Category: Astronomy

Exploring the cosmos

Earth and The Milky Way Just Got a Few Trillion New Neighbors

W. M. Keck Observatory press release…

Do you know where you live? You probably know your street address and the name of your town, state, and country. But what about your cosmic address — your location among the stars? Thanks to efforts by some astronomers in Hawaii, you can now tell people you live in Laniakea.

Scientists have known for decades that our solar system rests on an outer arm of the Milky Way galaxy. In turn, galaxies are not sprinkled randomly throughout the cosmos; they cluster into groups, which themselves are part of larger groups.

Laniakea Supercluster
Two views of the Laniakea Supercluster. The outer surface shows the region dominated by Laniakea’s gravity. Credit CEA/SACLAY
What has been known is our Milky Way is part of the Local Group, a collection of galaxies some 10 million light-years across. Now, a team of scientists led by University of Hawaii at Manoa astronomer R. Brent Tully have mapped the boundaries of a “supercluster” of galaxies stretching 500 *million* light-years through space. They named the supercluster “Laniakea,” a Hawaiian word meaning “immense heaven.” The name was suggested by Kapiolani Community College linguist Nawa’a Napoleon as a tribute to the Polynesian sailors who crossed the Pacific, navigating by the stars.

Tully’s team determined Laniakea’s contours using a method similar to the way geographers would map watersheds on Earth. In an article published in the September 2014 issue of Nature, Tully and his co-authors Hélène Courtois, Yehuda Hoffman, and Daniel Pomarède describe how they began by measuring the distance from Earth to more than eight thousand galaxies and observing the galaxies’ movement. From those measurements, they calculated each galaxy’s “peculiar velocity,” or the difference between its observed velocity and the rate at which all galaxies are receding from each other (called the “cosmic expansion”).

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Autumnal Equinox

Fall equinox occurs today at 16:30HST. Today there will be little difference between the length of the night compared to number of daylight hours. This is the first day of fall as marked by many cultures in the northern hemisphere.

This year many calendars will mark September 23rd as the beginning of fall, and so it is for much of the world. Here in Hawai’i the equinox actually occurs on the 22nd when considering the time zone differences.

2014 Solstices and Equinoxes
  UT HST
Perihelion Jan 4 05:59UT Jan 3 19:59HST
Vernal Equinox Mar 20 16:57UT Mar 20 06:57HST
Summer Solstice Jun 21 10:52UT Jun 21 00:52HST
Apehelion Jul 3 22:59UT Jul 3 12:59HST
Autumnal Equinox Sep 23 02:30UT Sep 22 16:30HST
Winter Solstice Dec 21 23:03UT Dec 21 13:03HST
 
Source: NASA Sky Calendar

 

Mercury at Maximum Elongation

Today Mercury reaches maximum elongation, the furthest point it will reach from the Sun in our sky and the highest it will be above the sunset for this evening apparition. The planet is easily visible as a bright, starlike object about 26° above the setting Sun as twilight begins. Over the next couple weeks Mercury will slide back into the sunset, heading for inferior conjunction on October 16th.

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The Moon and Jupiter

Tomorrow morning the Moon and Jupiter will be close. The Moon will rise first, followed by Jupiter at 03:06 to be almost 40° above the eastern horizon at sunrise. The Moon will be about 18% illuminated and about 8° above a bright Jupiter. The next day the Moon will have moved to the other side of Jupiter but will be even closer, about 7° separation.

Working Late Again

When most folks work late at the office it is a boring evening at a desk staring at a computer. I may have stared at a computer a bit, but it was hardly a boring evening.

CloudCam Image
A focusing test shot from the Keck CloudCam
The task that had me staying late was to focus the new cloud camera. To accomplish this task I needed a dark sky and stars. The plan is the same as I have used before, work the day and then stay into the evening.

Waiting for darkness had it’s advantages, an opportunity to do a little photography. In addition to the usual tool bag and lunch I took my camera gear with me.

With Sniffen on the roof while I watched the frames on the computer, I called the corrections up to him on the radio. It is tricky work to focus a fast lens, made worse by the need to do it remotely. We had to wait for each 30 second exposure, painfully slow. I hesitated to ask Sniffen to sit much longer out in the cold, but he was game and ready to assist. His tiny adjustments were deftly made, I watched as the lens moved through focus.

VLBA & Milky Way
The summer Milky Way soars over the VLBA antenna atop Mauna Kea
The focus is not as good as I would like to see, I suspect that the Sigma 18mm f/1.8 lens leaves a little to be desired when used wide open. Perhaps one of the Rokinon lenses would work better. Or maybe I just need to step the lens down a stop or two.

After leaving Keck I took my time wandering down the mountain. I stopped at IRTF for a set of panorama shots. One of the first things I noted was the lack of airglow. Last time I shot from the summit the airglow was intense. Despite using the same camera and lens, with the same settings, the bright red glow was missing. Only a pale green near the horizon to be seen in the shots.

On a whim, I drove out to the VLBA antenna for a set of shots. This radio telescope was something different than the usual telescope shots I take. I walked around the dish until I could position the summer Milky Way beside the antenna. As the VLBA is a radio telescope there was no issue in using a little light from my flashlight to paint the dish and illuminate it for the photo.

I arrived home just before midnight, tired from a full day on the summit. The photos will wait for another day for processing.