NASA’s UARS (Upper Atmosphere Research Satellite) re-entered the Earth’s atmosphere last night between 8:20pm and 10:10pm Pacific Time. At the time of this writing (2am? Oops), the exact time and location of re-entry are unknown, though NASA says it was over the Pacific Ocean. There were some unconfirmed reports that it fell over northern Canada.

More Interesting

What I found most fascinating is why they were unable to predict the exact decay of this orbit: solar radiation. Solar radiation (think heat from the Sun, though it would be more precise to say photons from the Sun) heats up the Earth’s atmosphere, specifically the upper atmosphere where satellites in Low-Earth Orbit can be as their orbits decay. This heating makes that part of the Earth’s atmosphere both larger and less dense. NASA likens this to a marshmallow being toasted over a campfire. So now your satellite is travelling through a different density of atmosphere, where it will experience more or less drag depending on what exactly is happening between the Sun and the Earth’s upper atmosphere. Complicated, especially if you can’t see that density changing.

Want More?

NASA’s UARS site with the most recent official updates

More about solar radiation and satellite orbit decay

Twitter and Spaceflight Now have more information, but not official information

~ A l i c e !

Time for the seasonal sunset watch. I hope you’re excited, we had such fun at the last-minute stargazing last week.

• When: September 23, 2011 at 6:50pm (so come at 6:30pm)
• Actual sunset is supposed to be at 7:05, but at the summer solstice we noticed that the Sun set about 10 minutes earlier than the USNO says it does, so I’ve moved the time of our sunset watch up so we don’t miss it. I added another 5 minutes for the tall trees of Lincoln Park blocking our view.
• Where: Solstice Park – all the way up the hill from the tennis courts (or, if you’re not in Seattle, wherever you have a view of the western horizon!)
• Who: Everyone welcome, as usual.

Sunset on June 21, 2011 at 9pm Credit: Jason Gift Enevoldsen

Today is a great day to announce the Autumn Equinox Sunset Watch because today is the Zhōngqiū Jié, 中秋節, or the Mid-Autumn Festival! Legend has it that once upon a time there were ten Suns, but Hou Yi was very strong and shot nine of them out of the sky. He was rewarded with the Elixir of Life – which would make him immortal. Unfortunately, he was so full of himself that he became a lazy tyrant, and his wife Cháng’é didn’t think it was a good idea for him to live forever, so she took the Elixir instead and began to float away. If you want to find out what happened to Cháng’é, you’ll have to come to the Sunset Watch where I will tell the whole story!

Today would be a great day to visit the Seattle Chinese Garden, here in West Seattle!

Come watch the autumn equinox sunset at Solstice Park in West Seattle on Friday the 23rd. We’ll see if the sunset lines up with the placed marker (it did for summer, but will it for fall?). I’ll be there even if it is cloudy because sometimes the Sun peeks through just as it begins to set, but if it is driving rain I’m staying home.

If you’re interested – here’s the timing of various celestial events on Saturday from Seattle, courtesy of the U.S. Naval Observatory Astronomical Applications Department:

Sun and Moon Data for One Day
The following information is provided for Seattle, King County, Washington (longitude W122.3, latitude N47.6):

Friday 23 September 2011 Pacific Daylight Time

SUN
Begin civil twilight 6:26 a.m.
Sunrise 6:57 a.m.
Sun transit 1:02 p.m.
Sunset 7:05 p.m.
End civil twilight 7:36 p.m.

MOON
Moonset 4:22 p.m. on preceding day
Moonrise 2:13 a.m.
Moon transit 9:40 a.m.
Moonset 4:53 p.m.
Moonrise 3:30 a.m. on following day

Phase of the Moon on 23 September: waning crescent with 18% of the Moon’s visible disk illuminated.

Last quarter Moon on 20 September 2011 at 6:39 a.m. Pacific Daylight Time.

This event is my part of the NASA’s Solar System Ambassadors program, and thanks to West Seattle Blog for publicizing the last few!

Everyone is welcome, see you there!

Resources on Zhōngqiū Jié: Childbook, Chinatown Online, and Wikipedia.

~ A l i c e !

The weather looks reasonable, so let’s try for some guerrilla stargazing at Solstice park tonight.

• When:  TODAY! Sept 4, 2011 at 9pm
• Where: Solstice Park – all the way up the hill from the tennis courts (or, if you’re not in Seattle, wherever you have a view of the western horizon!)
• Who: Everyone welcome, as usual.

Come stargaze with us at Solstice park tonight. We’ll be looking for Comet Garradd and Supernova PTF11kly in Galaxy M101 through telescopes.

Here’s approximately what those might look like with out telescopes. They will not be visible to the naked eye.

Comet Garradd

Supernova PTF11kly in Galaxy M101

If you’re interested – here’s the timing of various celestial events for today from Seattle, courtesy of the U.S. Naval Observatory Astronomical Applications Department:

Sun and Moon Data for One Day

The following information is provided for Seattle, King County, Washington (longitude W122.3, latitude N47.6):

        Sunday
        4 September 2011      Pacific Daylight Time          

                         SUN
        Begin civil twilight       6:00 a.m.
        Sunrise                    6:32 a.m.
        Sun transit                1:08 p.m.
        Sunset                     7:44 p.m.
        End civil twilight         8:16 p.m.
        End astronomical twilight  9:34 p.m.

                         MOON
        Moonset                   10:40 p.m. on preceding day
        Moonrise                   2:58 p.m.
        Moon transit               7:16 p.m.
        Moonset                   11:34 p.m.
        Moonrise                   3:53 p.m. on following day

This event is my part of the NASA’s Solar System Ambassadors program, and thanks toWest Seattle Blog for publicizing the last few!

Everyone is welcome, see you there!

~ A l i c e !

Are you reading this in a pre-coffee haze? Click on this link:

Alice’s Live Shuttle Launch Comments

Here’s what’s happening, if you’re not in the haze of the uncaffinated early morning:

Provided the weather in Florida holds out, I’ll be commenting live about the final shuttle launch tomorrow morning around 7:30/7:45am Seattle time (PDT). I am still here in Seattle, but since the launch is scheduled for 8:26am our time and Pacific Science Center won’t be open yet, I thought we could chat online.

Joining me will be Sarah Culp, planetarium intern, and Ballard High School graduate (class of ’11!). She and her class sent an experiment with e-coli up on the previous shuttle mission. We’ll probably chat about that as well.

If you want to join us, we’ll be on Twitter (AlicesAstroInfo) using the hashtag #PacSciLive, as well as the official launch hashtag #STS135. You don’t have to sign in to Twitter to read the comments, but you do if you want to talk back. You can also leave comments below, on my Facebook page or e-mail me. I’ll be watching all those for questions from you.

Cross your fingers for good weather in Florida!

~ A l i c e !

There is an eclipse on Wednesday June 15, being touted as a rare central lunar eclipse. It is – but it is also very similar to the eclipse we had in December. The “rare” part is that it has a whopping 1 hour and 40 minutes of totality (that’s when the whole face of the moon is darkened by the Earth’s shadow). The eclipse we saw in December had 1 hour and 12 minutes of totality.

Unfortunately, the eclipse is not visible here at all – it peaks at 2:15 in the afternoon, and on Wednesday the Moon will not be visible from Seattle at that time. There is an observatory in Israel that will hook up a live feed to the internet if you want to watch on the web.

Lunar Eclipse 12/21/2010 in Seattle ©2010 Jason Gift Enevoldsen

Most lunar eclipses I’ve seen have had much shorter periods of totality – though it looks like more than an hour is not uncommon. Between the year 2000 and the year 2020, periods of totality last as little as 5 minutes and up to an hour and a half. Usually they seem to be about an hour.

Want More?

http://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2011Jun15T.pdf
http://www.mreclipse.com/Special/LEnext.html

~ A l i c e !

I’m back! Time for the seasonal sunset watch!

• When: Tuesday, June 21, 2011 at 9:11pm (so come at 8:45pm)
• Where: Solstice Park – all the way up the hill from the tennis courts (or, if you’re not in Seattle, wherever you have a view of the western horizon!)
• Who: Everyone welcome, as usual.

Sunset on June 21, 2011 at 9pm Credit: Jason Gift Enevoldsen

Come watch the summer solstice sunset at Solstice Park in West Seattle on Tuesday the 21st. We’ll see if the sunset lines up with the placed marker. I’ll be there even if it is cloudy because sometimes the Sun peeks through just as it begins to set, but if it is driving rain I’m staying home.

If you’re interested – here’s the timing of various celestial events on Saturday from Seattle, courtesy of the U.S. Naval Observatory Astronomical Applications Department:

Sun and Moon Data for One Day

The following information is provided for Seattle, King County, Washington (longitude W122.3, latitude N47.6):

Tuesday  21 June 2011          Pacific Daylight Time

SUN
Begin civil twilight       4:31 a.m.
Sunrise                    5:11 a.m.
Sun transit                1:11 p.m.
Sunset                     9:11 p.m.
End civil twilight         9:52 p.m.

