ÿþ<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <meta http-equiv="Content-Type" content="text/html;charset=utf-8" > <title>philatelicgems.com : Find Your Local Sidereal Time (LST)</title> <meta NAME="Author" CONTENT="sandra@philatelicgems.com"> <META NAME="Keywords" CONTENT="Sandra Rout,astronomy,LST,GST,local sidereal time,Greenwich sidereal time,Universal Time,Greenwich Mean Time,Find Your Local Sidereal Time,Find Your LST"> <meta NAME="Description" CONTENT="philatelicgems.com : Find Your Local Sidereal Time (LST)."> <script language="JavaScript" type="text/JavaScript"> var name = "sandra"; var domain = "philatelicgems.com"; var item = "Find LST"; if (screen.width < 750) document.write('<link rel="stylesheet" type="text/css" href="http://www.philatelicgems.com/styles/S640A.css">'); if (screen.width > 640 && screen.width < 950) document.write('<link rel="stylesheet" type="text/css" href="http://www.philatelicgems.com/styles/S800A.css">'); if (screen.width > 800 && screen.width < 1100) document.write('<link rel="stylesheet" type="text/css" href="http://www.philatelicgems.com/styles/S1024A.css">'); if (screen.width > 1024 && screen.width < 1250) document.write('<link rel="stylesheet" type="text/css" href="http://www.philatelicgems.com/styles/S1152A.css">'); if (screen.width > 1200) document.write('<link rel="stylesheet" type="text/css" href="http://www.philatelicgems.com/styles/S1280A.css">'); </script> <script language="JavaScript" type="text/JavaScript" src="http://www.philatelicgems.com/astronomy/lstCities.js"> </script> <script language="JavaScript" type="text/JavaScript" src="http://www.philatelicgems.com/astronomy/jdays.js"> </script> <script language="JavaScript" type="text/JavaScript" src="http://www.philatelicgems.com/astronomy/calcGST.js"> </script> <table width="100%" border="0" cellpadding="0" cellspacing="0"> <tr bgcolor="#0032A1"> <td width="131" height="100" align="center"> <table width="121" border="0" cellpadding="0" cellspacing="0" bgcolor="#0032A1"> <tr> <td align="center"><IMG SRC="http://www.philatelicgems.com/art/Z1.jpg" WIDTH="203" HEIGHT="133" BORDER="0" ALT="Sandra Rout"></td> </tr> </table> </td> <td height="140" align="center"><br><IMG SRC="http://www.philatelicgems.com/art/Z2.jpg" WIDTH="603" HEIGHT="79" BORDER="0" ALT="Sandra Rout"><br><h3>Find Your Local Sidereal Time</h3></td> <td width="30" height="100">&nbsp;</td> </tr> <tr bgcolor="#000033"> <td></td><td></td><td></td> </tr> <tr> <td width="181" bgcolor="#990000" valign="top" class="leftside"> <p class="class1"><br>MENU:<br><br><span class="class1"><a href="http://www.philatelicgems.com/">Home Page</a><br>******<br><a href="http://www.philatelicgems.com/contest.html">Free Contest</a><br>******<br><a href="http://www.philatelicgems.com/catalog/">Fine Stamps</a><br>******<br><a href="http://www.philatelicgems.com/RSA1977.html">RSA 1977 Definitives</a><br>******<br><a href="http://www.philatelicgems.com/protea-controls.html">Protea Controls</a><br>******<br><a href="http://www.philatelicgems.com/siteterms.html">Terms/Conditions</a><br>******<br><a href="http://www.philatelicgems.com/sitemap.html">Sitemap</a><br>******<br><a href="http://www.philatelicgems.com/astronomy/">Astronomy Menu</a></span></td> <td valign="top" class="text"> <table width="100%" border="0" cellspacing="0" cellpadding="20"> <tr> <td class="text"> <p> Local civil time in any part of the world depends upon Universal Time (also known as Greenwich Mean Time), which in turn is dependent upon the motion of the Sun. As a rule of thumb, we can say that one solar day is the time taken between two successive passages of the Sun across the meridian at any given spot in the world. As astronomers, whether amateur or professional, we are interested in the motion of the stars, and just as a solar clock measures the two passages of the Sun across a meridian, we need a clock that measures two successive passages of any given star over any given meridian. Such a clock is called a sidereal clock, and it follows that the time it measures is known as sidereal time. <p> Astronomers need to use a clock that will allow exactly 24 hours to pass when a star is observed at the same position in the sky on two successive days. We call this a <I>sidereal clock</I>; its time is therefore called sidereal time. This is not the same as solar time (Universal Time is an example of solar time) because during the course of a solar day the Earth moves almost a full degree in its orbit around the Sun. There are about 365¼ solar days in a year; during this period, the Earth makes about 366¼ revolutions around its own axis. It follows that there are 366¼ days in a sidereal year, and this means that a sidereal day is slightly shorter than a solar day -- 23 hours and 56 minutes for the sidereal day, 24 hours for the solar day. Universal time and Greenwich sidereal time agree at exactly one instant each year, at the autumnal equinox on or about September 22. The difference in sidereal and solar times grows so that half a year later the difference is exactly 12 hours. <p> The formal definition of sidereal time is that it is the hour-angle of the vernal equinox. What does that mean? Celestial longitude has to have a starting point in the heavens to measure from, just as terrestrial longitude is measured from a fixed point on at the Greenwich meridian. This fixed point in the sky is known as the first point of Aries; it was not, of course, chosen randomly. It is the point in the sky where the Sun crosses the celestial equator each spring; this event occurs around March 21 each year, and is known as the vernal equinox. If we projected the Earth's equator into the heavens, the vernal equinox lies where that celestial equator would intersect with Earth's orbit around the Sun. <p> In practical terms, you need to know your local sidereal time (LST) to better view the stars. The stars are (usually) mapped using equatorial coordinates, which are expressed as right ascension and declination. Right ascension can be thought of as "how far around", in other words as celestial longitude. Declination is how far "up or down", or the equivalent of celestial latitude. Sidereal time and right ascension work together, because if a star has a right ascension of say 17 hours and 42 minutes, that star is best observed when your LST is 17 hours and 42 minutes. That big old star in Orion which we call Betelgeuse has a right ascension of 5 hours 55 minutes, so the best time to observe Betelgeuse is when your LST is about 6 hours and it is also dark enough to see the stars (it would not help much if, for the given example, your LST was 6:00 but the civil time was noon). <p> You can easily find your current (or any other) LST by making a few quick selections below. <p> <font size="+1""><B>CALCULATE YOUR LOCAL SIDEREAL TIME NOW</B></font> <!-- First we have to discover the longitude of the user --> <FORM name="getc" action="" method="get"> <div id='dPickCity'> <p>Select a location close to you:<br> <SELECT NAME="city" size="1"> <OPTION value="Amman">'Ammn (Amman) <OPTION value="Abidjan">Abidjan <OPTION value="Accra">Accra <OPTION value="Addis Abeba">Adis Abeba (Addis Abeba) <OPTION value="Ahmadabad">Ahmadbd (Ahmadabad, India) <OPTION value="Alexandria">Al-Iskandar+yah (Alexandria) <OPTION value="Algiers">Al Jazair (Algiers) <OPTION value="Khartoum">Al-Khartkm (Khartoum) <OPTION value="Cairo">Al-Qhirah (Cairo) <OPTION value="Amsterdam">Amsterdam <OPTION value="Anchorage">Anchorage <OPTION value="Ankara">Ankara <OPTION value="Riyadh">Ar-Riyd (Riyadh) <OPTION value="Asuncion">Asunción <OPTION value="Athens">Athínai (Athens) <OPTION value="Atlanta">Atlanta <OPTION value="Auckland">Auckland <OPTION value="Baghdad">Baghdd <OPTION value="Baku">Bak1 (Baku) <OPTION value="Bandung">Bandung <OPTION value="Bangalore">Bangalore <OPTION value="Barcelona">Barcelona <OPTION value="Barranquilla">Barranquilla <OPTION value="Beijing">Beijing <OPTION value="Belem">Belém <OPTION value="Belo Horizonte">Belo Horizonte <OPTION value="Belgrade">Beograd (Belgrade) <OPTION value="Berlin">Berlin <OPTION value="Birmingham">Birmingham (England) <OPTION value="Bogota">Bogotá <OPTION value="Boston">Boston <OPTION value="Brasília">Brasília <OPTION value="Brisbane">Brisbane <OPTION value="Brussels">Bruxelles (Brussels) <OPTION value="Bucharest">Bucure_ti (Bucharest) <OPTION value="Budapest">Budapest <OPTION value="Buenos Aires">Buenos Aires <OPTION value="Busan">Busan <OPTION value="Cali">Cali <OPTION value="Campinas">Campinas <OPTION value="Cape Town">Cape Town <OPTION value="Caracas">Caracas <OPTION value="Cardiff">Cardiff <OPTION value="Casablanca">Casablanca <OPTION value="Changchun">Changchun <OPTION value="Changsha">Changsha <OPTION value="Chengdu">Chengdu <OPTION value="Madras">Chennai (Madras) <OPTION value="Chicago">Chicago <OPTION value="Chittagong">Chittagong <OPTION value="Chongqing">Chongqing <OPTION value="Cincinnati">Cincinnati <OPTION value="Guatemala">Ciudad de Guatemala (Guatemala City) <OPTION value="Mexico City">Ciudad de México (Mexico City) <OPTION value="Cleveland">Cleveland <OPTION value="Colombo">Colombo <OPTION value="Curitiba">Curitiba <OPTION value="Daegu">Daegu <OPTION value="Dakar">Dakar <OPTION value="Dairen">Dalian (Dairen) <OPTION value="Dallas">Dallas <OPTION value="Dar es Salaam">Dar es Salaam <OPTION value="Delhi">Delhi <OPTION value="Denver">Denver <OPTION value="Detroit">Detroit <OPTION value="Dacca">Dhaka (Dacca) <OPTION value="Damascus">Dimashq (Damascus) <OPTION value="Donets'k">Donets'k <OPTION value="Dongguan">Dongguan <OPTION value="Douala">Douala <OPTION value="Dublin">Dublin <OPTION value="Durban">Durban <OPTION value="Faisalabad">Faisalabad <OPTION value="Fortaleza">Fortaleza <OPTION value="Frankfurt">Frankfurt am Main <OPTION value="Fukuoka">Fukuoka <OPTION value="Glasgow">Glasgow <OPTION value="Goiania">Goiânia <OPTION value="Guadalajara">Guadalajara <OPTION value="Guangzhou">Guangzhou (Canton) <OPTION value="Guayaquil">Guayaquil <OPTION value="Guiyang">Guiyang <OPTION value="Hamburg">Hamburg <OPTION value="Hanoi">Hà NÙi (Hanoi) <OPTION value="Hangchow">Hangzhou (Hangchow) <OPTION value="Hanover">Hanover <OPTION value="Harare">Harare (Salisbury) <OPTION value="Harbin">Harbin <OPTION value="Helsinki">Helsinki <OPTION value="Honolulu">Honolulu <OPTION value="Houston">Houston <OPTION value="Hyderabad">Hyderbd <OPTION value="Ibadan">Ibadan <OPTION value="Indore">Indore <OPTION value="Istanbul">Istanbul <OPTION value="Izmir">Izmir <OPTION value="Jaipur">Jaipur <OPTION value="Jakarta">Jakarta <OPTION value="Jiddah">Jiddah <OPTION value="Jilin">Jilin <OPTION value="Jinan">Jinan <OPTION value="Johannesburg">Johannesburg <OPTION value="Kabul">Kbol (Kabul) <OPTION value="Kandahar">Kandahar (Qandahr) <OPTION value="Knpur">Knpur <OPTION value="Kano">Kano <OPTION value="Kansas City">Kansas City <OPTION value="Kaohsiung">Kaohsiung <OPTION value="Karachi">Karchi <OPTION value="Katowice">Katowice <OPTION value="Kinshasa">Kinshasa <OPTION value="Klaipeda">Klaipeda (Memel) <OPTION value="Copenhagen">København (Copenhagen) <OPTION value="Calcutta">Kolkata (Calcutta) <OPTION value="Bangkok">Krung Thep (Bangkok) <OPTION value="Kuala Lumpur">Kuala Lumpur <OPTION value="Kunming">Kunming <OPTION value="Kiev">Kyyiv (Kiev) <OPTION value="Lagos">Lagos <OPTION value="Havana">La Habana (Havana) <OPTION value="Lahore">Lahore <OPTION value="Lanzhou">Lanzhou <OPTION value="Leeds">Leeds <OPTION value="Lima">Lima <OPTION value="Lisbon">Lisboa (Lisbon) <OPTION value="London">London <OPTION value="Los Angeles">Los Angeles <OPTION value="Luanda">Luanda <OPTION value="Lucknow">Lucknow <OPTION value="Madrid">Madrid <OPTION value="Manchester">Manchester <OPTION value="Manila">Manila <OPTION value="Maracaibo">Maracaibo <OPTION value="Medan">Medan <OPTION value="Medellin">Medellin <OPTION value="Melbourne">Melbourne <OPTION value="Miami">Miami <OPTION value="Milan">Milano <OPTION value="Minneapolis">Minneapolis <OPTION value="Monterrey">Monterrey <OPTION value="Montevideo">Montevideo <OPTION value="Montréal">Montréal <OPTION value="Moscow">Moskva (Moscow) <OPTION