Author Archives: James

About James

James is the Planetarium Astronomer at the Houston Museum of Natural Science. He teaches students every school morning in the planetarium, and also answers astronomy questions from the public.

Party with the planets this Memorial Day: See the closest gathering of any three planets until 2021

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As you celebrate this upcoming Memorial Day weekend, take some time to appreciate an interesting sight in the sky — the gathering of Mercury, Venus and Jupiter low in the west-northwest at dusk.

Right now, you notice Jupiter setting in the west at dusk. It outshines all stars we ever see at night, so it’s quite visible even during twilight. Because Earth is about to pass around the far side of the Sun from Jupiter’s position, we see Jupiter get a little lower to the horizon each night this month.

Image courtesy of earthsky.orgImage courtesy of earthsky.org

Perhaps, if your northwest horizon is clear enough, you will also notice Venus below and a bit to the right of Jupiter. In late January 2013, we lost sight of Venus as it began to pass around the far side of the Sun. Now in May 2013, it has begun to come from behind the Sun so that we see it again. Unlike Jupiter, then, Venus gets a little higher in the sky each night. Venus will be an evening star for the rest of 2013.

Mercury is usually invisible to us because it is always in the Sun’s general direction. Only rarely is Mercury far enough from the Sun in our sky to be above the horizon while the Sun is not. June 2013 is one of those exceptional moments. As May 2013 ends, Mercury also enters the evening sky alongside Venus.

On May 23, Mercury is directly beside Venus as both planets are 5 degrees (the width of three fingers, held at arm’s length) to the lower right of Jupiter. By May 26, Mercury and Venus have caught up with Jupiter to form a triangle about two degrees wide. (Jupiter and Mercury are side by side; Venus is the ‘apex’ pointing down.)  On the next night, Memorial Day, we see Venus and Jupiter less then one degree apart, with Mercury about two degrees above them. This will be the closest gathering of any three planets until January 2021.

Keep in mind that to observe any of this, you need a northwest horizon utterly clear of buildings, trees, or other obstacles. You can test your chosen observation site by watching a sunset there. The three planets will appear in the same direction in which the Sun sets. If you can watch sunset all the way until the Sun sets, you’ve picked a good site for observing the May 2013 planet gathering.

Keep in mind that Venus and Jupiter outshine all stars we ever see at night. This means that they become quite visible in twilight. Once you’ve picked a good observation spot, you can begin looking for Venus and Jupiter in twilight (around 8:30 p.m.) without waiting until twilight ends (about 9:15 p.m. at the end of May in Houston).

During June 2013, Mercury and Venus remain in the western sky at dusk, while Jupiter drops into the glare of the Sun. At first, the faster Mercury races out ahead of Venus and is thus higher in the sky. By mid-month, though, Mercury has begun to come around to our side of the Sun, so we see it slow down and head back towards the Sun.  On June 18, Mercury and Venus are side by side once again. Then Mercury drops back into the Sun’s glare, leaving Venus as the planet visible in the west at dusk for the rest of 2013.

Seeing Stars with James Wooten: May 2013

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Jupiter is now lower in the west at dusk. Face west at dusk and look for the brightest thing there (unless the Moon is also there), as Jupiter outshines all other stars we ever see at night. It appears slightly lower in the sky each night, though, and is gone by the end of the month. As Jupiter leaves the evening sky, Mercury and Venus emerge to join it on Memorial Day weekend. The three planets form a tight triangle May 25-26; Venus and Jupiter are just one degree apart on May 27.

Saturn is now an evening object, shining in the southeast at dusk.  Although not as bright as Jupiter, it does outshine the stars around it, so you can’t miss it.

Mars is still out of sight on the far side of the Sun this month.

Sky Map: May 2013A swath of brilliant winter stars sets in the west at dusk. Orion, the Hunter, is still visible in the west as May begins. His two dogs, represented by Sirius and Procyon, are to his left.  To Orion’s right is Taurus, the Bull, with Aldebaran as its eye. Gemini, the Twins, are above Orion. The Big Dipper is above the North Star, with its handle pointing to the right. From that handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars are in the east and southeast at dusk. Leo, the Lion, passes almost overhead in late evening.

As Orion and Taurus set, look for Antares, brightest star of Scorpius, the Scorpion, to rise in the southeast. At the same time, Vega, brightest star of the Summer Triangle, appears low in the northeast. These stars remind us that summer is on the way.

Moon Phases in May 2013:

Last Quarter                 May 2, 6:16 am; May 31, 1:59 pm
New                              May 9, 7:31 pm
1st Quarter                   May 17, 11:35 pm
Full                                May 24, 11:26 pm

The New Moon of May 9 passes in front of the Sun, causing an eclipse. However, the Moon is too far from the Sun to block it completely; the result is an annular eclipse, in which a ring of the Sun’s disk surrounds the Moon. Also, the event is visible only along a path that begins in Australia and extends across the Pacific.

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. I generally do one such tour on short May nights.

To enjoy the stars in any weather from the comfort of the HMNS Planetarium, click here for a full schedule.

Seeing Stars with James Wooten: April 2013

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Jupiter is now lower in the west at dusk. Face west at dusk and look for the brightest thing there (unless the Moon is also there), as Jupiter outshines all stars we ever see at night.