MOON
Moonrise                  11:56 p.m. on preceding day
Moon transit               5:43 a.m.
Moonset                   11:41 a.m.
Moonrise                  12:16 a.m. on following day

This event is my part of the NASA’s Solar System Ambassadors program, and thanks to West Seattle Blog for publicizing the last few!

Everyone is welcome, see you there!

~ A l i c e !

WARNING: THIS POST IS OVERWHELMING. There is too much information in one place, but I promise there are fun and interesting gems hidden within. It is meant as a reference, and a starting point for discussion of each of these topics.

There are a few numbers and references I am often asked for, especially at the West Seattle solstice and equinox sunset watches. I thought I’d collect these things in one place for “easy” reference.

Strict Definitions (from the USNO)

Equinox – The time at which the Sun passes through one of the two points on the celestial sphere where the celestial equator and the ecliptic intersect. (Yup, pretty technical – the non-technical version is “when the Earth’s axis is pointed neither towards nor away from the Sun.”)

Solstice – The time at which the Sun is at either of the two points on the ecliptic at which the longitude of the Sun is 90° or 270° (halfway between the equinoxes). The non-technical version is “when the Earth’s axis is pointed exactly towards or exactly away from the Sun.”

Horizon – Your eye is considered to be the surface of the Earth, so the horizon is the line exactly straight out from your eyes, or exactly 90 degrees down from the point directly above your head.

Sunrise and Sunset – When “the upper edge of the disk of the Sun is on the horizon, considered unobstructed” (calculations assume a flat horizon). To calculate this exactly, one assumes that this occurs when the Sun is 90.8333°  from the zenith (0.8333° below the horizon as defined above). The extra 0.8333° take into account both the radius of the Sun’s disk and an average amount of refraction due to the atmosphere.

Two more notes on rise and set times. First, atmospheric refraction is very important, and small changes in the quality of the atmosphere (humidity, cloud layers, etc) can change apparent rise and set times by at least a minute. Also “at high latitudes … small variations in atmospheric refraction can change the time of rise or set by many minutes, since the Sun and Moon intersect the horizon at a very shallow angle.”

Twilight – there are a few different types of twilight.

Civil Twilight – When the center of the Sun is 6° below the horizon. You can still see during civil twilight, and may not need to turn on outdoor lights. The brightest stars become visible at the beginning or end of civil twilight (“Star light, star bright, first star I see tonight …” you’re still in civil twilight).

Nautical Twilight – When the center of the Sun is 12° below the horizon. You can see objects indistinctly, but you need to turn on lights to do anything detailed.

Astronomical Twilight – When the center of the Sun is 18° below the horizon. The Sun “does not contribute to sky illumination.” It’s dark after astronomical twilight ends.

Change in Amount of Daylight

In Seattle our longest day is about 15 hours 30 minutes, with the shortest night being about 8 hours and 30 minutes. Similarly, our shortest day is about 8 hours 45 minutes, with the longest night being about 15 hours and 15 minutes.

The change in amount of daylight per day varies through the seasons. In Seattle,

• Just before the spring equinox the days are lengthening by about 4 minutes.
• Just before the summer solstice the days are lengthening by significantly less than a minute.
• Just before the fall equinox the days are shortening by about 4 minutes.
• Just before the winter solstice the days are shortening by significantly less than a minute.

Calculate the exact amount of daylight for Seattle or your own location.

Equal Day and Equal Night on the Equinox?

The day and night are not quite equal on the equinox. This is partially due to atmospheric effects and terrain (like mountains or hills), and partially due to your latitude.

At different latitudes the Sun sets at different angles – for instance, at the North Pole it is skimming the horizon, but at the equator it sets almost vertical. Most of us are somewhere in between. It takes longer for the Sun to set when it sets at a shallow angle than at a steep one, and since sunset is defined as when the top edge of the Sun is on the horizon, rather than the center, this gives most of us and uneven day and night on the equinoxes.

A much longer explanation.

Sun Angles for Seattle

• Angle of sunrise and sunset for Seattle is always: 43°
• Summer solstice maximum height of the Sun (highest the Sun ever gets in Seattle): 66°S
• Equinox maximum height of the Sun in Seattle: 43°S
• Winter solstice maximum height of the Sun (lowest “high point” of the Sun’s path through the year): 19°S

Earliest Sunrise/Latest Sunset
Latest Sunrise/Earliest Sunset

See my Dark Days of Winter post. Or the one by the USNO.

