Astronomy Picture of the Day 9-15-02

NASA ^ | 9-15-02 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2002 September 15

Zodiacal Light and the False Dawn
Credit: Night Sky Live Project, CONCAM, NSF

Explanation: An unusual triangle of light will be particularly bright near the eastern horizon before sunrise during the next two months for observers in Earth's northern hemisphere. Once considered a false dawn, this triangle of light is actually Zodiacal Light, light reflected from interplanetary dust particles. The triangle is clearly visible on the left of the above frame taken from Mauna Kea in Hawaii on September 8 by one of the developing global network of fisheye nighttime web cameras, called CONCAMs, of the Night Sky Live Project. Zodiacal dust orbits the Sun predominantly in the same plane as the planets: the ecliptic. Zodiacal light is so bright this time of year because the dust band is oriented nearly vertical at sunrise, so that the thick air near the horizon does not block out relatively bright reflecting dust. Zodiacal light is also bright for people in Earth's northern hemisphere in March and April just after sunset.

[petuniasevan]

Astronomy Fun Fact:

It's called "Zodiacal light" for its appearance in the same plane ("Ecliptic") as the constellations of the zodiac. They in turn are significant for the fact that the planets, moon and sun seem to pass through them as seen from earth. This is the orbital plane of the planets. Dust particles between the sun and Jupiter reflect sunlight; it's easiest to see when the orbital plane is vertical to our point of view.

Ever seen the zodiacal light? Try it out this month! You'll need to find a DARK location. No lights AT ALL to the east. The moon would wash it out; try for a phase when it'll already be set. Be ready for the light at least 1 hour before morning twilight is to begin. Patience and the realization that this light is diffuse and subtle are a great help.

We are 2 days past first quarter moon. In 6 days' time the moon will be setting with the sunrise, so get that look-see in before a week is out. After full moon the mornings will be a washout until about the 4th of October. Then you can look for the Zodiacal light again in early October (though it's not as easy to find).

Advanced extra-credit work for you astrotrivia hounds: What is the Gegenschein? How is it related to today's topic?
Try to observe it. (Hint: November is the best time).

[petuniasevan]

[sleavelessinseattle]

I didn't check, but I seem to remember that the gegenshein is a triagle of light visible at midnight that is caused by dust particles sparkling and is directly overhead??? It was on Star hustler a couple days back.

[sleavelessinseattle]

triagle=triangle...too much cold meds, there...so solly.

[petuniasevan]

DING DING DING! You got it! Now the tough part: Try to observe it!
It's much harder to find that the Zodiacal light!

Eww...you watch DORKheimer's show? I know it's educational and all, but he's so creepy...

[sleavelessinseattle]

Yeah You gotta wonder if he isn't the recipient of the most amazing Witness Protection Plan job reassignment in History...

[2Trievers]

"DING DING DING! You got it!"

This is NO FAIR 'tunia. Sleavester is the kid I remember who always had his hand up first in class with the answer, while the rest of us were still wondering what class we were in, never mind what chapter or page the professor was on. NO FAIR!

Howz your cold? Whoever invented Nyquil should get the Nobel ... Sleavester gets a gold star and another dose brilliance! &;-)

[BossyRoofer]

Great picture, will get up early for a look see! Good job APOD!

[BradyLS]

"GREETING! GREETINGS! FELLOW STAR GAZERS!...."

He might not be so bad if Tomita's whistly-version of "Claire de Lune" (if I have that right) weren't playing in the background. That's, like, music for a haunted theater. But, yah, he seems to be enjoying himself a little too much.

But he does clue you in on some interesting home atronomy stuff-- if you can just get up that early!

It's been years since I've seen this guy on TV. He's still doing "The Star Hustler?" (Why on earth did he call it that?)

[mikrofon]

Neat APOD item ... thanks!

It's interesting that, at this time of year when the steep angle of the ecliptic to the morning horizon allows for the best viewing of the Zodiacal Lights, conversely the shallow angle of the ecliptic at full moonrise gives us the phenomenon of the Harvest Moon -- Nature's "night-light" rising soon each evening around the full phase in early autumn would provide additional time for gathering in the crops after sunset.

[RightWhale]

Ever seen the zodiacal light?

Never. And I expect I never will because of light pollution. The sky needs to be dark, totally dark, which is not possible in most of the continental United States, including Alaska.

[petuniasevan]

That's too bad. It's true; most people never will see it.

I did on a pre-dawn early October morning in 1975 while camping in the Sierra Nevada mountains (on the eastern side) between Bishop and Mammoth Mountain. Elevation was 9000 feet; temperature was way too low for my liking.

I've never since seen such a dark sky; it looked like black velvet strewn with diamond dust an inch in front of me.

The zodiacal light really stood out, as there is nothing but the White Mountains and the Nevada desert to the east there.

[BradyLS]

About 15 years ago, I saw the Milky Way through night vision goggles on a clear night in the desert around Fort Irwin, California. It was dazzling enough without it, but seeing the light from those stars magnified against the green field created by the goggles was amazing. Sunlight ruins them by burning out the receptors.