Seeing Stars with James Wooten: Comet ISON, Winter Solstice & the Geminid meteor shower

ev.owaThis is it. The final stargazing report of 2013. So let’s get to it, shall we?

Venus remains in the west at dusk for one more month. It outshines everything but the Sun and Moon, so you can begin observing it during deep twilight. Shortly after the new year begins, Venus shifts from the evening to the morning sky.

Jupiter will be up literally all night long early next month. In December 2013, then, it is not up at dusk but rises during the evening. Now you can see it rise in the northeast at about 8 p.m., just as Venus sets. By New Year’s Eve, Jupiter rises by 5:50 p.m., during twilight.

Mars remains in the morning sky. It continues to brighten a bit in the south at dawn.

Saturn has reappeared in the pre-dawn sky. Face southeast right before sunup to see it.

In December, the Big Dipper is below the horizon at dusk. As the Big Dipper sets, though, Cassiopeia rises. This is a pattern of five stars in a distinct W shape which lies directly across the North Star from the Big Dipper. Look for Cassiopeia high in the north on fall and winter evenings.

The Summer Triangle sets in the west. Watch for the Great Square of Pegasus almost overhead at dusk now and in the west by Christmas. Taurus, the bull, rises in the east. Look for the Pleiades star cluster above reddish Aldebaran. Dazzling Orion, the hunter, rises shortly after dusk (by month’s end, it is already up at dusk). As Orion enters the evening sky, we transition from the relatively dim evening skies of autumn to the brilliant stars of winter.

Unfortunately, it appears that Comet ISON did not survive its close passage to the Sun this past Thanksgiving. At 12:48 p.m. CST on Thurs., Nov. 28, ISON passed just 1.7 solar radii above the Sun’s surface. This proved to be too close, as the Sun’s gravity tore ISON apart, causing it to shed much of its gas and dust. This left only a small remaining fragment to continue on ISON’s orbital path, a fragment too small to put on a naked-eye show on December mornings. Binocular observers, though, can still give it a try.

You can still find information showing ISON’s position, or you can view the full path.

If ISON survives perihelion this Thanksgiving (it has about a 50/50 chance), we could see it quite well between Thanksgiving and Christmas. More on this in the December update.

Moon Phases in December 2013:

New: December 2, 6:21 pm
1st Quarter: December 9, 9:12 am
Full: December 17, 3:28 am
Last Quarter: December 25, 7:49 am

At 11:11 a.m. on Sat., Dec. 21, the Sun is directly overhead at the Tropic of Capricorn, the farthest point south where this is possible. This puts the Sun as low as possible in our sky, and marks the winter solstice. In the Southern Hemisphere, the Sun is as high as possible in the sky — this is the summer solstice for them.

Although the winter solstice is the shortest day, the earliest sunset occurred on about Dec. 2, and the latest sunrise will occur Jan. 10. That’s because the Earth speeds up on its orbit as it approaches perihelion (closest approach to the Sun) next month. This acceleration shifts sunrise, local noon, and sunset slightly later each day this month and next. The effect is smaller than that of the Sun taking a lower path across the sky, which normally dominates in causing earlier sunsets and later sunrises. But the Sun’s apparent path varies very little near the solstice itself, allowing the secondary effect of the Earth approaching the Sun to predominate. For most people, then, (those who witness sunset but sleep through sunrise), days will seem to lengthen throughout December, although they don’t really begin lengthening until Dec. 21.

The Geminid meteor shower peaks this month, as it does every December. Along with the Perseids in August, the Geminids are one of the two most reliable meteor showers, producing on average about 100 meteors per hour. The Geminids are unique among meteor showers because they are associated not with a comet but with an asteroid, 3200 Phaethon. This means that with Geminids, we see significant activity much earlier in the night than with other showers.

Most meteor showers peak in the hours immediately before dawn. This is because what plows through the debris field is the leading edge of the Earth, and that’s the side going from night into day. Since Phaethon is an asteroid, however, debris along its orbital path forms a shallower angle to Earth’s orbital path, meaning that we begin to face into the debris field as early as 9 or 10 p.m. Meteors will seem to “radiate” from the constellation Gemini, hence the name of the shower. However, they may appear anywhere in the sky.

As always, you see more meteors the farther you are from big city lights, which hide dimmer ones. Our George Observatory will be open at 5 p.m. on Friday night, Dec. 13, to 1 a.m. on Saturday morning, Dec. 14, for observing this meteor shower.

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement.

Comet ISON Sprouts a Double Tail

Today’s guest post is written by John Moffitt, Astrophysicist & HMNS Volunteer.

Amateur astronomers are getting a better look at Comet ISON as it dives toward the sun for a Nov. 28th close encounter with solar fire. As the heat rises, the comet brightens, revealing new details every day. This photo, taken Nov. 10th by Michael Jäger of Jauerling Austria, shows a beautiful double tail. One tail is the ion tail. It is a thin streamer of ionized gas pushed away from the comet by solar wind. The filamentary ion tail points almost directly away from the sun.