value="Munich">München (Munich) <OPTION value="Mumbai">Mumbai (Bombay) <OPTION value="Nagpur">Ngpur <OPTION value="Nagoya">Nagoya <OPTION value="Nairobi">Nairobi <OPTION value="Nanking">Nanjing (Nanking) <OPTION value="Napoli">Napoli (Naples) <OPTION value="New York">New York <OPTION value="Osaka">Lsaka <OPTION value="Orlando">Orlando <OPTION value="Ottawa">Ottawa <OPTION value="Pyongyang">P'yOngyang <OPTION value="Paris">Paris <OPTION value="Patna">Patna <OPTION value="Perth">Perth (Australia) <OPTION value="Philadelphia">Philadelphia <OPTION value="Phoenix">Phoenix <OPTION value="Pittsburgh">Pittsburgh <OPTION value="Port-au-Prince">Port-au-Prince <OPTION value="Port Elizabeth">Port Elizabeth <OPTION value="Portland">Portland (Oregon) <OPTION value="Porto Alegre">Porto Alegre <OPTION value="Prague">Praha (Prague) <OPTION value="Pretoria">Pretoria <OPTION value="Puebla">Puebla de Zaragoza <OPTION value="Poona">Pune (Poona) <OPTION value="Qingdao">Qingdao (Tsingtao) <OPTION value="Rawalpindi">Rwalpindi <OPTION value="Recife">Recife <OPTION value="Reykjavik">Reykjavík <OPTION value="Rio de Janeiro">Rio de Janeiro <OPTION value="Roma">Roma (Rome) <OPTION value="Sao Paulo">São Paulo <OPTION value="Sacramento">Sacramento <OPTION value="San Antonio">San Antonio <OPTION value="San Diego">San Diego <OPTION value="San Francisco">San Francisco <OPTION value="San Juan">San Juan <OPTION value="San Salvador">San Salvador <OPTION value="Saint Petersburg">Sankt-Peterburg (Saint Petersburg) <OPTION value="Santiago">Santiago <OPTION value="Santo Domingo">Santo Domingo <OPTION value="Sapporo">Sapporo <OPTION value="Seattle">Seattle <OPTION value="Soul">Soul (Seoul) <OPTION value="Shanghai">Shanghai <OPTION value="Shenyang">Shenyang <OPTION value="Shenzhen">Shenzhen <OPTION value="Shijiazhuang">Shijiazhuang <OPTION value="Singapore">Singapore <OPTION value="Saint Louis">Saint Louis <OPTION value="Stockholm">Stockholm <OPTION value="Stuttgart">Stuttgart <OPTION value="Surat">Skrat <OPTION value="Surabaja">Surabaja <OPTION value="Sydney">Sydney <OPTION value="Taipei">T'ai-pei <OPTION value="Taiyuan">Taiyuan <OPTION value="Tampa">Tampa <OPTION value="Tbilisi">Tbilisi <OPTION value="Tehran">Tehrn <OPTION value="Tel Aviv">Tel Aviv <OPTION value="Ho Chi Minh City">Thanh Pho Ho Chi Minh (Ho Chi Minh City) <OPTION value="Tianjin">Tianjin (Tientsin) <OPTION value="Tokyo">TMkyM <OPTION value="Toronto">Toronto <OPTION value="Toshkent">Toshkent (Tashkent) <OPTION value="Tunis">Tknis <OPTION value="Urumqi">Urumqi <OPTION value="Vancouver">Vancouver <OPTION value="Wagga">Wagga Wagga <OPTION value="Warszawa">Warszawa (Warsaw) <OPTION value="Washington">Washington D.C. <OPTION value="Wien">Wien (Vienna) <OPTION value="Wijchen">Wijchen <OPTION value="Wuhan">Wuhan <OPTION value="Sian">Xi'an (Sian) <OPTION value="Yangon">Yangon (Rangoon) <OPTION value="Yerevan">Yerevan <OPTION value="Zhengzhou">Zhengzhou <OPTION value="Zurich">Zürich </SELECT> </div> <div id='dpick'> <p> <input type="button" value=" Go! " onClick="Cselect(this.form)"> </div> </form> <p ID="ThePic" class="display"> <p ID="Coordinates"> <!-- Calculate GST and LST for current time on user's clock --> <p ID="pGST"> <p align="center"> <font size = "-1"> <a href="http://www.philatelicgems.com/astronomy/findLST.html">CHOOSE ANOTHER CITY</a> <br><a href="http://www.philatelicgems.com/">BACK TO HOME PAGE</a> <p> <B>Contact Me</B><br> <b>E-MAIL:</b> <script language="JavaScript" type="text/JavaScript"><!-- document.write('<a href=\"mailto:' + name + '@' + domain + "?subject=" + item + '\">'); document.write(name + '@' + domain + '<\/a>'); // --></script> <p> <font face="Arial, Helvetica, sans-serif" color="#0032A1" size="-1"> &#169; Sandra Rout 2010</font> </td> </tr> </table> </td> <td width="30" bgcolor="#990000">&nbsp;</td> </tr> <tr bgcolor="#000033"> <td></td><td></td><td></td> </tr> <tr bgcolor="#0032A1"> <td width="131" height="30">&nbsp;</td> <td height="30">&nbsp;</td> <td width="30" height="30">&nbsp;</td> </tr> </table> </div> </BODY> </HTML>