Mention meteors, and casual skywatchers usually think of the annual Perseid shower on display every August.

But the Geminid meteor shower of mid-December ties or even surpasses the Perseids as the year’s richest and most reliable meteor display. Geminid meteors come from 3200 Phaethon, an asteroid discovered in 1983.

This year the Geminids are predicted to peak on Tuesday morning around 1100 GMT, more or less. That’s excellent timing for North America, especially out west. The moon that night is only a day past first quarter and sets around midnight or 1 am local time, depending on where you live.

Even before then, on Monday evening, the moonlight isn’t bright enough to dampen the shower’s visibility too much – and the Geminids, with their radiant [apparent origin] near the stars Castor and Pollux, pick up steam as early as 8 or 9 pm. But the radiant is highest around 2 am, so the morning hours are the usually the most productive.

Bundle up as warmly as you possibly can, and lie back in a dark spot with an open sky. You may see as many as two meteors a minute on average if you have a very dark sky and are watching after midnight.

If your sky is not too light-polluted, you might try making a careful meteor count and reporting it to the International Meteor Organization. Such counts by amateurs supply much of what we know about meteor showers’ behaviour. For your count to be useful, you’ll need to follow the procedures described or at the .

Don’t forget that the shower lasts more than one night. Counts are especially needed on nights away from the maximum, because fewer people are watching. In any case, enjoy the show!

Courtesy of magazine

A crude spectrum has been obtained for the atmosphere of a super-Earth orbiting a dim red dwarf star 40 light years away. The planet’s upper atmosphere is apparently dominated by steam or cloudy haze.

The star, Gliese 1214 (GJ 1214) in Ophiuchus, is 300 times dimmer than the sun. Its planet was discovered in 2009 when the detected the planet’s silhouette periodically dimming the star. The planet has 6.5 Earth masses, as determined later by the star’s gravitational wobbles, and it circles the little star very closely in just 38 hours. The transits reveal the planet’s diameter to be 2.6 times Earth’s – making its average density very low, only about a third of Earth’s density.

Using one of the European Southern Observatory’s 8.2-metre Very Large Telescope reflectors, a team of astronomers detected a telltale absorption spectrum caused by a tiny fraction of the star’s light filtering through the planet’s atmosphere during each transit. The spectrum was featureless, indicating that the upper atmosphere either consists mostly of water vapor or is dominated by high-altitude clouds or haze.

“This is the first super-Earth to have its atmosphere analysed. We’ve reached a real milestone on the road toward characterising these worlds,” said team leader Jacob Bean of the Harvard–Smithsonian Center for Astrophysics in a .

Before this observation, astronomers had suggested three possible atmospheres for Gliese 1214b. The planet could be shrouded by water – which, given its high temperature so close to the star (200 ºC), would be in the form of steam. Or it could be a rocky world with an atmosphere of mostly hydrogen obscured by high clouds or hazes. Or it might be a mini-Neptune, with a small rocky core and a deep hydrogen-rich atmosphere, the upper part of which would be clear.

The measurements clearly show no sign of hydrogen and thus rule out the third option. So the atmosphere is either rich in steam or blanketed by clouds or hazes. The planet’s low density, meanwhile, indicates that it’s a waterworld.

“Although we can’t yet say exactly what that atmosphere is made of, it is an exciting step forward to be able to narrow down the options for such a distant world to either steamy or hazy,” says Bean. “Followup observations in longer-wavelength infrared light are needed to determine which of these atmospheres exists on Gliese 1214b.”

Journal reference: (DOI: 10.1038/nature09596)

Courtesy of magazine

Some daily events in the changing sky for April 10 – 18

Forgotten but not gone? Comet Lulin remains at 9th magnitude, in the feet of Gemini in the western sky just after dark. The window of moonless early evenings begins opening around Saturday April 11th.

The Comet Yi-SWAN challenge. It isn’t much at magnitude 8.5, but this new comet is far north, crossing the bright pattern of Cassiopeia this week. It’s getting quite low in the northwest just after dusk – lower than it is in the northeast just before the first light of dawn. However, the moon was full on Thursday the 9th, so the only moonless time to look for the comet this week will be right after dusk, starting about April 11th. Next week will be better, with the comet higher before dawn (but no brighter).