Comet Ison gets a double tail - 111013 - crop

The other tail is the dust tail. Like Hansel and Gretel leaving bread crumbs to mark their way through the forest, ISON is leaving a trail of comet dust as it moves through the solar system. Compared to the lightweight molecules in the ion tail, grains of comet dust are heavier and harder for solar wind to push around. The dust tends to stay where it is dropped. The dust tail, therefore, traces the comet’s orbit and does not point directly away from the sun as the ion tail does.

Comet ISON is currently moving through the constellation Virgo low in the eastern sky before dawn. Shining like an 8th magnitude star, it is still too dim for naked eye viewing, but an increasingly easy target for backyard optics. Amateur astronomers, if you have a GOTO telescope, enter these coordinates.

Four comets visible in the pre-dawn eastern sky. Look with binoculars before the sun comes up.

4 comets skymap - 111213

Comet ISON Briefings at HMNS

November 29 – December 1

To find out whether Comet ISON survives its close encounter with the Sun and how to see it in December’s morning sky, come to the Burke Baker Planetarium Friday through Sunday of Thanksgiving weekend. An ISON update will precede each Planetarium show!
PLANETARIUM LECTURE
“Tracking Comet ISON and Other Possible IMPACTS”
Thursday, December 5, 6 p.m.
Tickets $18, Members $12
Comets and asteroids that roam the inner solar system and are a possible threat to Earth. Comet ISON will be grazing the Sun on November 28, and if it survives, it may come within our view. Dr. Sumners will give an update on Comet ISON and other incoming objects. Includes viewing of the show Impact!

Click here for tickets and more information on the Comet ISON briefings.

Seeing Stars with James Wooten: the Comet ISON & the end of Daylight Saving Time

Only one more month left in the year!

In November, Venus remains in the west at dusk. It outshines everything but the Sun and Moon, so you can begin observing it during deep twilight.

Jupiter is high in the morning sky this month. Look for it high in the west at dawn.

You can also look for Jupiter in the late evening sky in the east. It rises by 11:10 p.m. on November 1, and by 8:10 p.m. on November 30.

Mars, much dimmer than Jupiter, now pulls away from it in the morning sky. It now brightens a bit in the east at dawn.

Saturn is behind the Sun (at conjunction) on November 6, and thus out of sight most of the month. By Thanksgiving, you can try finding it low in the southeast at dawn.

november2013

This star map shows the Houston sky at 10 p.m. CDT on November 1, 8 p.m. CST on November 15, and 7 p.m. on November 30. To use the map, put the direction you are facing at the bottom. The Summer Triangle is high in the west. This consists of the brightest stars in Cygnus, Lyra, and Aquila. The ‘teapot’ of Sagittarius sets in the southwest, with Venus to its right. Pegasus, the Flying Horse, is high in the east. To the south and east, we see a vast dim area of stars known as the “Celestial Sea,” where only Fomalhaut stands out.

This month, the Big Dipper is to the lower left of the North Star at dusk, and soon sets. As a result, it may be hard to see if you have trees or buildings north of you. As the Big Dipper sets, though, Cassiopeia rises. This is a pattern of five stars in a distinct W shape which lies directly across the North Star from the Big Dipper. Look for Cassiopeia high in the north on fall and winter evenings.

Perhaps the most significant sight in our skies this month will be Comet ISON. That’s perhaps because ISON has never been in the inner solar system before and will never come back, so astronomers are unsure how it will behave.

There is some optimism, however, that ISON will brighten enough to be visible to the naked eye as it approaches the Sun this Thanksgiving Day. On Thanksgiving, when ISON is at its brightest, it will be too close to the Sun to observe. But you might notice it low in the southeast at dawn in the weeks leading up to Thanksgiving Day. You’ll be looking for a dim, diffuse object, so you’ll want to pick a site far from city lights and a morning with little or no moonlight. ISON passes close to the Star Spica on November 17.

With the help of the Internet, you can track ISON’s position, or view ISON’s full path.

If ISON survives perihelion this Thanksgiving (it has about a 50/50 chance), we could see it quite well between Thanksgiving and Christmas. I’ll have more on this in the December update.

Moon Phases in November 2013:
New:  November 3, 6:48 am
1st Quarter:  November 9, 11:58 pm
Full:  November 17, 9:15 pm
Last Quarter:  November 25, 1:29 pm

Sunday, November 3, is the first Sunday of the month. Accordingly, Daylight Saving Time ends at 2 a.m. that morning. (At 2 a.m., the time reverts to 1 a.m., such that the 1 a.m. hour happens twice). Remember to set all clocks back one hour on Saturday night, November 2, and enjoy your extra hour of sleep!

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement.