34° north — roughly accurate for Los Angeles and Atlanta.

In case you're wondering, the northern limit for viewing the 6 brightest objects is around the Arctic Circle, beyond which Sirius becomes invisible. And the southern limit to achieve the feat without optical aid is around the equator. South of that, the angle of the ecliptic is so shallow that it's very difficult to spot Mercury.

However, people at mid-southern latitudes can probably see the night sky's eight brightest objects, including Alpha Centauri, 15 to 30 minutes after sunset in early March if they use binoculars, making it possible to catch both Mercury and Mars low in the twilight glow.

People all over the world should keep watching Venus and Jupiter as they approach each other during the first two weeks of March.

Faraway Eris is Pluto's Twin

In November 2010, the distant dwarf planet Eris passed in front of a faint background star, an event called an occultation. These occurrences are very rare and difficult to observe as the dwarf planet is very distant and small. The next such event involving Eris will not happen until 2013. Occultations provide the most accurate, and often the only, way to measure the shape and size of a distant Solar System body.

The candidate star for the occultation was identified by studying pictures from the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory. The observations were carefully planned and carried out by a team of astronomers from a number of (mainly French, Belgian, Spanish and Brazilian) universities using — among others — the TRAPPIST [1] (TRAnsiting Planets and PlanetesImals Small Telescope, eso1023) telescope, also at La Silla.

“Observing occultations by the tiny bodies beyond Neptune in the Solar System requires great precision and very careful planning. This is the best way to measure Eris’s size, short of actually going there,” explains Bruno Sicardy, the lead author.

Observations of the occultation were attempted from 26 locations around the globe on the predicted path of the dwarf planet’s shadow — including several telescopes at amateur observatories, but only two sites were able to observe the event directly, both of them located in Chile. One was at ESO’s La Silla Observatory using the TRAPPIST telescope, and the other was located in San Pedro de Atacama and used two telescopes [2]. All three telescopes recorded a sudden drop in brightness as Eris blocked the light of the distant star.

The combined observations from the two Chilean sites indicate that Eris is close to spherical. These measurements should accurately measure its shape and size as long as they are not distorted by the presence of large mountains. Such features are, however, unlikely on such a large icy body.

Eris was identified as a large object in the outer Solar System in 2005. Its discovery was one of the factors that led to the creation of a new class of objects called dwarf planets and the reclassification of Pluto from planet to dwarf planet in 2006. Eris is currently three times further from the Sun than Pluto.

While earlier observations using other methods suggested that Eris was probably about 25% larger than Pluto with an estimated diameter of 3000 kilometres, the new study proves that the two objects are essentially the same size. Eris’s newly determined diameter stands at 2326 kilometres, with an accuracy of 12 kilometres. This makes its size better known than that of its closer counterpart Pluto, which has a diameter estimated to be between 2300 and 2400 kilometres. Pluto’s diameter is harder to measure because the presence of an atmosphere makes its edge impossible to detect directly by occultations. The motion of Eris’s satellite Dysnomia [3] was used to estimate the mass of Eris. It was found to be 27% heavier than Pluto [4]. Combined with its diameter, this provided Eris’s density, estimated at 2.52 grams per cm3 [5].

“This density means that Eris is probably a large rocky body covered in a relatively thin mantle of ice,” comments Emmanuel Jehin, who contributed to the study [6].

The surface of Eris was found to be extremely reflective, reflecting 96% of the light that falls on it (a visible albedo of 0.96 [7]). This is even brighter than fresh snow on Earth, making Eris one of the most reflective objects in the Solar System, along with Saturn’s icy moon Enceladus. The bright surface of Eris is most likely composed of a nitrogen-rich ice mixed with frozen methane — as indicated by the object's spectrum — coating the dwarf planet’s surface in a thin and very reflective icy layer less than one millimetre thick.

“This layer of ice could result from the dwarf planet’s nitrogen or methane atmosphere condensing as frost onto its surface as it moves away from the Sun in its elongated orbit and into an increasingly cold environment,” Jehin adds. The ice could then turn back to gas as Eris approaches its closest point to the Sun, at a distance of about 5.7 billion kilometres.

