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01/22/2019 – Ephemeris – What the heck is an ephemeris?

January 22, 2019 Comments off

Ephemeris for Tuesday, January 22nd. Today the Sun will be up for 9 hours and 25 minutes, setting at 5:37, and it will rise tomorrow at 8:11. The Moon, 1 day past full, will rise at 7:41 this evening.

What the heck is an ephemeris? According to Wikipedia: “In astronomy and celestial navigation, an ephemeris (plural: ephemerides; from Latin ephemeris, meaning ‘diary’, from the Greek,… meaning ‘diary, <or> journal’) gives the positions of… astronomical objects… at a given time or times. Historically, positions were given as printed tables of values, given at regular intervals of date and time.” My tables are now databases which I generate for the year during the prior December from published algorithms. I will show all on my blog today: It’s at bobmoler.wordpress.com. (You are already here)  I used to have to interpolate values from printed ephemerides.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

An ephemeris

Here are sections of an ephemeris of the positions of 2014 MU69, Ultima Thule that the New Horizons flew past on New Years day. Created by JPL’s Horizons web site.

R.A. is right ascension – East-west position in the sky, like longitude on the Earth, only it’s in hours, minutes and seconds.  One hour = 15 degrees.

DEC is declination – North-south position, in the sky, exactly like latitude on the Earth in degrees, minutes and seconds.

J2000.0 means that the above coordinates are based on where the vernal equinox point in the sky was on January 1, 12:00 Terrestrial Time, 2000.  Or January 1, 2000, 11:58:55.816 UTC as reported in Wikipedia.

APmag – Apparent visual magnitude.  Magnitudes are like golf scores.  The higher magnitude the dimmer the object.  It’s really, really, really dim.

delta – Distance from the Earth in terms of Astronomical Units (AU).  1 AU is Earth’s mean distance from the Sun.

deldot – The change in delta.  Note that is negative.  5 days after New Horizons passed Ultima Thule that spacecraft and Ultima Thule passed behind the Sun.  Now the Earth in its orbit is approaching Ultima as we are coming around the Sun.

How my data is created

LU for DOS

I use my LookingUp for DOS program to generate sunrise/sunset, moonrise/moonset tables for the year.  I also create planetary ephemeris tables here.

Almanac Master

My Ephemeris Helper program massages the raw data from the above program to create this Almanac Master table.

Intro creation

The first 15 or so seconds of the Ephemeris program is created by the Ephemeris Helper program from the Almanac Master, a Holiday Table, A One Time Event Table created from NASA’s SKYCAL Calendar Table, and Reoccurring Events Table.

Planet Master table

The Planet Master table in the Ephemeris Helper program which I use each Wednesday for planet positions.

LookingUp for Windows

First tab of the LookingUp for Windows program which I don’t use much for the radio program but has uses on this blog and for illustrations for the Stellar Sentinel, the newsletter for the Grand Traverse Astronomical Society, that I edit, which is sent to members and distributed free via email to educators.

Source for the algorithms that I use is Astronomical Algorithms by Jean Meeus, Willmann-Bell 1991.