Dates and Times (Seattle Local)

Daylight Savings Time (USA, as of 2011)

• Second Sunday in March – spring forward – daylight time begins, 2:00am becomes 3:00am. Lose an hour.
  • Pacific Daylight Time is 7 hours earlier than Universal Time (UTC).
• First Sunday in November – fall backward – standard time begins, 2:00am becomes 1:00am. Gain an hour.
  • Pacific Standard Time is 8 hours earlier than Universal Time (UTC).

Slippage – Are the Equinoxes Moving?

Since the introduction of the Gregorian Calendar with its crazy leap days every 4 years (except for every 100 years (except for every 400 years)) … we’ve made it so the date we call the spring equinox (March 21) will take 3300 years to get one full day out of sync with the time the Earth is at the actual position of the spring equinox.

This could be interpreted to mean the vernal equinox is slipping by one minute every 2-3 years on average, but you will notice hours more slippage year to year, because leap days correct for the length of the year over a 400-year cycle, not continuously. Between leap years we accumulate “error.” This error is corrected all at once by a leap day, or lack of a leap day.

Example (ignore if you don’t find numbers helpful): each year the equinox is about 5 hours and 45 minute later, but on a leap year it is both 5 hours 45 minutes later AND one day earlier (or simply approximately 18 hours and 15 minutes earlier if you prefer). This in turn accumulates a slip of about 45 minutes every 4 years, which is mostly corrected for only when we skip a leap day on the 100th year.

(Are you math-y? This may help you: We correct for the error discretely, rather than continuously.)

Too much? Think of it as a ratchet that resets every 4, 100, and 400 years to almost the exact beginning position. Each ratchet motion is noticeable, but after you’ve reset it’s pretty unnoticeable.

Movement of Perihelion and Aphelion

You’d think perihelion (Earth’s point nearest the Sun) and aphelion (Earth’s point farthest from the Sun) would be as set in place in our orbit as the equinoxes and the solstices. Not so. Since the Moon and Earth orbit a common center of gravity, the Moon’s orbit causes the Earth to be slightly closer or farther from the Sun at any given time. Since the Moon isn’t in the exact same point in its orbit each year when we reach the approximate location of perihelion or aphelion, this disturbance in our orbit causes a slight change in that location year to year.

Links I Use in Planning Seasonal Events

Dates of Earth’s Primary Seasons – This is where I get the exact day and time of each solstice and equinox. This is in Universal Time (UTC) and must be converted to your local time.

Time Zone Converter – This is where I go to convert the time from the link above (solstice or equinox) from Universal Time (UTC) into Pacific Time. I use “USA – Washington – Seattle” rather than Pacific Standard Time or Pacific Daylight Time so I don’t have to remember when we switch off of Daylight Savings. Which, by the way, I look up here if I need to.

• PST is 8 hours earlier than UTC.
• PDT is 7 hours earlier than UTC.

Complete Sun and Moon Data for One Day – This is where I get the time of the Seattle sunset for each sunset watch.

Definitions of Rise, Set, and Twilight

~ A l i c e !

Yup! It’s that time again. Time for the quarter-annual sunset watch … only this time I’ll be 8.25 months pregnant when we meet!

• When: Sunday, March 20, 2011 at 7:22pm (so come at 7:00pm)
• Where: Solstice Park – all the way up the hill from the tennis courts (or, if you’re not in Seattle, wherever you have a view of the western horizon!)
• Who: Everyone welcome, as usual.

Sunset on June 11, 2009 Credit: Jason Gift Enevoldsen

Come watch the spring equinox sunset at Solstice Park in West Seattle on Sunday the 20th. We’ll see if the sunset lines up with the placed marker. I’ll be there even if it is cloudy because sometimes the Sun peeks through just as it begins to set, but if it is driving rain or sleet I’m staying home with a cup of tea.

If you’re interested – here’s the timing of various celestial events on Saturday from Seattle, courtesy of the U.S. Naval Observatory Astronomical Applications Department:

Sun and Moon Data for One Day

The following information is provided for Seattle, King County, Washington (longitude W122.3, latitude N47.6):

Sunday   20 March 2011         Pacific Daylight Time

SUN
Begin civil twilight       6:42 a.m.
Sunrise                    7:13 a.m.
Sun transit                1:17 p.m.
Sunset                     7:22 p.m.
End civil twilight         7:53 p.m.

MOON
Moonrise                   7:57 p.m. on preceding day
Moon transit               1:41 a.m.
Moonset                    7:12 a.m.
Moonrise                   9:21 p.m.
Moonset                    7:41 a.m. on following day

Phase of the Moon on 20 March: waning gibbous with 98% of the Moon’s visible disk illuminated.