Friday, April 10

• When spring began, the Big Dipper stood upright high in the northeast after nightfall, balancing on the end of its handle. Now it’s April, so the Dipper is tipping leftward. Its top two stars, forming the front of its bowl, point lower left toward rather dim Polaris, the North Star, three fist-widths at arm’s length away.

Saturday, April 11

• Sometime around 2200 daylight saving time, bright Arcturus shines at exactly the same height in the east as the bright star Capella shines in the northwest. The time of this balancing act depends on your location, especially on how far east or west you are in your time zone. How accurately can you determine when it happens at your site?

Sunday, April 12

• Before dawn Monday morning, the waning gibbous moon shines very close to Antares as seen from North America. The moon occults, or covers, Antares for Hawaii and some other Pacific islands; also parts of Mexico and New Mexico during daytime Monday morning.

• Saturn’s big moon Titan casts its black shadow onto Saturn’s globe from 0722 to 1151 GMT on the 13th; that’s 1222 to 0451 PDT on Sunday. Saturn will still be up in good view at the beginning of that time for western North America.

Monday, April 13

• As spring advances, Orion and its companions sink lower after dusk. Look for Orion in the southwest this week with his belt almost horizontal. Left of Orion shines bright Sirius. A little farther to Orion’s right is orange Aldebaran, with the Pleiades farther beyond.

Tuesday, April 14

• From winter to spring: As night falls, the winter star Sirius is lowering in the southwest while the spring star Arcturus is rising in the east. They’ll be at the same altitude above your horizon around 2000 or 2100 daylight saving time, depending on where you live in your time zone.

Wednesday, April 15

• For observers at mid-northern latitudes, Arcturus in the east shines higher at nightfall than Spica, which is off to its right in the southeast. However, if you live as far south as Miami (or Honolulu, Taipei, Calcutta, Doha, or Luxor), this isn’t so; Arcturus and Spica are about equally high at nightfall.

Thursday, April 16

• Titan orbits Saturn every 16 days. So now, about four days after it passed nearly in front of Saturn and cast its shadow onto the planet, you’ll find Titan is at its western elongation, about four ring-lengths to Saturn’s west.

Friday, April 17

• Last-quarter moon (occurs at 0936 EDT, or 1336 GMT).

• Venus is passing 6° north (upper left) of Mars, low in the east before Saturday’s sunrise.

Saturday, April 18

• During dawn Sunday morning, the waning crescent Moon hangs only 1° to 3° from Jupiter (at the time of dawn for North America).

This Week’s Planet Roundup

Mercury (about magnitude -1) has its best evening apparition of the year this week and next. Look for it low in the west about 40 minutes after sunset. It gets higher later in the week.

Venus (magnitude -4.5) is low in the dawn. Look for it above the eastern horizon about 60 to 30 minutes before sunrise. Don’t confuse it with Jupiter, higher and far to the right in the southeast. (You can find your local sunrise time in this . If you’re on daylight saving time like most of North America, make sure the Daylight Saving Time box is checked.)

In a telescope, Venus is a thickening and shrinking crescent. The best telescopic views come in full morning daylight, with Venus higher in steadier air.

Mars (magnitude +1.2) is very low in the sunrise glow, to the lower right of Venus. Use big binoculars. Good luck.

Jupiter (magnitude -2.1, in Capricornus) shines in the southeast during early dawn.

Saturn (magnitude +0.6, near the hind foot of Leo) shines high in the southeast at dusk and highest in the south around 2100 or 2200 local time. Regulus, a little less bright, sparkles 16° (roughly 1.5 fist-widths at arm’s length) to Saturn’s upper right in early evening, and more directly to its right in late evening.

In a telescope, Saturn’s rings are 4° from edge on. They’ll close to exactly edge-on next September 4th, when, unfortunately, Saturn will be out of sight practically in conjunction with the Sun.

Uranus (6th magnitude) is hidden low in the sunrise glow, in the background of Venus and Mars.

Neptune (8th magnitude) is also in the glow of dawn, in the background of Jupiter.

Pluto (14th magnitude, in northwestern Sagittarius) is in the south-southeast before the first light of dawn.

All descriptions that relate to your horizon or zenith – including the words up, down, right, and left – are written for the world’s mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) equals Universal Time (known as UT, UTC, or GMT) minus 4 hours.