Saturn shifts from morning to evening sky this month. It rises at about 9:45 p.m. on April 1 and is in the south-southwest by dawn. On April 28, Earth passes between the Sun and Saturn, causing Saturn to rise at dusk and set at dawn. In this alignment, called opposition, Saturn is up literally all night long.

Sky Map April 2013

Venus and Mars are still out of sight on the far side of the Sun this month.  Mars is behind the Sun (in conjunction with the Sun) on April 17.

Brilliant winter stars shift toward the west during April. Dazzling Orion is in the southwest at dusk. His three-starred belt is halfway between reddish Betelgeuse and bluish Rigel.  Orion’s belt points northward to Aldebaran in Taurus the Bull. This winter and spring the Bull also contains Jupiter. To Orion’s upper left are the twin stars Castor and Pollux, marking the heads of Gemini, the Twins. You can find Sirius, the brightest star we ever see at night, by drawing a line from Orion’s belt towards the south.  To Orion’s left, forming a triangle with Sirius and Betelgeuse, is Procyon, the Little Dog Star.

Meanwhile, the stars of spring are high in the east and overhead. Look for Leo, the Lion, high in the east at dusk.  Also, extend the Big Dipper’s handle to ‘Arc to Arcturus’ and then ‘speed on to Spica’ — these stars are in the east.

Moon Phases in April 2013:

Last Quarter                  April 2, 11:38 pm
New                               April 10, 4:38 am
1st Quarter                    April 18, 7:31 am
Full                                April 25, 2:59 pm

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.

Saturday, April 13, is a special “Observe the Planets” night at the George. Come join us in observing Jupiter and Saturn!

To enjoy the stars in any weather from the comfort of the HMNS Planetarium, click here for a full schedule.

Comet Pan-STARRS is here! Catch a glimpse tonight at twilight — it’s kind of a big deal

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During the next few weeks, Comet Pan-STARRS will grace our skies as a naked-eye comet. As its name indicates, astronomers discovered this comet on June 6, 2011, using the Panoramic Survey Telescope and Rapid Response System, a planned array of telescopes in Hawaii. This array’s primary mission is to detect near-Earth objects (comets and asteroids with orbits near Earth’s) that pose a risk of impact. Of the four telescopes planned for the array, only the first, PS1, is yet operational. This is the telescope used to discover the comet.

Viewers south of the equator have been observing Pan-STARRS since February, as the geometry of its orbit has favored southern observers until now. However, as Pan-STARRS approached perihelion late on March 9, it also comes up through the plane of Earth’s orbit, making it visible from right here in Houston during mid-March 2013.

via Discover Magazine
Image via Discover Magazine

What are comets?

Comets are made of ice and dust and are often called ‘dirty snowballs.’ They are believed to be left over from the formation of the solar system. Long-period comets such as this one originate in the Oort Cloud, located about 50,000 times as far from the Sun as the Earth.  As comets approach the sun, ice changes into gas and the dust embedded within the ice is released. A cloud of particles expands out to form a coma around the comet’s solid nucleus. This coma may be 100,000 miles across. Radiation pressure of sunlight and the powerful solar wind sweep gases and dust away from the comet’s head into a tail spreading millions of miles behind the comet and pointed away from the Sun. Comets have bluish gas tails and yellowish dust tails.

Where should I look?

Face to the west during late evening twilight, which is about 8 p.m. once Daylight Saving Time begins. On March 12, a thin crescent Moon will be to the lower right of the comet. Pan-STARRS will shift towards the north (to the right as you face west) each night. This shift towards the north means that Pan-STARRS always sets soon after the Sun and is visible only during evening twilight. You will therefore need a clear, unobstructed horizon to the west when observing right at dusk. Note that by the time Pan-STARRS appears in our sky, it is already receding from the Sun, and thus getting a little dimmer each day. Most likely, Pan-STARRS will fade from view by April. How long can you follow it?

What should I look for?

Look for a fuzzy spot, not a single point of light. Observers south of the equator have reported the comet’s total brightness as a little brighter than the Big Dipper’s stars. However, the comet always appears low to the horizon and in twilight; the thicker atmosphere and brighter background will make it dimmer. While Pan-STARRS is visible, the Moon goes from crescent to full, which will dim the comet. Past comets, such as Hale-Bopp in 1997, have shown long, extended tails.

However, Australian observers in early March reported a compact appearance for the comet, with a tail visible only up to two or three degrees from the head of the comet. (Your fist held at arm’s length blocks 10 degrees.) This appearance concentrates more of the comet’s brightness in a small area of sky, making it easier to see a against a twilight sky. Comet tails have a fainter look, comparable in brightness to the Milky Way band. Binoculars may help you locate the tail if you can’t make it out with the naked eye in the twilight.

Will I ever see this again?

No one has ever seen Pan-STARRS before, and no one alive today will see Pan-STARRS again.  By all indications, this comet has traveled from the Oort Cloud into the inner solar system for the first time ever.  And once it’s gone, it won’t return for another 110,000 years.  However, Pan-STARRS could be just the ‘warm-up act’ for a much bigger and brighter comet in November and December 2013 — comet ISON.

Comets are notoriously unpredictable, though; there’s no telling if ISON will meet expectations.  It’s better to take advantage of clear skies forecast for this week and look for Pan-STARRS. When you see it, you’ll be looking at one of the oldest, most pristine objects of our solar system.