Full Moon on 19 March 2011 at 11:11 a.m. Pacific Daylight Time.

This event is my part of the NASA’s Solar System Ambassadors program, and thanks to West Seattle Blog for publicizing the last few!

Everyone is welcome, see you there!

~ A l i c e !

Late last night NASA’s probe Stardust-NExT had a close encounter with Comet Tempel 1, and took 70-some-odd pictures as it went by. Due to bandwidth as well as the limited speed of light, the images arrived at Earth around 12:45am Pacific Time – and then had to go through basic processing by the Science team.

First picture to come back.

There will be more, better, prettier images later on this morning. I’ll add to this post sometime after I wake up in the Seattle morning to make sure you see those. Meanwhile here is where they reside.

A closeup of Comet Tempel 1 by Stardust courtesy NASA/JPL-Caltech/Cornell

Although there are many things to observe at Comet Tempel 1, the part I am most interested in is the before-and-after of the comet’s trip around the Sun.  We already have some data of before and after the Deep Impact crash, but what changes about a comet when it passes close to our favorite star? Deep Impact’s observations are as Tempel 1 approaches the Sun, and Stardust-NExT saw it on the other side, after it passed by.We know comets lose a good amount of material – so what will we see when the pictures come back? How different will Tempel 1 look?

Remember When?

Comet Tempel 1 as seen by Deep Impact - Courtesy NASA

Tempel 1 – Deep Impact

Deep Impact Crash video

Back in July 2005 NASA’s mission Deep Impact sent an impacting probe to crash into Comet Tempel 1. According to JPL’s recent news release summing up the mission:

Scientists were surprised the cloud was composed of a fine, powdery material, not the expected water, ice, and dirt. The spacecraft did find the first evidence of surface ice on the surface of a comet instead of just inside a comet.

Stardust and Stardust NExT

A Heart-Shaped particle collected by Stardust from Comet Wild 2 - Courtesy Stardust program

Stardust was masterminded by one of our own local astronomy celebrities here in Seattle, Dr. Don Brownlee. Don’s a good speaker especially about Stardust, so if you have a chance to hear a lecture by him I’d go to it.

Stardust’s original mission was to collect particles from a the tail of Comet Wild 2 in what was effectively a tennis racket filled with aerogel. They did this in January of 2004. On the second side of the tennis racket collector it gathered a few particles of interstellar dust.

From a press release in 2007 about the findings in the comet tail particles:

They do contain some stardust grains from other stars but the majority of solids are solar system materials that appear to have formed over a very broad range of solar distances and perhaps over an extended time range. Comet Wild 2 is a collection of materials that probably came from all regions of the young solar system and thus it has turned out to be wonderful “time capsule”.

Comet Comparisons

Go check out Emily’s post – she made this picture.

Comets Compared by Emily Lakdawalla

Want More?

Press Release from Stardust-NExT about the encounter with Tempel 1

Stardust-NExT

Deep Impact

Stardust Heart-Shaped Particle

~ A l i c e !

This is a week of sad anniversaries.

• 1/27/1967 – Apollo 1 lost (Crew of 3 – Gus Grissom, Ed White, Roger Chaffee)
• 1/28/1986 – Challenger lost (Crew of 7 – Dick Scobee, Michael Smith, Judith Resnik, Ron McNair, Ellison Onizuka, Gregory Jarvis, Christa McAuliffe). Reagan postponed his State of the Union address in 1986 to speak in memory of the crew, dubbed the “Challenger 7.”
• 2/1/2003 – Columbia lost (Crew of 7 – Rick Husband, William McCool, Michael Anderson, David Brown, Kalpana Chawla, Laurel Blair Salton Clark, Ilan Ramon). A range of hills on Mars near Gusev Crater is named after the crew, and was later explored by the rover Spirit.
• The other three space missions which ended in loss of life were in April 1967 (Soyuz 1 – Vladimir Komarov), June 1969 (Soyuz 11 – Viktor Patsayev, Georgi Dobrovolsky, and Vladislav Volkov), and November 1967 (the X-15 – Michael Adams).

Diagram of “Significant Incidents”

I know this diagram is complex, but start with the bright yellow boxes – and go from there, although depressing there’s quite a lot if intriguing information packed in here.

I visited the Astronaut Memorial at Kennedy Space Center two years ago, and I hope they never have to add another name to it.

Want More?

If the links to the image don’t work – use this one. Or the source.

~ A l i c e !