Courtesy of magazine

Some daily events in the changing sky for March 27 – April 4.

Friday, March 27

• Venus is at inferior conjunction (between Earth and the Sun), passing 8° north of the Sun. See this .

Saturday, March 28

• As twilight gives way to night, look to the right of the crescent Moon in the west for the stars of little Aries (just outside the frame in this illustration). Higher to the Moon’s upper left is the Pleiades star cluster.

Sunday, March 29

• In late dusk, the Pleiades are about 7° above the crescent Moon (seen at the time of dusk for North America), as shown at right.

Monday, March 30

• This evening the Pleiades are about 7° below the Moon.

Tuesday, March 31

• A small telescope will always reveal Titan, Saturn’s largest satellite. Tonight and tomorrow Titan is three or four ring-lengths to Saturn’s west.

Wednesday, April 1

• This evening, the Moon shines just about midway between the bright stars Capella (to its right) and Procyon (to its left).

Thursday, April 2

• First-quarter Moon (occurs at 1034 EDT (1534 GMT)).

Friday, April 3

• Arcturus, the “Spring Star,” sparkles brightly in the east these evenings. After about 9 or 10 pm, look for Vega, the “Summer Star,” rising low in the northeast.

Saturday, April 4

• The Moon this evening forms a straight, diagonal line with the star Regulus and Saturn to its lower left.

This week’s planet roundup

Mercury is hidden in the glare of the Sun.

Venus (magnitude -4.0) is at inferior conjunction on March 27th. But even though it’s close to the Sun, this is an exciting time for Venus watchers! In a telescope it’s easily seen as a hairline crescent, because at this conjunction, Venus passes a full 8° to the Sun’s north.

Telescopically, Venus is best seen in full midday daylight. Just don’t let your telescope accidentally point at the Sun and blind you! Safest is to observe in the shadow of a building that will continue to block the Sun from view. For more on Venus’s especially favourable conjunction phenomena this year, see .

And already Venus is becoming visible very low in the sky of dawn. Look for it barely above the eastern horizon 10 or 15 minutes before sunrise. Don’t confuse it with bright Jupiter very far to the upper right. Find your local sunrise time from this (if you’re on daylight saving time like most of North America, make sure the Daylight Saving Time box is checked).

Mars (magnitude +1.2) is very low in the sunrise glow. Using binoculars, you can try looking for it just above the east-southeast horizon, far to the lower left of much brighter Jupiter, about 30 minutes before sunrise. Good luck.

Ceres, the largest asteroid, is magnitude 7.4 above the back of Leo.

Jupiter (magnitude –2.0, in Capricornus this year) shines low in the southeast during early dawn.

Saturn (magnitude +0.6, near the hind foot of Leo) shines in the east-southeast at dusk. It’s highest in the south around 11 pm. Look for Regulus shining 17° (nearly two fist-widths at arm’s length) to Saturn’s upper right in early evening, and more directly to its right later at night.

In a telescope, Saturn’s rings are 3.5° from edge on. The rings will open to a maximum of 4° in May, then will close to exactly edge-on next September 4th – when, unfortunately, Saturn will be out of sight practically in conjunction with the Sun.

Uranus (6th magnitude) is hidden behind the glare of the Sun.

Neptune (8th magnitude) is deep in the glow of dawn, far in the background of Jupiter.

Pluto (14th magnitude, in northwestern Sagittarius) is in the southeast before dawn.

All descriptions that relate to your horizon or zenith – including the words up, down, right, and left – are written for the world’s mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Courtesy of magazine

Some daily events in the changing sky for March 20 – 28.

Comet Lulin continues fading this week; it’s about 7th – too faint to be seen with the naked eye. But at least it’s high in the evening sky (in central Gemini) and free of moonlight until about March 29th. And its tail is ! See this and .

Friday, March 20

• At last! The equinox occured at 1144 GMT, marking the start of spring in the Northern Hemisphere (fall in the Southern Hemisphere). This is when the Sun crosses the equator heading north for the year. The Sun rises and sets nearly due east and west, and day and night are nearly equal in length.

And no, eggs do not balance on end any more easily than at any other time of year (try it). Why should they? When will this finally die?