The new results also allow the team to make a new measurement for the surface temperature of the dwarf planet. The estimates suggest a temperature for the surface facing the Sun of -238 Celsius at most, and an even lower value for the night side of Eris.

Trusty Comet Garradd - Observing Highlights

Comet Garradd and M71
Comet Garradd passed M71 in Sagitta on the evening of August 26th.

Comet Elenin has been getting a lot of press in recent months — and now it seems almost certain to be a total bust. Meanwhile, people in the know have been following a comet that has never been hyped much, but seems almost certain to be a fine, though not spectacular performer for many months to come.

We're talking about Comet C/2009 P1 Garradd. At the end of August it was already a fine sight through telescopes of all sizes, shining high in the evening sky at 7th magnitude. It has a bright head, a sharp starlike nucleus, and a tail that's stubby but well defined. And it's forecast to shine near its 6th-magnitude best all the way from October to mid-March. Not since Hale-Bopp has any comet remained so bright for so long.

Comet Garradd passes through the Coathanger asterism on the evening of Friday, September 2nd, then crosses the northwest corner of Sagitta, and soon enters Hercules, where it will remain until February. That means it’s high in the west after nightfall in October, lower but still in good view in November, and near the west-northwest horizon at the end of twilight around Christmas. But by then it’s already up higher in the east before the first light of dawn; the best viewing tips from evening to morning on December 16th.



Path of Comet Garradd Oct 2011 - Jan 2012
Comet Garradd crosses Vulpecula and Sagitta in early September, then remains in Hercules for the next six months.

As the comet climbs high in the early-morning sky of January and February, it will pass the Keystone of Hercules, skim ½° by the globular cluster M92 on the morning of February 3rd (mark your calendar), then sail northward past the head of Draco. It should stay bright all the way into spring as it returns to the evening sky.

Why is it changing so slowly? Comet Garradd is unusually large and distant as 6th-magnitude comets go. It never comes closer to the Sun than Mars’s average distance; at perihelion on December 23rd it’s 1.55 astronomical units from the Sun. Nor does the comet ever come near Earth; it’s about 2 a.u. from us all through October and November, and when closest next March 5th it will still be 1.27 a.u. away. Too bad! Garradd might have qualified for “Great Comet” status if had been on a trajectory to pass close to the Sun and if Earth weren’t on the wrong side of its orbit at the time.

Astronomer Gordon J. Garradd discovered the comet at 17th magnitude on August 13, 2009, at Australia’s Siding Spring Observatory while hunting for — ironically — near-Earth objects.

Supernova in M101

Supernova in M101. The new Type Ia supernova is still brightening in M101, the Pinwheel Galaxy off the Big Dipper's handle. Supernova 2011fe was discovered on August 24th at magnitude 17.2, reached 13.8 on the 25th, 12.5 on the 27th, and 11.6 on the 29th. By then it was easier to see than the galaxy itself in amateur telescopes through suburban light pollution. On the evening of August 31st it was up to about magnitude 10.8.

A normal Type Ia supernova at M101's distance, 23 million light-years, should reach magnitude 10.0 at its peak, assuming none of its light is lost to interstellar absorption in M101 itself. It's well within visual reach in a 4-inch scope. You'll be using the supernova to find the galaxy, not the other way around!

Moonlight will increasingly return to the evening sky starting around September 3rd or 4th.

Opportunity Reaches Its New Home

The west rim of Endeavour Crater, seen from outside
A portion of the west rim of Endeavour crater sweeps southward in this color view
from NASA's Mars Exploration Rover Opportunity. Click for full-size image.
It shouldn't be long until Opportunity is peering over the rim inside.

Yet another adventure is about to begin for NASA’s Mars Exploration Rover B, more famously known as Opportunity. The golf-cart-size, solar-powered vehicle reached the outer hills of its new destination, Endeavour crater, on August 9th after a 3-year, 13-mile (21-km) trek across the flat Martian terrain from the previous big crater it explored, Victoria.

The site from which Opportunity radioed Earth has been named “"Spirit Point,” in memory of its smaller twin, Spirit, that collected data on Mars from January 2004 to March 2011.

