Explanation of the Solar System Ephemeris request form

General Comments

The form allows you to enter the data for the observation's date, time and location.

The default for the location is 90 degrees west longitude, 40 degrees north latitude, 2 miles southwest of Atterbury, IL. This site, along with mean center of US population for 1990 and 2000, is in the US Central Time Zone. The default Date and Time are the current date and time in that time zone, and the UTC Adjustment is either -6 hours for standard time, or -5 hours for daylight saving time. All of the defaults are applied independently; if you make an entry in the hour field, but not the minute or second field, the program will use the default minute and second for those two fields.

The Day must be valid for the given Year and Month. Use 24-hour format for Hour; enter clock times after noon as 12 + clock time. Thus, enter 8 PM as 20.

For the longitude and latitude you can use either the (A) or (B) line; the program which reads the form will note an error if you use both forms. Once you have submitted the form, you can bookmark the result. Then, when you use that bookmark, the longitude and latitude will be correctly set for your location.

You may have to do some research to determine the correct values for a few of the fields: UTC Adjustment (Time - UTC), longitude and latitude.

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UTC Adjustment (Time - UTC)

The UTC Adjustment is the difference between your time and coordinated universal time (UTC). Hour is a signed quantity; West longitude sites (all of the Americas) tend to have negative adjustments; east longitude sites (Europe and Asia) tend to have positive adjustments. There are, of course, exceptions. For example, some islands in the Pacific Ocean which were formerly dependents of New Zealand, at about 155° West longitude, have a UTC Adjustment of +14 hours. Some countries maintain adjustments to UTC that are not whole hours, and so a Minute field (unsigned) is available.

To determine your UTC Adjustment:

1. In the US, WWV (2.5, 5, 10, 15 and 20 MHz shortwave, Fort Collins, CO) and WWVH (2.5, 5, 10, and 15 MHz shortwave, Kauai, HI) broadcast the current UTC. Subtract from your local time to get the current UTC Adjustment.

2. For the United States, the UTC adjustments in hours are:

Zone Name	Standard Time	Daylight Saving Time
Atlantic	-4	-3
Eastern	-5	-4
Central	-6	-5
Mountain	-7	-6
Pacific	-8	-7
Alaska	-9	-8
Aleutian	-10	-9
Hawaii	-10	(none)
Samoa	-11	(none)

3. For more information, try the World Time Zone map.

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Longitude and Latitude

Longitude and Latitude are the coordinates of a location on the Earth. Longitude is the angular distance west or east of the prime meridian (longitude zero, the meridian that passes through Greenwich, England); Latitude is the angular distance north or south of the equator.

The form allows two different entry methods for each of Longitude and Latitude. You can enter each as a number with (A) Degrees, a decimal point and decimals (for example, 91.2152778), or as (B) Degrees, Minutes, Seconds (for example, 91 12 55 in three separate form fields). Use either the (A) or (B) line for Longitude and Latitude but not both; the program will note an error if you use both forms.

If you're just trying to answer some simple visual astronomy questions ("What's the bright object in the East before dawn?" or "Which of those bright objects in the Southwest sky is Jupiter?"), you only need to specify the nearest degree (or even the nearest ten degrees) of longitude and latitude. If you're trying to place the solar system objects on a star atlas, you should be more precise.

To determine your Longitude and Latitude:

1. You could use a printed map for your area. A good atlas will mark each degree of longitude and latitude, and sometimes it will have more precise markings. If you measure distances on the map and interpolate your position, you can easily achieve one-tenth degree accuracy, even on a road atlas. The US Geological Survey 7.5 minute Topographic Series maps, which are probably available at your local library, would allow you to determine your longitude and latitude to the nearest arcsecond.

2. For more information, try the US Geological Survey – Geographical Names Information System web site.

Equinox

You can choose which equinox to use. Prefer Equinox of Date when setting up a telescope for observing, and Equinox J2000.0 when matching sky objects to a star atlas which uses that equinox.

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Sample Form

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Form fields

Field	Max Length	Example	Min	Max	Default
Date:
Year	4	2000	1885	2099	Current year, US Central Time Zone
Month	2	6	1	12	Current month, US Central TZ
Day	2	23	1	31	Current day, US Central TZ
Time:
Hour	2	22	0	23	Current hour, US Central TZ
Minute	2	0	0	59	Current minute, US Central TZ
Second	2	0	0	59	Current second, US Central TZ
UTC Adjustment (Time - UTC):
Hour	3	-5	-14	+14	Current adjustment, US Central TZ
Minute	2	0	0	59	0
Longitude:
West or East			West	East	West
(A) Degrees, decimal point and decimals
	10	97.215	0.0	180.0	90.0
(B) Degrees	3	91	0	180	(none)
(B) Minutes	2	12	0	59	(none)
(B) Seconds	2	55	0	59	(none)
Latitude:
North or South			North	South	North
(A) Degrees, decimal point and decimals
	10	37.872	0.0	90.0	40.0
(B) Degrees	2	37	0	90	(none)
(B) Minutes	2	52	0	59	(none)
(B) Seconds	2	20	0	59	(none)
Equinox:
of Date or J2000.0			of Date	J2000.0	Equinox of Date

Click here to get an ephemeris table using all the defaults, or use your browser's back button to return to the form that you were working with.

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Web site comments, criticisms and complaints: E-mail: Dale Dellutri .
Copyright 2020 Dale A. Dellutri
Last modified: Saturday, 04-Feb-2023 12:47:42 EST