Saturday, March 21

• With the coming of spring, the winter constellation Orion is tilting over in the southwest on the way to its seasonal departure. Accordingly, Orion’s Belt is tilting around to become more horizontal.

• At dawn Sunday morning, the waning Moon is a few degrees upper right of Jupiter.

Sunday, March 22

• Getting up before sunrise on Monday morning? Make a note to cast your gaze east-southeast for the waning crescent Moon and Jupiter to its right. Much more difficult will be faint little Mars far to the Moon’s lower left.

Monday, March 23

• For skywatchers at mid-northern latitudes, Venus should now be equally visible (or not) in the east just before sunrise and in the west just after sunset. Can you bag this double sighting?

• Another dawn challenge: Before sunrise on Tuesday morning, use binoculars to look for Mars below the thin crescent Moon just above the eastern horizon, as shown above. (They’re far to the right of Venus and, depending on your latitude, somewhat higher.)

Tuesday, March 24

• A small telescope will almost always show Titan, Saturn’s largest moon. Tonight Titan is three or four ring-lengths to Saturn’s east.

Thursday, March 26

• New Moon (occurs at 1206 EDT (1606 GMT)).

Friday, March 27

• Venus is at inferior conjunction today (at 1900 Universal Time), passing 8° north of the Sun (see this ).

Saturday, March 28

• As twilight gives way to night, look to the right of the crescent Moon in the west for the stars of little Aries. Higher to the Moon’s upper left are the Pleiades.

This week’s planet roundup

Mercury is hidden in the glare of the Sun.

Venus (magnitude -4.2) plunges down out of twilight view in the west by about March 23rd, as it swings toward inferior conjunction between Earth and Sun on March 27th.

But this is an exciting time for Venus viewers! In a telescope, Venus is a hairline crescent nearly an arcminute in diameter. And at this conjunction, Venus passes a full 8° north of the Sun. This means it should be visible at both dusk and dawn for at least three days centred on March 23rd as seen from latitude 40° north. The farther north you are, the longer the period of dawn-and-dusk visibility will be.

We’ve had reports of people with very sharp vision resolving the thin crescent of Venus with the naked eye. If you want to try, look right around sunset in a bright sky before the planet’s glare becomes a problem and it also gets too low. To reduce the effects of your eye’s optical aberrations, try looking through a small, round hole 1 or 2 mm wide in a piece of aluminium foil or cardboard. Of course, this also reduces your eye’s aperture and theoretical resolving power, so experiment with different-sized holes.

Telescopically, Venus is best seen in the afternoon daylight; it’s less glary against a bright sky, and it’s higher in steadier air. Just don’t let your telescope accidentally point at the Sun and blind you! Safest is to observe in the shadow of a building located to your west.

Mars (magnitude +1.2) is very low in the sunrise glow. Using binoculars, look for it just above the east-southeast horizon, well to the lower left of much brighter Jupiter, about 30 minutes before sunrise. Good luck.

Ceres, the largest asteroid, is magnitude 7.3 above the back of Leo (see ).

Jupiter (magnitude -2.0, in Capricornus this year) is getting a little higher in the dawn each week. Look for it low in the east-southeast about an hour before sunrise. The best telescopic views will come early in during morning twilight.

Saturn (magnitude +0.5, near the hind foot of Leo) glows in the east at dusk, well up in the southeast by midevening, and highest in the south around 11 or midnight daylight saving time. Don’t confuse Saturn with slightly fainter Regulus 18° (nearly two fist-widths at arm’s length) to its upper right in early evening, and more directly to Saturn’s right late at night.

Saturn’s rings are 3.5° from edge-on. The rings will open to 4° by late May, then will close to exactly edge-on next September 4th – when, unfortunately, Saturn will be out of sight practically in conjunction with the Sun.

P.S.: Remember the quadruple transit of Saturnian moons across the planet’s face that on February 24th? Hubble was looking, and last week the Hubble Heritage Project released the images. Wow. These are not science-fiction space art, these are photographs.

Uranus is hidden behind the glare of the Sun.

Neptune is hidden in the glow of sunrise, far in the background of Jupiter.

Pluto (in northwestern Sagittarius) is in the southeast before dawn.

All descriptions that relate to your horizon or zenith – including the words up, down, right, and left – are written for the world’s mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Courtesy of magazine