Launched in 2003, both Spirit and Opportunity were expected to complete a 90-Martian-day mission; instead, Opportunity has endured 30 times longer and traversed a total of 20.81 miles. Since touching down south of the Martian equator on January 25, 2004, the rover has explored five craters: Eagle, Endurance, Erebus, Victoria, and Santa Maria.

Endeavour, its new destination, is huge: 14 miles (22 km) wide — 25 times as large as Victoria, whose geology the rover studied for two years. A spectrometer aboard NASA’s Mars Reconnaissance Orbiter has detected clay minerals inside Endeavour, which likely formed during a warmer and wetter period on the Red Planet.

"We're soon going to get the opportunity to sample a rock type the rovers haven't seen yet," says science-team member Matthew Golombek (Jet Propulsion Laboratory, Pasadena, California).

Mission scientists will next choose the safest way to have Opportunity descend into the crater. There’s no word on how long they expect this epic exploration to last.

However, we do know that Opportunity's larger successor, Curiosity, will soon be launched on its way to Gale crater on another side of Mars.

2011 Perseid Meteor Showers

The Perseid meteor shower is an annual meteor shower that is extremely regular in its timing and can potentially be visible for weeks in the late summer sky, depending on weather and location.

The Perseid meteor shower is named after the constellation Perseus, which is located in roughly the same point of the night sky where the Perseid meteor shower appears to originate from. This is a useful naming convention, but not very accurate!

The source of the Perseid meteor shower is actually debris from the comet Swift-Tuttle. Every year, the earth passes through the debris cloud left by the comet when the earth's atmosphere is bombarded by what is popularly known as "falling stars."

When and where to look for Perseids in 2011

In 2011, visibility (the weather also notwithstanding) will be somewhat limited by a full moon on August 13 which will likely wipe out fainter meteors from view.

Because of the way the earth hits this debris cloud, the Perseid meteor shower is much more visible in the Northern hemisphere.

People in Canada, for instance, can see the meteor shower by mid-July, but generally there isn't much activity at such an early date. Throughout Europe, the US and the rest of North America, meteor shower activity usually peaks sometime around August 12th, when it is not unusual to see at least 60 meteors per hour streaking across the Northeast sky.

The meteors are certainly bright, but they are actually only tiny objects, usually no more than a grain of sand. However, as they travel at speeds of up to 71 kilometers per second, these small particles put on quite a brilliant show.

The Perseid meteor showers were observed as far back as two thousand years ago, and in ancient Europe, the Perseid meteor shower was known as the "Tears of St. Lawrence."

How to view Perseids

Today, the best place to observe the Perseid meteor shower (or any meteor shower for that matter), is somewhere dark, away from light pollution, and with the moon out of the field of vision. The less light visible, the more brilliant the meteor shower will be.

Telescope or camera?

While mostly viewable to the naked eye, the annual Perseid meteor show may be partially obstructed by the moon, clouds or night mist, so amateur astronomers may want to carry along a pair of binoculars or a camera with a telescopic lens. Even on clear nights, some kind of viewing aid comes in handy for catching sight of even the faintest of falling stars, aptly named "telescopic" meteors. Experts usually just advise to forget the telescope, and simply look up toward the northeast sky.

For photographing the annual event, a digital camera mounted on a tripod helps to steady the images that swiftly move across the sky. A quick trigger finger also helps. Even random clicks during the height of Perseid "prime-time" will guarantee that you'll catch something! Be sure to have the camera focused on infinity and, if your camera permits, leave the shutter open for several minutes for the most spectacular photographic effects.

New Video Showing Water Maybe Flowing on Mars

Scientists believe they have found water on Mars after finding that lines on the planet's surface are more visible in warm seasons.

Scientists announced on Thursday that they saw dark, finger-like features appearing and extending down some Martian slopes during late spring through summer, which fade in the winter and return during next spring.

These recurring features were located on several steep slopes in Mars' southern hemisphere, according to NASA, and are believed to be briny water.

"The best explanation for these observations so far is the flow of briny water," said Alfred McEwen of the University of Arizona, Tucson, in a statement. McEwen is the principal investigator for the orbiter's High Resolution Imaging Science Experiment, or HiRISE, and the lead author of a report about the recurring flows published in Thursday's edition of the journal Science.

