Three Planets Bunch Up In Twilight & Deep Impact

Jun 21, 2005

Gaze low to the west into the deepening twilight for the next couple of weeks and three planets will await your view. One is bright; two are fainter. You can follow them through their celestial gyrations as they shift position day by day.

The direction to look is low in the west-northwest. The brightest light shining there is Venus, the "Evening Star."

Dimmer Saturn is closing in on it from the upper left, while Mercury is closing in on it from the lower right. These three planets will form a remarkably tight bunch from June 24th to 27th, appearing close enough together to be covered by your thumb at arm's length.

After that, Saturn gets lower every day and sinks out of sight, while Venus and Mercury remain closely paired into the first week of July. The crescent Moon hangs with Mercury and Venus on July 8th. Meanwhile, the background stars Pollux and Castor add to the scene. Binoculars will enhance the view.

A fourth bright planet is also in evening view, far to the upper left of the group of three. This is Jupiter, shining high in the southwest. Aside from Venus, it's the brightest point of light in the sky. (In fact, some people may confuse it with Venus until they realize they should be looking much lower and to the right for the Evening Star.)

All these planets appear about the same distance away as you watch them in the deepening dusk, but this is an illusion. Mercury is roughly 90 million miles away (its distance changes during the period illustrated); Venus is about 140 million miles away, and Saturn is 930 million miles -- about 10 times farther than Mercury.

Jupiter is about 500 million miles away. Such big distances are better expressed by how long it takes light to cross them.

Mercury is about 8 light-minutes distant, Venus is about 12 light-minutes away, and Saturn is 85 light-minutes from us. Jupiter is 45 light-minutes distant. By comparison, the stars Pollux and Castor, in the constellation Gemini, are 34 and 52 light-years away, respectively.

NASA's Comet Crash in the Sky

There's another reason to start paying attention to the western dusk. On the night of July 3rd, NASA's Deep Impact probe will slam at 23,000 miles per hour into the icy, mountain-size nucleus of Comet Tempel 1.

Nothing of this event will be visible to the unaided eye (contrary to over-optimistic claims), but at least you can see the place in the sky where it happens.

Find Jupiter again high in the southwest. Off to its left, by somewhat more than the width of your fist at arm's length, is the fainter star Spica, in the constellation Virgo. The impact with the comet will happen a couple of finger-widths above Spica.

The crash is set to happen around 10:52 p.m. Pacific Daylight Time July 3rd (1:52 a.m. Eastern Daylight Time on the morning of July 4th). At that time, Jupiter, Spica, and the comet's position will be in good view from the western United States, especially the Southwest.

Deep Impact's 800-pound projectile should blast a crater anywhere from the size of a large house to the size of a stadium in the comet's 9-by-2.5-mile nucleus, while instruments aboard the main spacecraft watch from a safe distance.

Scientists hope this first-ever comet excavation will provide information about comets' internal composition and structure.

Some of the world's biggest telescopes will also be watching in the following hours, days, and weeks. Countless amateur telescope users will be watching too. But even during and after impact the comet is expected to be faint, and telescope users will need to use a detailed star chart to locate it.

A finder chart showing sufficiently faint stars accompanies this release.

Suitable charts also appear in the June 2005 issue of SKY & TELESCOPE, the July-August 2005 issue of NIGHT SKY, and online at SkyandTelescope.com.

Anyone who's not already familiar with how to use star charts with a telescope will need to follow the beginner's instructions in the online article.

If your evening sky is clear on July 6th or 7th, there's a much easier way to find Comet Tempel 1 with your telescope.

Just center Spica in your lowest-power eyepiece, then let the sky drift by (turn off the scope's tracking motor if ithas one).

Wait exactly 20 minutes, and Comet Tempel 1 should be in the field of view.

Copyright 1995-2005 - SpaceDaily

Explore further: Ceres bright spots sharpen but questions remain

Related Stories

Prospects for Q1 PanSTARRS & G2 MASTER comets

May 08, 2015

Did you catch the performance of Comet C/2014 Q2 Lovejoy earlier this year? Every year provides a few sure bets and surprises when it comes to binocular comets, and while we may still be long overdue for ...

Nanodust particles in the interplanetary medium

Mar 09, 2015

Dust particles smaller than about a wavelength of light are abundant in our solar system, created by collisions between asteroids and from the evaporation of comets. As they scatter sunlight, these particles ...

What makes the solar system interesting to astronomers?

Feb 17, 2015

While most of us are stuck on planet Earth, we're lucky enough to have a fairly transparent atmosphere. This allows us to look up at the sky and observe changes. The ancients noticed planets wandering across ...

Interesting facts about the planets

Feb 17, 2015

While the universe is a big place to study, we shouldn't forget our own backyard. With eight planets and a wealth of smaller worlds to look at, there's more than enough to learn for a few lifetimes!

Why meteors light up the night sky

Feb 09, 2015

Meteors have been seen since people first looked at the night sky. They are comprised of small pieces of debris, typically no larger than a grain of dust or sand, which continually crash into the Earth's ...

Recommended for you

Ceres bright spots sharpen but questions remain

25 minutes ago

The latest views of Ceres' enigmatic white spots are sharper and clearer, but it's obvious that Dawn will have to descend much lower before we'll see crucial details hidden in this overexposed splatter of ...

What are extrasolar planets?

35 minutes ago

For countless generations, human beings have looked out at the night sky and wondered if they were alone in the universe. With the discovery of other planets in our solar system, the true extent of the Milky ...

Rosetta's view of a comet's "great divide"

45 minutes ago

The latest image to be revealed of comet 67P/Churyumov-Gerasimenko comes from October 27, 2014, before the Philae lander even departed for its surface. Above we get a view of a dramatically-shadowed cliff ...

How long will our spacecraft survive?

55 minutes ago

There are many hazards out there, eager to disrupt and dismantle the mighty machines we send out into space. How long can they survive to perform their important missions?

Why roundworms are ideal for space studies

1 hour ago

Humans have long been fascinated by the cosmos. Ancient cave paintings show that we've been thinking about space for much of the history of our species. The popularity of recent sci-fi movies suggest that ...

A curious family of giant exoplanets

1 hour ago

There are 565 exoplanets currently known that are as massive as Jupiter or bigger, about one third of the total known, confirmed exoplanet population. About one quarter of the massive population orbits very ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.