Water flows that appear in spring and summer on a slope inside Mars' Newton crater are shown in this combination of orbital imagery with 3-D modeling in this NASA handout photo released to Reuters August 4, 2011. This image has been reprojected to show a view of a slope as it would be seen from a helicopter inside the crater, with a synthetic Mars-like sky. The source observation was made May 30, 2011, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. Color has been enhanced.


This series of images shows warm-season features that might be evidence of salty liquid water active on Mars today. Evidence for that possible interpretation is presented in a report by McEwen et al. in the Aug. 5, 2011, edition of Science. These images come from observations of Horowitz crater, at 32 degrees south latitude, 141 degrees east longitude, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. In time, the series spans from late summer of one Mars year to mid-summer of two years later. The images taken from oblique angles have been adjusted so that all steps in the sequence show the scene as if viewed from directly overhead. The features that extend down the slope during warm seasons are called recurring slope lineae. They are narrow (one-half to five yards or meters wide), relatively dark markings on steep (25 to 40 degree) slopes at several southern hemisphere locations. Repeat imaging by HiRISE shows the features appear and incrementally grow during warm seasons and fade in cold seasons. They extend downslope from bedrock outcrops, often associated with small channels, and hundreds of them form in rare locations. They appear and lengthen in the southern spring and summer from 48 degrees to 32 degrees south latitudes favoring equator-facing slopes. These times and places have peak surface temperatures from about 10 degrees below zero Fahrenheit to 80 degree above zero Fahrenheit (about 250 to 300 Kelvin). Liquid brines near the surface might explain this activity, but the exact mechanism and source of the water are not understood.


This series of images shows warm-season features that might be evidence of salty liquid water active on Mars today. Evidence for that possible interpretation is presented in a report by McEwen et al. in the Aug. 5, 2011, edition of Science. These images come from observations of a steep crater slope in the Terra Cimmeria region of Mars, at 38.8 degrees south latitude, 159.5 degrees east longitude, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. In time, the series spans from the end of summer of one Mars year to mid-summer of two years later. The images taken from oblique angles have been adjusted so that all steps in the sequence show the scene as if viewed from directly overhead. The features that extend down the slope during warm seasons are called recurring slope lineae. They are narrow (one-half to five yards or meters wide), relatively dark markings on steep (25 to 40 degree) slopes at several southern hemisphere locations. Repeat imaging by HiRISE shows the features appear and incrementally grow during warm seasons and fade in cold seasons. They extend downslope from bedrock outcrops, often associated with small channels, and hundreds of them form in rare locations. They appear and lengthen in the southern spring and summer from 48 degrees to 32 degrees south latitudes favoring equator-facing slopes. These times and places have peak surface temperatures from about 10 degrees below zero Fahrenheit to 80 degree above zero Fahrenheit (about 250 to 300 Kelvin). Liquid brines near the surface might explain this activity, but the exact mechanism and source of the water are not understood.


This series of images shows warm-season features that might be evidence of salty liquid water active on Mars today. Evidence for that possible interpretation is presented in a report by McEwen et al. in the Aug. 5, 2011, edition of Science. These images come from observations of Newton crater, at 41.6 degrees south latitude, 202.3 degrees east longitude, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. In time, the series spans from early spring of one Mars year to mid-summer of the following year. The images have been adjusted to correct those taken from oblique angles to show how the scene would look from directly overhead. The features that extend down the slope during warm seasons are called recurring slope lineae. They are narrow (one-half to five yards or meters wide), relatively dark markings on steep (25 to 40 degree) slopes at several southern hemisphere locations. Repeat imaging by HiRISE shows the features appear and incrementally grow during warm seasons and fade in cold seasons. They extend downslope from bedrock outcrops, often associated with small channels, and hundreds of them form in rare locations. They appear and lengthen in the southern spring and summer from 48 degrees to 32 degrees south latitudes favoring equator-facing slopes. These times and places have peak surface temperatures from about 10 degrees below zero Fahrenheit to 80 degree above zero Fahrenheit (about 250 to 300 Kelvin). Liquid brines near the surface might explain this activity, but the exact mechanism and source of the water are not understood. The series is timed to dwell two seconds on the first and last frames and one second on intermediate frames, though network or computer performance may cause this to vary.